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1. Search for lepton flavour violation in the eμ continuum with the ATLAS detector in pp collisions at the LHC

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, M, Asai, S, Asfandiyarov, R, and Ask, S

Subjects
Nuclear and Plasma Physics, Particle and High Energy Physics, Physical Sciences, ATLAS Collaboration, hep-ex, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics, Astronomical sciences, Atomic, molecular and optical physics, Particle and high energy physics
Abstract

This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ([Formula: see text]) in the e±μ∓ continuum using 2.1 fb-1 of data collected by the ATLAS detector in [Formula: see text]pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass ([Formula: see text]). The upper limits on the production cross section for pp→eμX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for [Formula: see text] to 30 fb for [Formula: see text].

Published
2012

2. Search for lepton flavour violation in the eμ continuum with the ATLAS detector in [Formula: see text]pp collisions at the LHC.

Author

ATLAS Collaboration, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, and Asai, M

Subjects
ATLAS Collaboration, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics
Abstract

This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ([Formula: see text]) in the e±μ∓ continuum using 2.1 fb-1 of data collected by the ATLAS detector in [Formula: see text]pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass ([Formula: see text]). The upper limits on the production cross section for pp→eμX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for [Formula: see text] to 30 fb for [Formula: see text].

Published
2012

3. A measurement of Lorentz Angle of radiation-hard Pixel Sensors

Author

Aleppo, M.

Subjects
Physics - Instrumentation and Detectors
Abstract

Silicon pixel detectors developed to meet LHC requirements were tested in a beam at CERN in the framework of the ATLAS collaboration. The experimental behaviour of irradiated and not-irradiated sensors in a magnetic field is discussed. The measurement of the Lorentz angle for these sensors at different operating conditions is presented. A simple model of the charge drift in silicon before and after irradiation is presented. The good agreement between the model predictions and the experimental results is shown., Comment: 6 pages, 5 figures. Presented at Pixel 2000 conference (Genoa, Italy, june 2000). To be published in the Prooceedings of the conference on NIM

Published
2000
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4. Measurement of the differential cross-sections of inclusive, prompt and non-prompt J/ψ production in proton–proton collisions at s=7 TeV

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, and Asai, S

Subjects
hep-ex, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics
Abstract

The inclusive J/Ψ production cross-section and fraction of J/Ψ mesons produced in B-hadron decays are measured in proton-proton collisions at √s=7 TeV with the ATLAS detector at the LHC, as a function of the transverse momentum and rapidity of the J/Ψ, using 2.3 pb-1 of integrated luminosity. The cross-section is measured from a minimum pT of 1 GeV to a maximum of 70 GeV and for rapidities within |y|

Published
2011

5. Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in s=7 TeV proton–proton collisions

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, and Ask, S

Subjects
Supersymmetry, Squark, Gluino, Search, LHC, ATLAS, hep-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

A search for squarks and gluinos in final states containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded by the ATLAS experiment in √s=7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 35 pb-1 of analysed data. Gluino masses below 500 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion increases to 870 GeV for equal mass squarks and gluinos. In MSUGRA/CMSSM models with tanβ=3, A0=0 and μ>0, squarks and gluinos of equal mass are excluded below 775 GeV. These are the most stringent limits to date. © 2011 CERN.

Published
2011

6. Search for high-mass states with one lepton plus missing transverse momentum in proton–proton collisions at s=7 TeV with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Ali, S, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Bella, LA, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, and Asai, S

Subjects
Exotics, Electroweak interaction, Particle and resonance production, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W′,W⁎), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb−1. No excess beyond standard model expectations is observed. A W′ with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W⁎ (charged chiral boson) for masses below 1.35 TeV.

Published
2011

7. Search for stable hadronising squarks and gluinos with the ATLAS experiment at the LHC

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TP, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, LA, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, Ask, S, and Åsman, B

Subjects
Supersymmetry, Long-lived particle, R-hadron, Limit, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this Letter a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton–proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb−1. No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of squarks and gluinos. The influence of R-hadron interactions in matter was studied using a number of different models, and lower mass limits for stable sbottoms and stops are found to be 294 and 309 GeV respectively. The lower mass limit for a stable gluino lies in the range from 562 to 586 GeV depending on the model assumed. Each of these constraints is the most stringent to date.

Published
2011

8. Measurement of underlying event characteristics using charged particles in pp collisions at s=900 GeV and 7 TeV with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, and Artamonov, A

Subjects
hep-ex, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics
Abstract

Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The "underlying event" is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged particle multiplicity, transverse momentum density, and average pT are measured. The data show generally higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data. © 2011 American Physical Society.

Published
2011

9. Search for high-mass states with one lepton plus missing transverse momentum in proton–proton collisions at s=7 TeV with the ATLAS detector

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Ali, S, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
Exotics, Electroweak interaction, Particle and resonance production, hep-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W′,W⁎), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb−1. No excess beyond standard model expectations is observed. A W′ with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W⁎ (charged chiral boson) for masses below 1.35 TeV.

Published
2011

10. Search for stable hadronising squarks and gluinos with the ATLAS experiment at the LHC

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TP, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, and Ask, S

Subjects
Supersymmetry, Long-lived particle, R-hadron, Limit, hep-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this Letter a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton–proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb−1. No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of squarks and gluinos. The influence of R-hadron interactions in matter was studied using a number of different models, and lower mass limits for stable sbottoms and stops are found to be 294 and 309 GeV respectively. The lower mass limit for a stable gluino lies in the range from 562 to 586 GeV depending on the model assumed. Each of these constraints is the most stringent to date.

Published
2011

11. Measurement of underlying event characteristics using charged particles in pp collisions at √s=900GeV and 7 TeV with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Ákesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, and Artamonov, A

Subjects
hep-ex, Nuclear & Particles Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The "underlying event" is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged particle multiplicity, transverse momentum density, and average pT are measured. The data show generally higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data. © 2011 American Physical Society.

Published
2011

12. Measurements of underlying-event properties using neutral and charged particles in pp collisions at GeV and TeV with the ATLAS detector at the LHC

Author

The ATLAS Collaboration, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, and Ask, S

Subjects
Nuclear and Plasma Physics, Particle and High Energy Physics, Synchrotrons and Accelerators, Physical Sciences, hep-ex, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics, Astronomical sciences, Atomic, molecular and optical physics, Particle and high energy physics
Abstract

We present first measurements of charged and neutral particle-flow correlations in pp collisions using the ATLAS calorimeters.Data were collected in 2009 and 2010 at centre-of-mass energies of 900 GeV and 7 TeV.Events were selected using a minimum-bias trigger which required a charged particle in scintillation counters on either side of the interaction point.Particle flows, sensitive to the underlying event, are measured using clusters of energy in the ATLAS calorimeters, taking advantage of their fine granularity.No Monte Carlo generator used in this analysis can accurately describe the measurements.The results are independent of those based on charged particles measured by the ATLAS tracking systems and can be used to constrain the parameters of Monte Carlo generators.

Published
2011

13. A search for new physics in dijet mass and angular distributions in pp collisions at TeV measured with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, and Asfandiyarov, R

Subjects
hep-ex, Physical Sciences, Fluids & Plasmas
Abstract

A search for new interactions and resonances produced in LHC proton-proton (pp) collisions at a centre-of-mass energy √s = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb -1, dijet mass and angular distributions were measured up to dijet masses of ∼3.5TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space-time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale A below 9.5 TeV. © 2011 CERN for the benefit of the ATLAS Collaboration.

Published
2011

14. Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
hep-ex, Physical Sciences, Fluids & Plasmas
Abstract

Measurements are presented from proton-proton collisions at centre-of-mass energies of s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimumbias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with pT < 100 MeV, is measured to be 3.483±0.009 (stat)±0.106 (syst) at s = 0.9 TeV and 5.630±0.003 (stat)±0.169 (syst) at s = 7 TeV. © 2011 CERN for the benefit of the ATLAS Collaboration, published under licence by IOP Publishing Ltd for the Institute of Physics and Deutsche Physikalische Gesellschaft.

Published
2011

15. Measurement of dijet azimuthal decorrelations in pp collisions at sqrt(s)=7  TeV.

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, and Ask, S

Subjects
ATLAS Collaboration, hep-ex, General Physics, Mathematical Sciences, Physical Sciences, Engineering
Abstract

Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full data set (∫Ldt=36  pb(-1)) acquired by the ATLAS detector during the 2010 sqrt(s)=7  TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high-energy regime.

Published
2011

16. Search for massive long-lived highly ionising particles with the ATLAS detector at the LHC

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, and Ask, S

Subjects
High-energy collider experiment, Long-lived particle, Highly ionising, New physics, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

A search is made for massive highly ionising particles with lifetimes in excess of 100 ns, with the ATLAS experiment at the Large Hadron Collider, using 3.1 pb-1 of pp collision data taken at √s=7 TeV. The signature of energy loss in the ATLAS inner detector and electromagnetic calorimeter is used. No such particles are found and limits on the production cross section for electric charges 6e≤|q|≤17e and masses 200 GeV≤m≤1000 GeV are set in the range 1-12 pb for different hypotheses on the production mechanism. © 2011 CERN.

Published
2011

17. Measurement of the production cross section for W-bosons in association with jets in pp collisions at √s=7 TeV with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
W-boson, Jets, ATLAS, LHC, Proton-proton, TeV, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

This Letter reports on a first measurement of the inclusive W+jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W-boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections σ(W+≥n)/σ(W+≥n-1) for inclusive jet multiplicities n=1-4. The results, based on an integrated luminosity of 1.3 pb-1, have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n≤2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities. © 2011 CERN Elsevier B.V.

Published
2011

18. Luminosity determination in pp collisions at TeV using the ATLAS detector at the LHC

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, and Artoni, G

Subjects
Nuclear and Plasma Physics, Particle and High Energy Physics, Physical Sciences, Bioengineering, hep-ex, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics, Astronomical sciences, Atomic, molecular and optical physics, Particle and high energy physics
Abstract

Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at √s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0 < μ < 2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most ±2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation. © CERN for the benefit of the ATLAS collaboration 2011.

Published
2011

19. Measurement of the production cross section for W-bosons in association with jets in pp collisions at s=7 TeV with the ATLAS detector

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, and Artoni, G

Subjects
W-boson, Jets, ATLAS, LHC, Proton-proton, TeV, hep-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

This Letter reports on a first measurement of the inclusive W+jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W-boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections σ(W+≥n)/σ(W+≥n-1) for inclusive jet multiplicities n=1-4. The results, based on an integrated luminosity of 1.3 pb-1, have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n≤2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities. © 2011 CERN Elsevier B.V.

Published
2011

20. Search for massive long-lived highly ionising particles with the ATLAS detector at the LHC

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, and Asfandiyarov, R

Subjects
High-energy collider experiment, Long-lived particle, Highly ionising, New physics, hep-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

A search is made for massive highly ionising particles with lifetimes in excess of 100 ns, with the ATLAS experiment at the Large Hadron Collider, using 3.1 pb-1 of pp collision data taken at √s=7 TeV. The signature of energy loss in the ATLAS inner detector and electromagnetic calorimeter is used. No such particles are found and limits on the production cross section for electric charges 6e≤|q|≤17e and masses 200 GeV≤m≤1000 GeV are set in the range 1-12 pb for different hypotheses on the production mechanism. © 2011 CERN.

Published
2011

21. Luminosity determination in pp collisions at √s = 7 TeV using the ATLAS detector at the LHC

Author

Aad, D, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Akesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, N, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amoros, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, and Artoni, G

Subjects
hep-ex, Nuclear & Particles Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at √s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0 < μ < 2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most ±2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation. © CERN for the benefit of the ATLAS collaboration 2011.

Published
2011

22. Search for supersymmetry using final states with one lepton, jets, and missing transverse momentum with the ATLAS detector in √s=7 TeV pp collisions.

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, and Ask, S

Subjects
ATLAS Collaboration, hep-ex, General Physics, Mathematical Sciences, Physical Sciences, Engineering
Abstract

This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from √s=7  TeV proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35  pb(-1). No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. Within this framework, for A(0)=0 GeV, tanβ=3, and μ>0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.

Published
2011

23. Search for diphoton events with large missing transverse energy in 7 TeV proton-proton collisions with the ATLAS detector.

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
ATLAS Collaboration, hep-ex, General Physics, Mathematical Sciences, Physical Sciences, Engineering
Abstract

A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at √s=7 TeV at the CERN Large Hadron Collider and correspond to an integrated luminosity of 3.1 pb⁻¹. No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R

Published
2011

24. Measurement of the inclusive isolated prompt photon cross section in pp collisions at √s=7TeV with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andari, N, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, and Artoni, G

Subjects
hep-ex, Nuclear & Particles Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy √s=7TeV is presented. The measurement covers the pseudorapidity ranges |ηγ|

Published
2011

25. Measurement of the centrality dependence of J/Ψ yields and observation of Z production in lead-lead collisions with the ATLAS detector at the LHC

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
ATLAS, LHC, Heavy ions, J/psi, Z boson, Centrality dependence, hep-ex, nucl-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Using the ATLAS detector, a centrality-dependent suppression has been observed in the yield of J/Ψ mesons produced in the collisions of lead ions at the Large Hadron Collider. In a sample of minimum-bias lead-lead collisions at a nucleon-nucleon centre of mass energy sNN=2.76 TeV, corresponding to an integrated luminosity of about 6.7 μb-1, J/Ψ mesons are reconstructed via their decays to μ+μ- pairs. The measured J/Ψ yield, normalized to the number of binary nucleon-nucleon collisions, is found to significantly decrease from peripheral to central collisions. The centrality dependence is found to be qualitatively similar to the trends observed at previous, lower energy experiments. The same sample is used to reconstruct Z bosons in the μ+μ- final state, and a total of 38 candidates are selected in the mass window of 66 to 116 GeV. The relative Z yields as a function of centrality are also presented, although no conclusion can be inferred about their scaling with the number of binary collisions, because of limited statistics. This analysis provides the first results on J/Ψ and Z production in lead-lead collisions at the LHC. © 2011 CERN.

Published
2011

26. Study of jet shapes in inclusive jet production in pp collisions at √s=7TeV using the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
hep-ex, Nuclear & Particles Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Jet shapes have been measured in inclusive jet production in proton-proton collisions at √s=7TeV using 3pb-1 of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30GeV

Published
2011

27. Measurement of the top quark-pair production cross section with ATLAS in pp collisions at TeV

Author

The ATLAS Collaboration, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, and Arnault, C

Subjects
Nuclear and Plasma Physics, Particle and High Energy Physics, Physical Sciences, hep-ex, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics, Astronomical sciences, Atomic, molecular and optical physics, Particle and high energy physics
Abstract

A measurement of the production cross-section for top quark pairs (tt̅) in pp collisions at √s =7 TeVis presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron e or muon μ) with large missing transverse energy and at least four jets, and dilepton (ee, μμ or eμ) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb–1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-tt̅ Standard Model processes are estimated using data-driven methods and determined to be 12.2 ± 3.9 events and 2.5± 0.6 events, respectively. The kinematic properties of the selected events are consistent with SM tt̅ production. The inclusive top quark pair production cross-section is measured to be The measurement agrees with perturbative QCD calculations.

Published
2011

28. Measurement of the inclusive isolated prompt photon cross section in pp collisions at s=7 TeV with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andari, N, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, and Artoni, G

Subjects
hep-ex, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics
Abstract

A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy √s=7TeV is presented. The measurement covers the pseudorapidity ranges |ηγ|

Published
2011

29. Measurement of the centrality dependence of J/ψ yields and observation of Z production in lead–lead collisions with the ATLAS detector at the LHC

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, and Artoni, G

Subjects
ATLAS, LHC, Heavy ions, J/psi, Z boson, Centrality dependence, hep-ex, nucl-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

Using the ATLAS detector, a centrality-dependent suppression has been observed in the yield of J/Ψ mesons produced in the collisions of lead ions at the Large Hadron Collider. In a sample of minimum-bias lead-lead collisions at a nucleon-nucleon centre of mass energy sNN=2.76 TeV, corresponding to an integrated luminosity of about 6.7 μb-1, J/Ψ mesons are reconstructed via their decays to μ+μ- pairs. The measured J/Ψ yield, normalized to the number of binary nucleon-nucleon collisions, is found to significantly decrease from peripheral to central collisions. The centrality dependence is found to be qualitatively similar to the trends observed at previous, lower energy experiments. The same sample is used to reconstruct Z bosons in the μ+μ- final state, and a total of 38 candidates are selected in the mass window of 66 to 116 GeV. The relative Z yields as a function of centrality are also presented, although no conclusion can be inferred about their scaling with the number of binary collisions, because of limited statistics. This analysis provides the first results on J/Ψ and Z production in lead-lead collisions at the LHC. © 2011 CERN.

Published
2011

30. Study of jet shapes in inclusive jet production in pp collisions at s=7 TeV using the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
hep-ex, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics
Abstract

Jet shapes have been measured in inclusive jet production in proton-proton collisions at √s=7TeV using 3pb-1 of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30GeV

Published
2011

31. Measurement of inclusive jet and dijet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector

Author

The ATLAS Collaboration, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, and Armstrong, SR

Subjects
Nuclear and Plasma Physics, Particle and High Energy Physics, Physical Sciences, hep-ex, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics, Astronomical sciences, Atomic, molecular and optical physics, Particle and high energy physics
Abstract

Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb−1 recorded at the Large Hadron Collider. The anti-kt algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable χ. The results are compared to expectations based on next-toleading- order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.

Published
2011

32. Search for quark contact interactions in dijet angular distributions in pp collisions at s=7 TeV measured with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, and Armstrong, SR

Subjects
ATLAS, LHC, TeV, Dijets angular distributions, Quark compositeness, Contact interactions, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Dijet angular distributions from the first LHC pp collisions at center-of-mass energy s=7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet Χ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the λ distributions excludes quark contact interactions with a compositeness scale Χ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits. © 2010 CERN.

Published
2011

33. Search for quark contact interactions in dijet angular distributions in pp collisions at s=7 TeV measured with the ATLAS detector

Author

Collaboration, ATLAS, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, and Arms, KE

Subjects
ATLAS, LHC, TeV, Dijets angular distributions, Quark compositeness, Contact interactions, hep-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

Dijet angular distributions from the first LHC pp collisions at center-of-mass energy s=7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet Χ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the λ distributions excludes quark contact interactions with a compositeness scale Χ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits. © 2010 CERN.

Published
2011

34. Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in √s=7 TeV proton-proton collisions

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, Asfandiyarov, R, Ask, S, and Åsman, B

Subjects
Supersymmetry, Squark, Gluino, Search, LHC, ATLAS, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

A search for squarks and gluinos in final states containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded by the ATLAS experiment in √s=7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 35 pb-1 of analysed data. Gluino masses below 500 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion increases to 870 GeV for equal mass squarks and gluinos. In MSUGRA/CMSSM models with tanβ=3, A0=0 and μ>0, squarks and gluinos of equal mass are excluded below 775 GeV. These are the most stringent limits to date. © 2011 CERN.

Published
2011

35. Measurement of the differential cross-sections of inclusive, prompt and non-prompt J/Ψ production in proton-proton collisions at √s=7 TeV

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, and Asfandiyarov, R

Subjects
hep-ex, Nuclear & Particles Physics, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

The inclusive J/Ψ production cross-section and fraction of J/Ψ mesons produced in B-hadron decays are measured in proton-proton collisions at √s=7 TeV with the ATLAS detector at the LHC, as a function of the transverse momentum and rapidity of the J/Ψ, using 2.3 pb-1 of integrated luminosity. The cross-section is measured from a minimum pT of 1 GeV to a maximum of 70 GeV and for rapidities within |y|

Published
2011

36. Measurement of the top quark-pair production cross section with ATLAS in pp collisions at √s = 7 TeV

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Bella, LA, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, and Artamonov, A

Subjects
hep-ex, Nuclear & Particles Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

A measurement of the production cross-section for top quark pairs (tt̅) in pp collisions at √s =7 TeVis presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron e or muon μ) with large missing transverse energy and at least four jets, and dilepton (ee, μμ or eμ) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb–1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-tt̅ Standard Model processes are estimated using data-driven methods and determined to be 12.2 ± 3.9 events and 2.5± 0.6 events, respectively. The kinematic properties of the selected events are consistent with SM tt̅ production. The inclusive top quark pair production cross-section is measured to be The measurement agrees with perturbative QCD calculations.

Published
2011

37. Measurements of underlying-event properties using neutral and charged particles in pp collisions at √s = 900 GeV and √s = 7 TeV with the ATLAS detector at the LHC

Author

Liang, Z, Martin, B, Meyer, J, Tanaka, S, Thompson, PD, Wang, J, Yang, Y, Yu, J, Zimmermann, S, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, LA, Apolle, R, Arabidze, G, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, and Arik, M

Subjects
hep-ex, Nuclear & Particles Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

We present first measurements of charged and neutral particle-flow correlations in pp collisions using the ATLAS calorimeters.Data were collected in 2009 and 2010 at centre-of-mass energies of 900 GeV and 7 TeV.Events were selected using a minimum-bias trigger which required a charged particle in scintillation counters on either side of the interaction point.Particle flows, sensitive to the underlying event, are measured using clusters of energy in the ATLAS calorimeters, taking advantage of their fine granularity.No Monte Carlo generator used in this analysis can accurately describe the measurements.The results are independent of those based on charged particles measured by the ATLAS tracking systems and can be used to constrain the parameters of Monte Carlo generators.

Published
2011

38. Measurement of inclusive jet and dijet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar- Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood- Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, and Armstrong, SR

Subjects
hep-ex, Nuclear & Particles Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb−1 recorded at the Large Hadron Collider. The anti-kt algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable χ. The results are compared to expectations based on next-toleading- order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.

Published
2011

39. Charged-particle multiplicities in ppinteractions measured with the ATLAS detector at the LHC

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Aperio Bella, L, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
hep-ex, Fluids & Plasmas, Physical Sciences
Abstract

Measurements are presented from proton-proton collisions at centre-of-mass energies of s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimumbias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with pT < 100 MeV, is measured to be 3.483±0.009 (stat)±0.106 (syst) at s = 0.9 TeV and 5.630±0.003 (stat)±0.169 (syst) at s = 7 TeV. © 2011 CERN for the benefit of the ATLAS Collaboration, published under licence by IOP Publishing Ltd for the Institute of Physics and Deutsche Physikalische Gesellschaft.

Published
2011

40. A search for new physics in dijet mass and angular distributions in ppcollisions at √s=7 TeV measured with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Akiyama, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antonov, A, Antos, J, Anulli, F, Aoun, S, Bella, LA, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Arik, E, Arik, M, Armbruster, AJ, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, Arutinov, D, Asai, S, and Asfandiyarov, R

Subjects
hep-ex, Fluids & Plasmas, Physical Sciences
Abstract

A search for new interactions and resonances produced in LHC proton-proton (pp) collisions at a centre-of-mass energy √s = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb -1, dijet mass and angular distributions were measured up to dijet masses of ∼3.5TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space-time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale A below 9.5 TeV. © 2011 CERN for the benefit of the ATLAS Collaboration.

Published
2011

41. Performance of the ATLAS detector using first collision data

Author

Aad, G, Abat, E, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, PF, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosini, G, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Argyropoulos, T, Arik, E, and Arik, M

Subjects
Hadron-Hadron Scattering, hep-ex, Nuclear & Particles Physics, Mathematical Sciences, Physical Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

More than half a million minimum-bias events of LHC collision data were collected by the ATLAS experiment in December 2009 at centre-of-mass energies of 0.9 TeV and 2.36 TeV. This paper reports on studies of the initial performance of the ATLAS detector from these data. Comparisons between data and Monte Carlo predictions are shown for distributions of several track-and calorimeter-based quantities. The good performance of the ATLAS detector in these first data gives confidence for successful running at higher energies.

Published
2010

42. Observation of a centrality-dependent dijet asymmetry in lead-lead collisions at sqrt[S(NN)] =2.76 TeV with the ATLAS detector at the LHC.

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahsan, M, Aielli, G, Akdogan, T, Akesson, TPA, Akimoto, G, Akimov, AV, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Anulli, F, Aoun, S, Bella, L Aperio, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, Arnaez, O, Arnault, C, Artamonov, A, Artoni, G, and Arutinov, D

Subjects
ATLAS Collaboration, hep-ex, nucl-ex, General Physics, Mathematical Sciences, Physical Sciences, Engineering
Abstract

By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

Published
2010

43. Measurement of the W → ℓν and Z/γ* → ℓℓ production cross sections in proton-proton collisions at with the ATLAS detector

Author

The ATLAS Collaboration, Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, and Arms, KE

Subjects
Hadron-Hadron Scattering, hep-ex, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics
Abstract

First measurements of the W → ℓν and Z/γ * → ℓℓ (ℓ = e, μ) production cross sections in proton-proton collisions at √ s = 7TeV are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W → ℓν and 179 Z/γ* → ℓℓ candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb-1. The measured total W and Z/ γ*-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are σtotW · BR(W → ℓν) = 9.96 ± 0.23(stat) ± 0.50(syst) ± 1.10(lumi) nb and σtotZ/γ* · BR(Z/ γ* → ℓℓ) = 0.82 ± 0.06 (stat) ± 0.05 (syst) ± 0.09 (lumi) nb (within the invariant mass window 66 < mℓℓ < 116 GeV). The W/Z cross-section ratio is measured to be 11.7 ± 0.9(stat) ± 0.4(syst). In addition, measurements of the W+ and W- production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.

Published
2010

44. Search for new particles in two-jet final states in 7 TeV proton-proton collisions with the ATLAS detector at the LHC.

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Akesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, Armstrong, SR, and Arnaez, O

Subjects
ATLAS Collaboration, hep-ex, General Physics, Mathematical Sciences, Physical Sciences, Engineering
Abstract

A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the LHC and correspond to an integrated luminosity of 315  nb⁻¹ collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% C.L. the q* mass interval 0.30

Published
2010

45. Performance of the ATLAS detector using first collision data

Author

The ATLAS collaboration, Aad, G, Abat, E, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, PF, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, Å, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosini, G, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Argyropoulos, T, and Arik, E

Subjects
Hadron-Hadron Scattering, hep-ex, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Nuclear & Particles Physics
Abstract

More than half a million minimum-bias events of LHC collision data were collected by the ATLAS experiment in December 2009 at centre-of-mass energies of 0.9 TeV and 2.36 TeV. This paper reports on studies of the initial performance of the ATLAS detector from these data. Comparisons between data and Monte Carlo predictions are shown for distributions of several track-and calorimeter-based quantities. The good performance of the ATLAS detector in these first data gives confidence for successful running at higher energies.

Published
2010

46. Charged-particle multiplicities in pp interactions at √ s = 900 GeV measured with the ATLAS detector at the LHC

Author

Aad, G, Abat, E, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, PF, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albert, J, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosini, G, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Argyropoulos, T, Arik, E, Arik, M, and Armbruster, AJ

Subjects
Charged-particle, Multiplicities, GeV, ATLAS, LHC, Minimum bias, hep-ex, Nuclear & Particles Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and chargedparticle multiplicity are measured for events with at least one charged particle in the kinematic range |η| < 2.5 and pT > 500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at η = 0 is measured to be 1.333 ± 0.003(stat.) ± 0.040(syst.), which is 5-15% higher than the Monte Carlo models predict.

Published
2010

47. Charged-particle multiplicities in pp interactions at s=900 GeV measured with the ATLAS detector at the LHC

Author

Collaboration, ATLAS, Aad, G, Abat, E, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, PF, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albert, J, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosini, G, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, M-L, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, J-F, Argyropoulos, T, Arik, E, and Arik, M

Subjects
Charged-particle, Multiplicities, GeV, ATLAS, LHC, Minimum bias, hep-ex, Mathematical Physics, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics
Abstract

The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and chargedparticle multiplicity are measured for events with at least one charged particle in the kinematic range |η| < 2.5 and pT > 500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at η = 0 is measured to be 1.333 ± 0.003(stat.) ± 0.040(syst.), which is 5-15% higher than the Monte Carlo models predict.

Published
2010

48. Measurement of the W → ℓν and Z/γ* → ℓℓ production cross sections in proton-proton collisions at √ s = 7 TeV with the ATLAS detector

Author

Aad, G, Abbott, B, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, B, Abolins, M, Abramowicz, H, Abreu, H, Acerbi, E, Acharya, BS, Ackers, M, Adams, DL, Addy, TN, Adelman, J, Aderholz, M, Adomeit, S, Adorisio, C, Adragna, P, Adye, T, Aefsky, S, Aguilar-Saavedra, JA, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Ahsan, M, Aielli, G, Akdogan, T, Åkesson, TPA, Akimoto, G, Akimov, AV, Aktas, A, Alam, MS, Alam, MA, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexandre, G, Alexopoulos, T, Alhroob, M, Aliev, M, Alimonti, G, Alison, J, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Almond, J, Aloisio, A, Alon, R, Alonso, A, Alonso, J, Alviggi, MG, Amako, K, Amaral, P, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amorós, G, Amram, N, Anastopoulos, C, Andeen, T, Anders, CF, Anderson, KJ, Andreazza, A, Andrei, V, Andrieux, ML, Anduaga, XS, Angerami, A, Anghinolfi, F, Anjos, N, Annovi, A, Antonaki, A, Antonelli, M, Antonelli, S, Antos, J, Antunovic, B, Anulli, F, Aoun, S, Apolle, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arfaoui, S, Arguin, JF, Argyropoulos, T, Arik, E, Arik, M, Armbruster, AJ, Arms, KE, and Armstrong, SR

Subjects
Hadron-Hadron Scattering, hep-ex, Nuclear & Particles Physics, Mathematical Sciences, Physical Sciences, Mathematical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Quantum Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

First measurements of the W → ℓν and Z/γ * → ℓℓ (ℓ = e, μ) production cross sections in proton-proton collisions at √ s = 7TeV are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W → ℓν and 179 Z/γ* → ℓℓ candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb-1. The measured total W and Z/ γ*-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are σtotW · BR(W → ℓν) = 9.96 ± 0.23(stat) ± 0.50(syst) ± 1.10(lumi) nb and σtotZ/γ* · BR(Z/ γ* → ℓℓ) = 0.82 ± 0.06 (stat) ± 0.05 (syst) ± 0.09 (lumi) nb (within the invariant mass window 66 < mℓℓ < 116 GeV). The W/Z cross-section ratio is measured to be 11.7 ± 0.9(stat) ± 0.4(syst). In addition, measurements of the W+ and W- production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.

Published
2010

49. The ATLAS Experiment at the CERN Large Hadron Collider

Author

Collaboration, The ATLAS, Aad, G, Abat, E, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, BA, Abolins, M, Abramowicz, H, Acerbi, E, Acharya, BS, Achenbach, R, Ackers, M, Adams, DL, Adamyan, F, Addy, TN, Aderholz, M, Adorisio, C, Adragna, P, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Aielli, G, Åkesson, PF, Åkesson, TPA, Akimov, AV, Alam, SM, Albert, J, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexopoulos, T, Alimonti, G, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Aloisio, A, Alonso, J, Alves, R, Alviggi, MG, Amako, K, Amaral, P, Amaral, SP, Ambrosini, G, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amram, N, Anastopoulos, C, Anderson, B, Anderson, KJ, Anderssen, EC, Andreazza, A, Andrei, V, Andricek, L, Andrieux, M-L, Anduaga, XS, Anghinolfi, F, Antonaki, A, Antonelli, M, Antonelli, S, Apsimon, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arguin, J-F, Arik, E, Arik, M, Arms, KE, Armstrong, SR, Arnaud, M, Arnault, C, Artamonov, A, Asai, S, Ask, S, Åsman, B, Asner, D, Asquith, L, Assamagan, K, Astbury, A, Athar, B, Atkinson, T, Aubert, B, Auerbach, B, Auge, E, Augsten, K, Aulchenko, VM, Austin, N, Avolio, G, and Avramidou, R

Subjects
ATLAS, LHC, CERN, Accelerator, Proton-proton collisions, Heavy-ion collisions, Minimum-bias events, Bunch-crossings, Pile-up, Superconducting magnets, Solenoidal field, Toroidal field, Magnetic field measurements, Hall probes, Inner detector, Charged-particle tracking, Vertex measurement, Pixel detectors, Silicon micro-strip detectors, Transition radiation, Time-over-threshold, Radiation-hard electronics, Fluorinert cooling, Carbon-fibre reinforced plastics, Optical fibres, Calorimetry, Sampling calorimeters, Liquid argon, Scintillator tiles, Electromagnetic and hadronic interactions, Forward calorimetry, Accordion geometry, Lateral segmentation, Longitudinal segmentation, Muon spectrometer, Precision-tracking chambers, Trigger chambers, Drift tubes, Thin-gap chambers, Resistive-plate chambers, Optical alignment systems, Forward detectors, Cerenkov light, Roman Pots, Zero-degree calorimetry, Trigger and data acquisition, High-level trigger, Event filter, Detector control system, Bandwidth, Processor farm, Electrons, Muons, Leptons, Photons, Jets, Taus, Missing transverse energy, b-tagging, Particle identification, Tracking algorithms, Vertexing algorithms, Impact parameter measurements, Physical Sciences, Engineering, Nuclear & Particles Physics
Published
2008

50. The ATLAS experiment at the CERN large hadron collider

Author

Aad, G, Abat, E, Abdallah, J, Abdelalim, AA, Abdesselam, A, Abdinov, O, Abi, BA, Abolins, M, Abramowicz, H, Acerbi, E, Acharya, BS, Achenbach, R, Ackers, M, Adams, DL, Adamyan, F, Addy, TN, Aderholz, M, Adorisio, C, Adragna, P, Aharrouche, M, Ahlen, SP, Ahles, F, Ahmad, A, Ahmed, H, Aielli, G, Åkesson, PF, Akesson, TPA, Akimov, AV, Alam, SM, Albert, J, Albrand, S, Aleksa, M, Aleksandrov, IN, Aleppo, M, Alessandria, F, Alexa, C, Alexander, G, Alexopoulos, T, Alimonti, G, Aliyev, M, Allport, PP, Allwood-Spiers, SE, Aloisio, A, Alonso, J, Alves, R, Alviggi, MG, Amako, K, Amaral, P, Amaral, SP, Ambrosini, G, Ambrosio, G, Amelung, C, Ammosov, VV, Amorim, A, Amram, N, Anastopoulos, C, Anderson, B, Anderson, KJ, Anderssen, EC, Andreazza, A, Andrei, V, Andricek, L, Andrieux, ML, Anduaga, XS, Anghinolfi, F, Antonaki, A, Antonelli, M, Antonelli, S, Apsimon, R, Arabidze, G, Aracena, I, Arai, Y, Arce, ATH, Archambault, JP, Arguin, JF, Arik, E, Arik, M, Arms, KE, Armstrong, SR, Arnaud, M, Arnault, C, Artamonov, A, Asai, S, Ask, S, Åsman, B, Asner, D, Asquith, L, Assamagan, K, Astbury, A, Athar, B, Atkinson, T, Aubert, B, Auerbach, B, Auge, E, Augsten, K, Aulchenko, VM, Austin, N, Avolio, G, Avramidou, R, and Axen, A

Subjects
ATLAS, LHC, CERN, Accelerator, Proton-proton collisions, Heavy-ion collisions, Minimum-bias events, Bunch-crossings, Pile-up, Superconducting magnets, Solenoidal field, Toroidal field, Magnetic field measurements, Hall probes, Inner detector, Charged-particle tracking, Vertex measurement, Pixel detectors, Silicon micro-strip detectors, Transition radiation, Time-over-threshold, Radiation-hard electronics, Fluorinert cooling, Carbon-fibre reinforced plastics, Optical fibres, Calorimetry, Sampling calorimeters, Liquid argon, Scintillator tiles, Electromagnetic and hadronic interactions, Forward calorimetry, Accordion geometry, Lateral segmentation, Longitudinal segmentation, Muon spectrometer, Precision-tracking chambers, Trigger chambers, Drift tubes, Thin-gap chambers, Resistive-plate chambers, Optical alignment systems, Forward detectors, Cerenkov light, Roman Pots, Zero-degree calorimetry, Trigger and data acquisition, High-level trigger, Event filter, Detector control system, Bandwidth, Processor farm, Electrons, Muons, Leptons, Photons, Jets, Taus, Missing transverse energy, b-tagging, Particle identification, Tracking algorithms, Vertexing algorithms, Impact parameter measurements, Nuclear & Particles Physics, Other Physical Sciences, Physical Sciences, Engineering
Published
2008

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