Search

CMS Collaboration: et al., Azimuthal correlations of charged particles in xenon-xenon collisions at a center-of-mass energy per nucleon pair of √sNN = 5.44 TeV are studied. The data were collected by the CMS experiment at the LHC with a total integrated luminosity of 3.42μb−1. The collective motion of the system formed in the collision is parametrized by a Fourier expansion of the azimuthal particle density distribution. The azimuthal anisotropy coefficients v2, v3, and v4 are obtained by the scalar-product, two-particle correlation, and multiparticle correlation methods. Within a hydrodynamic picture, these methods have different sensitivities to noncollective and fluctuation effects. The dependence of the Fourier coefficients on the size of the colliding system is explored by comparing the xenon-xenon results with equivalent lead-lead data. Model calculations that include initial-state fluctuation effects are also compared to the experimental results. The observed angular correlations provide new constraints on the hydrodynamic description of heavy ion collisions., SEIDI, CPAN, PCTI, and FEDER (Spain). Individuals have received support from the Marie-Curie program and the European Research Council and Horizon 2020 Grant, Contracts No. 675440 and No. 765710 (European Union); the Programa Estatal de Fomento de la Investigación Científica y Técnica de Excelencia María de Maeztu, Grant No. MDM-2015-0509 and the Programa Severo Ochoa del Principado de Asturias.

The production cross sections of Bs0 mesons and charge conjugates are measured in proton-proton (pp) and PbPb collisions via the exclusive decay channel Bs0→J/ψϕ→μ+μ−K+K− at a center-of-mass energy of 5.02 TeV per nucleon pair and within the rapidity range |y

Exclusive ρ(770)0 photoproduction is measured for the first time in ultraperipheral pPb collisions at √sNN=5.02TeV with the CMS detector. The cross section σ(γp→ρ(770)0p) is 11.0±1.4(stat)±1.0(syst) μb at ⟨Wγp⟩=92.6GeV for photon–proton centre-of-mass energies WγpWγp between 29 and 213GeV. The differential cross section dσ/d|t| is measured in the interval 0.025

The results of a search for a standard model-like Higgs boson in the mass range between 70 and 110 GeV decaying into two photons are presented. The analysis uses the data set collected with the CMS experiment in proton-proton collisions during the 2012 and 2016 LHC running periods. The data sample corresponds to an integrated luminosity of 19.7 (35.9)fb−1 at √s = 8 (13) TeV. The expected and observed 95% confidence level upper limits on the product of the cross section and branching fraction into two photons are presented. The observed upper limit for the 2012 (2016) data set ranges from 129 (161) fb to 31 (26) fb. The statistical combination of the results from the analyses of the two data sets in the common mass range between 80 and 110 GeV yields an upper limit on the product of the cross section and branching fraction, normalized to that for a standard model-like Higgs boson, ranging from 0.7 to 0.2, with two notable exceptions: one in the region around the Z boson peak, where the limit rises to 1.1, which may be due to the presence of Drell–Yan dielectron production where electrons could be misidentified as isolated photons, and a second due to an observed excess with respect to the standard model prediction, which is maximal for a mass hypothesis of 95.3 GeV with a local (global) significance of 2.8 (1.3) standard deviations.

This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at √s = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb−1 at √s = 7 TeV and 12.2 to 20.3 fb−1 at √s = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at √s = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at √s = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 ± 1.4 pb at √s = 8 TeV. The square of the magnitude of the CKM matrix element Vtb multiplied by a form factor fLV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |Vtd|, |Vts| ≪ |Vtb|. All the |fLVVtb|2 determinations, extracted from individual ratios at √s = 7 and 8 TeV, are combined, resulting in |fLVVtb| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.

The modification of jet shapes in Pb-Pb collisions, relative to those in pp collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta (pT) above 1 GeV/c in annuli around the axes of jets with pjetT>30 GeV/c associated with an isolated photon with pγT>60 GeV/c. The jet shape distributions are consistent between peripheral Pb-Pb and pp collisions, but are modified for more central Pb-Pb collisions. In these central Pb-Pb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to pp, reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons.

Measurements of prompt ψ(2S) meson production cross sections in proton–lead (pPb) and proton–proton (pp) collisions at a nucleon–nucleon center-of-mass energy of √sNN=5.02TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb−1 and 28.0 pb−1 , respectively. The nuclear modification factor RpPb is measured for prompt ψ(2S) in the transverse momentum range 4

This Letter describes a search for Higgs boson pair production using the combined results from four final states: bbγγ, bbττ, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at √s =13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the nonresonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250–3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section.

Measurements of differential top quark pair tt¯ cross sections using events produced in proton-proton collisions at a centre-of-mass energy of 13 TeV containing two oppositely charged leptons are presented. The data were recorded by the CMS experiment at the CERN LHC in 2016 and correspond to an integrated luminosity of 35.9 fb−1. The differential cross sections are presented as functions of kinematic observables of the top quarks and their decay products, the tt¯ system, and the total number of jets in the event. The differential cross sections are defined both with particle-level objects in a fiducial phase space close to that of the detector acceptance and with parton-level top quarks in the full phase space. All results are compared with standard model predictions from Monte Carlo simulations with next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD) at matrix-element level interfaced to parton-shower simulations. Where possible, parton-level results are compared to calculations with beyond-NLO precision in QCD. Significant disagreement is observed between data and all predictions for several observables. The measurements are used to constrain the top quark chromomagnetic dipole moment in an effective field theory framework at NLO in QCD and to extract tt¯ and leptonic charge asymmetries.

The CMS Collaboration: et al., A study is presented of anomalous HVV interactions of the Higgs boson, including its CP properties. The study uses Higgs boson candidates produced mainly in vector boson fusion and gluon fusion that subsequently decay to a pair of τ leptons. The data were recorded by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 35.9 fb-1. A matrix element technique is employed for the analysis of anomalous interactions. The results are combined with those from the H→4â.,> decay channel presented earlier, yielding the most stringent constraints on anomalous Higgs boson couplings to electroweak vector bosons expressed as effective cross section fractions and phases: The CP-violating parameter fa3cos(φa3)=(0.00±0.27)×10-3 and the CP-conserving parameters fa2cos(φa2)=(0.08-0.21+1.04)×10-3, fΛ1cos(φΛ1)=(0.00-0.09+0.53)×10-3, and fΛ1Zγcos(φΛ1Zγ)=(0.0-1.3+1.1)×10-3. The current dataset does not allow for precise constraints on CP properties in the gluon fusion process. The results are consistent with standard model expectations., Individuals have received support from the MarieCurie program and the European Research Council and Horizon 2020 Grant, Contract Nos. 675440 and 765710 (European Union); the Programa Estatal de Fomento de la Investigación Científica y T´ecnica de Excelencia María de Maeztu, Grant No. MDM-2015-0509, and the Programa Severo Ochoa del Principado de Asturias.

Measurements are presented of the triple-differential cross section for inclusive isolated-photon+jet events in pppp collisions at √s=8 TeV as a function of photon transverse momentum (pγT), photon pseudorapidity (ηγ), and jet pseudorapidity (ηjet). The data correspond to an integrated luminosity of 19.7fb−1 that probe a broad range of the available phase space, for |ηγ| 25GeV. The measurements are compared to next-to-leading order perturbative quantum chromodynamics calculations, which reproduce the data within uncertainties.

Studies of on-shell and off-shell Higgs boson production in the four-lepton final state are presented, using data from the CMS experiment at the LHC that correspond to an integrated luminosity of 80.2 fb−1 at a center-of-mass energy of 13 TeV. Joint constraints are set on the Higgs boson total width and parameters that express its anomalous couplings to two electroweak vector bosons. These results are combined with those obtained from the data collected at center-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 5.1 and 19.7 fb−1, respectively. Kinematic information from the decay particles and the associated jets are combined using matrix element techniques to identify the production mechanism and to increase sensitivity to the Higgs boson couplings in both production and decay. The constraints on anomalous HVV couplings are found to be consistent with the standard model expectation in both the on-shell and off-shell regions. Under the assumption of a coupling structure similar to that in the standard model, the Higgs boson width is constrained to be 3.2+2.8−2.2 MeV while the expected constraint based on simulation is 4.1+5.0−4.0 MeV. The constraints on the width remain similar with the inclusion of the tested anomalous HVV interactions.

CCombined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton–proton collision data set recorded with the CMS detector in 2016 at √s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a W or Z boson, or a top quarkantiquark pair) and the following decay modes: H → γ γ , ZZ, WW, ꚍ ꚍ , bb, and μμ. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be μ = 1.17 ± 0.10, assuming a Higgs boson mass of 125.09 GeV. Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.

Measurements are presented of associated production of a W boson and a charm quark (W+c) in proton–proton collisions at a center-of-mass energy of 13TeV. The data correspond to an integrated luminosity of 35.7fb−1 collected by the CMS experiment at the CERN LHC. The W bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of D∗(2010)± mesons that decay via D∗(2010)±→D0+π±→K∓+π±+π±D∗. A cross section is measured in the fiducial region defined by the muon transverse momentum pμT>26GeV, muon pseudorapidity |ημ|5GeV. The inclusive cross section for this kinematic range is σ(W+c)=1026±31(stat)+76−72(syst) pb. The cross section is also measured differentially as a function of the pseudorapidity of the muon from the WW boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.

The exclusive photoproduction of Υ(nS) meson states from protons, γp→Υ(nS)p (with n=1,2,3), is studied in ultraperipheral pp Pb collisions at a centre-of-mass energy per nucleon pair of √sNN=5.02TeV . The measurement is performed using the Υ(nS)→μ+μ− decay mode, with data collected by the CMS experiment corresponding to an integrated luminosity of 32.6nb−1. Differential cross sections as functions of the Υ(nS) transverse momentum squared p2T, and rapidity y, are presented. The Υ(1S) photoproduction cross section is extracted in the rapidity range |y

This Letter reports measurements of differential cross sections for the production of two Z bosons in association with jets in proton–proton collisions at √s=8 and 13 TeV. The analysis is based on data samples collected at the LHC with the CMS detector, corresponding to integrated luminosities of 19.7 and 35.9fb−1 at 8 and 13 TeV, respectively. The measurements are performed in the leptonic decay modes ZZ→ℓ+ℓ−ℓ′+ℓ′−, where ℓ,ℓ′=e,μ. The differential cross sections as a function of the jet multiplicity, the transverse momentum pT, and pseudorapidity of the pT -leading and subleading jets are presented. In addition, the differential cross sections as a function of variables sensitive to the vector boson scattering, such as the invariant mass of the two pT -leading jets and their pseudorapidity separation, are reported. The results are compared to theoretical predictions and found in good agreement within the theoretical and experimental uncertainties.

Charge-dependent anisotropy Fourier coefficients (vn) of particle azimuthal distributions are measured in pPb and PbPb collisions at √sNN=5.02TeV with the CMS detector at the LHC. The normalized difference in the second-order anisotropy coefficients (v2) between positively and negatively charged particles is found to depend linearly on the observed event charge asymmetry with comparable slopes for both pPb and PbPb collisions over a wide range of charged particle multiplicity. In PbPb, the third-order anisotropy coefficient v3 shows a similar linear dependence with the same slope as seen for v2. The observed similarities between the v2 slopes for pPb and PbPb, as well as the similar slopes for v2 and v3 in PbPb, are compatible with expectations based on local charge conservation in the decay of clusters or resonances, and constitute a challenge to the hypothesis that, at LHC energies, the observed charge asymmetry dependence of v2 in heavy ion collisions arises from a chiral magnetic wave.

Measurements of the pseudorapidity distributions of charged hadrons produced in xenon-xenon collisions at a nucleon-nucleon centre-of-mass energy of √sNN=5.44 TeV are presented. The measurements are based on data collected by the CMS experiment at the LHC. The yield of primary charged hadrons produced in xenon-xenon collisions in the pseudorapidity range |η

A search for a narrow Z′ gauge boson with a mass between 5 and 70 GeV resulting from an Lμ−Lτ U(1) local gauge symmetry is reported. Theories that predict such a particle have been proposed as an explanation of various experimental discrepancies, including the lack of a dark matter signal in direct-detection experiments, tension in the measurement of the anomalous magnetic moment of the muon, and reports of possible lepton flavor universality violation in B meson decays. A data sample of proton-proton collisions at a center-of-mass energy of 13 TeV is used, corresponding to an integrated luminosity of 77.3 fb−1 recorded in 2016 and 2017 by the CMS detector at the LHC. Events containing four muons with an invariant mass near the standard model Z boson mass are analyzed, and the selection is further optimized to be sensitive to the events that may contain Z→Z′μμ→4μ decays. The event yields are consistent with the standard model predictions. Upper limits of 10−8–10−7 at 95% confidence level are set on the product of branching fractions B(Z→Z′μμ)B(Z′→μμ), depending on the Z′ mass, which excludes a Z′ boson coupling strength to muons above 0.004–0.3. These are the first dedicated limits on Lμ−Lτ models at the LHC and result in a significant increase in the excluded model parameter space. The results of this search may also be used to constrain the coupling strength of any light Z′ gauge boson to muons.

A measurement of the elliptic flow (v2) of prompt J/ψ mesons in high-multiplicity pPb collisions is reported using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy √sNN=8.16TeV. Prompt J/ψ mesons decaying into two muons are reconstructed in the rapidity region in the nucleon-nucleon center-of-mass frame (ycm), corresponding to either −2.86

CMS Collaboration: et al., A search is presented for a heavy pseudoscalar boson A decaying to a Z boson and a Higgs boson with mass of 125GeV. In the final state considered, the Higgs boson decays to a bottom quark and antiquark, and the Z boson decays either into a pair of electrons, muons, or neutrinos. The analysis is performed using a data sample corresponding to an integrated luminosity of 35.9fb−1 collected in 2016 by the CMS experiment at the LHC from proton–proton collisions at a center-of-mass energy of 13TeV. The data are found to be consistent with the background expectations. Exclusion limits are set in the context of two-Higgs-doublet models in the A boson mass range between 225 and 1000GeV., Individuals have received support from the Marie-Curie program and the European Research Council and Horizon 2020 Grant, contract No. 675440 (European Union); the Programa Estatal de Fomento de la Investigación Científica y Técnica de Excelencia María de Maeztu, Grant MDM-2015-0509 and the Programa Severo Ochoa del Principado de Asturias.

Event-by-event fluctuations in the elliptic-flow coefficient v2 are studied in PbPb collisions at √sNN=5.02 TeV using the CMS detector at the CERN LHC. Elliptic-flow probability distributions p(v2) for charged particles with transverse momentum 0.3

A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, Δφ12, is presented. The measurement considers events where the two leading jets are nearly collinear (“back-to-back”) in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb−1 are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with the measurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177º < Δφ12 < 180º. The 2- and 3-jet measurements are not simultaneously described by any of models.

The mass of the top quark is measured using a sample of t t ¯ events collected by the CMS detector using proton-proton collisions at s=13TeV at the CERN LHC. Events are selected with one isolated muon or electron and at least four jets from data corresponding to an integrated luminosity of 35.9fb-1. For each event the mass is reconstructed from a kinematic fit of the decay products to a t t ¯ hypothesis. Using the ideogram method, the top quark mass is determined simultaneously with an overall jet energy scale factor (JSF), constrained by the mass of the W boson in q q ¯ ? decays. The measurement is calibrated on samples simulated at next-to-leading order matched to a leading-order parton shower. The top quark mass is found to be 172.25±0.08(stat+JSF)±0.62(syst)GeV. The dependence of this result on the kinematic properties of the event is studied and compared to predictions of different models of t t ¯ production, and no indications of a bias in the measurements are observed.

A search for a light charged Higgs boson, originating from the decay of a top quark and subsequently decaying into a charm quark and a strange antiquark, is presented. The data used in the analysis correspond to an integrated luminosity of 19.7 fb−1 recorded in proton-proton collisions at s√=8s=8 TeV by the CMS experiment at the LHC. The search is performed in the process tt¯→W±bH∓b¯¯¯tt¯→W±bH∓b¯, where the W boson decays to a lepton (electron or muon) and a neutrino. The decays lead to a final state comprising an isolated lepton, at least four jets and large missing transverse energy. No significant deviation is observed in the data with respect to the standard model predictions, and model-independent upper limits are set on the branching fraction B(t→H+b)B(t→H+b), ranging from 1.2 to 6.5% for a charged Higgs boson with mass between 90 and 160 GeV, under the assumption that B(H+→cs)=100%B(H+→cs)=100%. […] the Secretaría de Estado de Investigación, Desarrollo e Innovación and Programa Consolider-Ingenio 2010, Spain […]

A search for a charged Higgs boson is performed with a data sample corresponding to an integrated luminosity of 19.7 ± 0.5 fb−1 collected with the CMS detector in proton-proton collisions at s√=8s=8,TeV. The charged Higgs boson is searched for in top quark decays for mH± < m t − m b, and in the direct production pp → t(b)H± for m H± > m t − m b. The H± → τ ± ν τand H± → tb decay modes in the final states τ h+jets, μτ h, ℓ+jets, and ℓℓ’ (ℓ =e, μ) are considered in the search. No signal is observed and 95% confidence level upper limits are set on the charged Higgs boson production. A model-independent upper limit on the product branching fraction B(t→H±b)B(H±→τ±ντ)=1.2−0.15%B(t→H±b)B(H±→τ±ντ)=1.2−0.15% is obtained in the mass range m H± = 80–160 GeV, while the upper limit on the cross section times branching fraction σ(pp→t(b)H±)B(H±→ τ±ντ)=0.38−0.025σ(pp→t(b)H±)B(H±→ τ±ντ)=0.38−0.025 pb is set in the mass range m H+ = 180–600 GeV. Here, σ(pp → t(b)H±) stands for the cross section sum σ(pp→t¯(b)H+)+σ(pp→t(b¯¯¯)H−)σ(pp→t¯(b)H+)+σ(pp→t(b¯)H−). Assuming B(H±→tb)=1B(H±→tb)=1, an upper limit on σ(pp → t(b)H±) of 2.0–0.13 pb is set for m H± = 180–600 GeV. The combination of all considered decay modes and final states is used to set exclusion limits in the m H±−tan βparameter space in different MSSM benchmark scenarios. [...] the Secretaría de Estado de Investigación, Desarrollo e Innovación and Programa Consolider-Ingenio 2010, Spain [...]

The pseudorapidity distribution of charged hadrons in pp collisions at vs=13TeV is measured using a data sample obtained with the CMS detector, operated at zero magnetic field, at the CERN LHC. The yield of primary charged long-lived hadrons produced in inelastic pp collisions is determined in the central region of the CMS pixel detector (|?

The first search for supersymmetry in the vector-boson fusion topology is presented. The search targets final states with at least two leptons, large missing transverse momentum, and two jets with a large separation in rapidity. The data sample corresponds to an integrated luminosity of 19.7 fb−1 of proton-proton collisions at √s=8 TeV collected with the CMS detector at the CERN LHC. The observed dijet invariant mass spectrum is found to be consistent with the expected standard model prediction. Upper limits are set on the cross sections for chargino and neutralino production with two associated jets, assuming the supersymmetric partner of the τ lepton to be the lightest slepton and the lightest slepton to be lighter than the charginos. For a so-called compressed-mass-spectrum scenario in which the mass difference between the lightest supersymmetric particle χ~01χ~10 and the next lightest, mass-degenerate, gaugino particles χ~02χ~20 and χ~±1χ~1± is 50 GeV, a mass lower limit of 170 GeV is set for these latter two particles.

Esta memoria describe el trabajo fin de máster de la titulación Máster en Física y Tecnologías Físicas de la Universidad de Cantabria. La actividad que aquí se discute ha sido desarrollada entre los meses de marzo y septiembre en el Instituto de Física de Cantabria, centro mixto CSIC-Universidad de Cantabria, en el grupo de Física Experimental de Altas Energías. Trata fundamentalmente de la medida de la sección eficaz del proceso t¯t con de datos recogidos por el detector CMS del LHC (CERN) por un método novedoso —para este análisis, no de modo general—: las redes neuronales artificiales. El estudio se ha llevado a cabo a partir de los trabajos previos, consolidados, y a la vez en curso, de la misma medida con el método clásico, el análisis secuencial. La implementación de la nueva técnica entonces cumple con varios objetivos: En primer lugar, ensayar una mejora en un sentido concreto a lo que se viene haciendo. En segundo lugar, servir a esto mismo como alternativa y contraste. Y en tercer lugar, y puesto que es un trabajo también académico, funciones didácticas. Máster en Física y Tecnologías Físicas