Search

We present the complete cross-section for the production of unpolarized hadrons in semi-inclusive deep-inelastic scattering up to power-suppressed ${\cal O}(1/Q^2)$ terms in the Wandzura--Wilczek-type approximation which consists in systematically assuming that $\bar{q}gq$--terms are much smaller than $\bar{q}q$--correlators. We compute all twist-2 and twist-3 structure functions and the corresponding asymmetries, and discuss the applicability of the Wandzura--Wilczek-type approximations on the basis of available data. We make predictions that can be tested by data from Jefferson Lab, COMPASS, HERMES, and the future Electron-Ion Collider. The results of this paper can be readily used for phenomenology and for event generators, and will help to improve our understanding of the TMD theory beyond leading twist., Comment: Published in JHEP, 71 pages, 21 figures, references updated, discussion improved

The asymmetry in the azimuthal angle distribution of hadrons produced in unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) carries information on the intrinsic transverse momentum of the quark k → T and on the still unknown Boer-Mulders parton distribution function h 1 ⊥ . Using the data collected in 2016 and 2017 with 160 GeV/c muon beams scattering off a liquid hydrogen target, the COMPASS Collaboration is measuring the azimuthal asymmetries A U U cos ϕ h , A U U cos 2 ϕ h and A L U sin ϕ h for charged hadrons. The preliminary results shown here confirm the strong kinematic dependencies observed in previous measurements conducted by COMPASS, HERMES and CLAS. The contribution from hadrons produced in the decay of vector mesons diffractively produced is also discussed.

The spin asymmetries in SIDIS associated with T-odd TMDs are presented in a light-front quark-diquark model of a proton. To incorporate the effects of the final-state interaction, the light front wave functions are modified to have a phase factor which is essential to have Sivers or Boer-Mulders functions. The Sivers and Boer-Mulder asymmetries are compared with HERMES and COMPASS data.

In this contribution to Light Cone 2014, three average transverse momentum quantities are discussed: the Sivers shift, the dijet imbalance, and the $p_T$ broadening. The definitions of these quantities involve integrals over all transverse momenta that are overly sensitive to the region of large transverse momenta, which conveys little information about the transverse momentum distributions of quarks and gluons inside hadrons. TMD factorization naturally suggests alternative definitions of such integrated quantities, using Bessel-weighting and rapidity cut-offs, with the conventional definitions as limiting cases. The regularized quantities are given in terms of integrals over the TMDs of interest that are well-defined and moreover have the advantage of being amenable to lattice evaluations., 6 pages, no figures, contribution to the proceedings of Light Cone 2014, Raleigh, North Carolina, May 26-30, 2014

Proton transverse-spin azimuthal asymmetries are extracted from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon-nucleon scattering in those four regions of the photon virtuality $Q^2$, which correspond to the four regions of the di-muon mass $\sqrt{Q^2}$ used in the ongoing analysis of the COMPASS Drell-Yan measurements. This allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. Various two-dimensional kinematic dependences are presented for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function. The integrated Sivers asymmetries are found to be positive with an accuracy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics., 13 pages, 6 figures

Title: Study of azimuthal asymmetries in COMPASS Drell-Yan data Author: Bc. Markéta Pešková Department / Institute: Department of Low Temperature Physics Supervisor of the master thesis: M.Sc. Michael Finger, CSc. Abstract: Drell-Yan (DY) process, i.e. a lepton pair production in hadron-hadron interaction, is one of the unique tools to study structure of hadrons. In this thesis we present its theoretical background and its link to description of the nucleon spin structure. The corresponding formalism of the Parton Distribution Functions (PDF) and the Transverse Momentum Dependent Parton Distribution Functions (TMD PDF) is explained in some detail. The fundamental theoretical prediction of a sign change of the T-odd TMDs in the DY and Semi- inclusive DIS (SIDIS) is described. In the following a concise description of the COMPASS apparatus is given with the emphasis on the setup modification needed and implemented for the Drell-Yan measurement performed in 2014 and 2015 with 190 GeV/c2 beam of negative pions and the proton target (polarised in 2015). In the final chapter we present our independent analysis of the DY data taken in 2015. Three azimuthal asymmetries giving access to the different TMD PDF were extracted using the dimuon events from a mass region of 4.3 to 8.5 GeV/c2 . Our results are in agreement...

Çalışmada 402 yazar bulunmaktadır. Bu yazarlardan sadece Bursa Uludağ Üniversitesi mensuplarının girişleri yapılmıştır. We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process e(+) e(-) -> pi pi X based on a data set of 62 pb(-1) at the center-of-mass energy of 3.65 GeV collected with the SESIII detector. These asymmetries can be attributed to the Collins fragmentation function. We observe a nonzero asymmetry, which increases with increasing pion momentum. As our energy scale is close to that of the existing semi-inclusive deep inelastic scattering experimental data, the measured asymmetries are important inputs for the global analysis of extracting the quark transversity distribution inside the nucleon and are valuable to explore the energy evolution of the spin-dependent fragmentation function. National Basic Research Program of China - 2015CB856700 National Natural Science Foundation of China (NSFC) - 11125525 - 11235011 - 11275266 - 11322544 - 11335008 - 11425524 Chinese Academy of Sciences CAS Center for Excellence in Particle Physics (CCEPP) Collaborative Innovation Center for Particles and Interactions (CICPI) National Natural Science Foundation of China (NSFC) - 11179007 - U1232201 - U1332201 Chinese Academy of Sciences - 11179007 - U1232201 - U1332201 - KJCX2-YW-N29 - KJCX2-YW-N45 National 1000 Talents Program of China INPAC Shanghai Key Laboratory for Particle Physics and Cosmology German Research Foundation (DFG) - CRC-1044 Istituto Nazionale di Fisica Nucleare (INFN) Russian Foundation for Basic Research (RFBR) - 14-07-91152 Swedish Research Council European Commission United States Department of Energy (DOE) - DE-FG02-04ER41291 - DE-FG02-05ER41374 - DE-FG02-94ER40823 - DESC0010118 National Science Foundation (NSF) University of Groningen (RuG) Helmholtzzentrum fuer Schwerionenforschung GmbH (GSI), Darmstadt National Research Foundation of Korea - R32-2008-000-10155-0 Türkiye Cumhuriyeti Kalkınma Bakanlığı - DPT2006K-120470

2009/2010 The main topic of this thesis is the measurement of the transverse momentum dependent (TMD) azimuthal asymmetries in the inclusive hadron production in the deep inelastic scattering (DIS). This work has been carried on in the framework of COMPASS, a fixed target experiment at CERN's SPS, which started data taking in 2002. One of the main topic of COMPASS is the study of the nucleon spin structure using high energy (100-200 GeV) muon beam and either transversely and longitudinally polarized proton and deuteron target. Recent developments both from the experimental and theoretical side pointed out the relevance of the transverse spin effects and of new effects, related to the intrinsic transverse momentum of the quark and its correlation with the spin. The nucleon structure, in the non perturbative QCD formalism, can be described at first order, in the collinear approximation, by three parton distribution functions (PDF): the unpolarized PDF, the helicity PDF and the transversity PDF. When including the intrinsic transverse momentum of the quark other 5 PDFs are needed at first order. They are related to the correlation between the transverse momentum of the quark and the spin and are practically unmeasured. The semi inclusive DIS (SIDIS) allows to study all these functions. Indeed the the SIDIS differential cross section, taking into account the beam and target polarization, is characterized by 14 azimuthal modulations in independent linear combination of the nucleon spin angle and of the hadrons angle, as measured with respect to the virtual photon direction. Their amplitudes are related to the structure functions given by the convolution between the new PDFs and the hadron fragmentation functions. In this thesis the measurement of the azimuthal asymmetries which appears in the SIDIS cross section on the unpolarized and longitudinally polarized target. Of particular interest is the information that this measurement give on the Boer-Mulders TMD PDF, which is a very interesting topic. The analysed data have been taken using the 160 GeV positive muon beam on the deuteron target. The target configuration and the spectrometer are optimized for the spin asymmetry measurements and are described in the thesis as well as the data taking. Also, the data processing and the software used for the analysis and the SIDIS data selection are described. The measurement of the azimuthal asymmetries on the longitudinally polarized target have been done using the same data as the one used for the $\Delta$G (the contribution to the nucleon spin of the longitudinal spin of the gluons) measurement. To avoid acceptance effects in the asymmetries extraction, the data collected from the two oppositely polarized target cells (which form the target) have been opportunely combined. Other possible systematic effects have been studied in details and are described in the thesis. \\ The asymmetries have been extracted as functions of the relevant kinematical variables and separately for positive and negative hadrons. The final results, accepted for publication in European Journal C, are compared with the results produced by other experiments and with the calculations of theoretical models of the TMD functions. The measurement of the azimuthal asymmetries which appears in the spin independent part of the SIDIS cross section is more difficult since it cannot benefit from the periodically reversal of the target polarization. The measured hadron azimuthal distributions must be corrected for the possible effects introduced by the apparatus acceptance (geometrical acceptance, detectors and trigger efficiencies). The Monte Carlo simulation of the apparatus has been used to estimate those effects. Extensive studies of the description of the azimuthal acceptance of the apparatus have been done in the whole kinematical domain of interest using different SIDIS events generations. A reliable asymmetries extraction method has been developed and used. A considerable effort has been put into the study and the control of the systematics. Also in this case the asymmetries have been extracted as functions of the relevant kinematical variables and separately for positive and negative hadrons. \\ The strongest measured signals are related to the Cahn effect, which is a kinematical effect proportional to the intrinsic transverse momentum of the quarks, and to the Boer-Mulders TMD PDF, describing the correlation between the intrinsic transverse momentum of the quark and its transverse spin. \\ The results, in particular the kinematical and the charge dependencies of the asymmetries, are interpreted in terms of TMD quantities and higher effects in the non perturbative QCD. The comparisons with the results produced by the other experiments, and with the theoretical predictions are also discussed. XXIII Ciclo 1977

(on behalf of the COMPASS collaboration) The investigation of transverse spin and transverse momentum effects in deep inelastic scattering is one of the key physics programs of the COMPASS collaboration. In the years 2002−2004, COMPASS took 160 GeV muon scattering data on a transversely polarized 6LiD target. In 2007, a transversely polarized NH3 target was used. Three different channels to access the transversity distribution function have been analyzed: the azimuthal distribution of single hadrons, involving the Collins fragmentation function, the azimuthal dependence of the plane containing hadron pairs, involving the two-hadron interference fragmentation function, and the measurement of the transverse polarization of lambda hyperons in the final state. Transverse quark momentum effects in a transversely polarized nucleon have been investigated by measuring the Sivers distribution function. Azimuthal asymmetries in unpolarized semi-inclusive deep-inelastic scattering also give important information on the inner structure of the nucleon, and can be used to estimate both the quark transverse momentum in an unpolarized nucleon and to access the so-far unmeasured Boer-Mulders function. COMPASS has measured these asymmetries in 2004 using spin-averaged 6LiD data., Među glavnim istraživačkim programima suradnje COMPASS je proučavanje poprečnih spinskih i poprečnih impulsnih učinaka u duboko-neelastičnom raspršenju. Tijekom 2002. – 2004., COMPASS je sakupio podatke za muonsko raspršenje na 160 GeV na polariziranoj meti 6LiD. U 2007. rabila se polarizirana meta NH3. Analizirana su tri različita kanala radi dobivanja funkcije raspodjele poprečnosti: azimutalna raspodjela za pojedinačne hadrone koja ovisi o Collinsovoj funkciji lomljenja, azimutalna ovisnost ravnine koja sadrži parove hadrona i u kojoj se javlja interferencija funkcije lomljenja, te poprečna polarizacija lambda hyperona u konačnom stanju. Istraživali su se učinci poprečnih kvarkovskih impulsa u poprečno polarizirnom nukleonu mjerenjem Siversove funkcije. Azimutalne asimetrije u nepolariziranom poluinkluzivnom duboko-neelastičnom raspršenju također daju važne podatke o unutarnjoj strukturi nukleona. Mogu se primijeniti radi procjenjivanja poprečnih impulsa kvarkova u nepolariziranom nukleonu i za određivanje BoerMuldersove funkcije koja dosada nije mjerena. Te je asimetrije odredio COMPASS u 2004. rabeći prosjeke podataka 6LiD mjerenja

We present a summary of a recent workshop held at Duke University on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions. The transverse momentum dependent parton distribution functions (TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation functions, were discussed extensively at the Duke workshop. In this paper, we summarize first the theoretical issues concerning the study of partonic structure of hadrons at a future electron-ion collider (EIC) with emphasis on the TMDs. We then present simulation results on experimental studies of TMDs through measurements of single spin asymmetries (SSA) from semi-inclusive deep-inelastic scattering (SIDIS) processes with an EIC, and discuss the requirement of the detector for SIDIS measurements. The dynamics of parton correlations in the nucleon is further explored via a study of SSA in D (`D) production at large transverse momenta with the aim of accessing the unexplored tri-gluon correlation functions. The workshop participants identified the SSA measurements in SIDIS as a golden program to study TMDs in both the sea and valence quark regions and to study the role of gluons, with the Sivers asymmetry measurements as examples. Such measurements will lead to major advancement in our understanding of TMDs in the valence quark region, and more importantly also allow for the investigation of TMDs in the sea quark region along with a study of their evolution., Comment: 44 pages 23 figures, summary of Duke EIC workshop on TMDs accepted by EPJA

The concept of weighted asymmetries is revisited for semi-inclusive deep inelastic scattering. We consider the cross section in Fourier space, conjugate to the outgoing hadron's transverse momentum, where convolutions of transverse momentum dependent parton distribution functions and fragmentation functions become simple products. Individual asymmetric terms in the cross section can be projected out by means of a generalized set of weights involving Bessel functions. Advantages of employing these Bessel weights are that they suppress (divergent) contributions from high transverse momentum and that soft factors cancel in (Bessel-) weighted asymmetries. Also, the resulting compact expressions immediately connect to previous work on evolution equations for transverse momentum dependent parton distribution and fragmentation functions and to quantities accessible in lattice QCD. Bessel weighted asymmetries are thus model independent observables that augment the description and our understanding of correlations of spin and momentum in nucleon structure., Comment: Matches published version, JHEP style, 36 pages and 2 figures, minor corrections

We report the first measurement of the transverse momentum dependence of double-spin asymmetries in semi-inclusive production of pions in deep-inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Jefferson Lab (JLab). Modulations of single spin asymmetries over the azimuthal angle between lepton scattering and hadron production planes phi have been measured over a wide kinematic range in Bjorken x and virtual photon squared four-momentum Q(2). A significant nonzero sin2 phi single spin asymmetry was observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton.

We investigate the origin of the cos 2 phi azimuthal asymmetry in unpolarized semiinclusive DIS. The contributions to this asymmetry arising from the intrinsic transverse motion of quarks are explicitly evaluated, and predictions for the HERMES and COMPASS kinematic regimes are presented. We show that the effect of the leading-twist Boer-Mulders function h_1^perp(x, k_T^2), which describes a correlation between the transverse momentum and the transverse spin of quarks, is quite significant and may also account for a part of the cos 2 phi asymmetry measured by ZEUS in the perturbative domain., Comment: 11 pages, 7 figures