The study of the spin structure of the nucleon and of the effects rising from the quarks transverse momentum are part of the scientific program of COMPASS, a fixed target experiment at the CERN SPS. The azimuthal asymmetries which appear in the cross-section of SIDIS off unpolarized targets can give insights on the intrinsic momentum structure of the nucleon and on the possible correlation between transverse spin and transverse momentum of the quarks. Here we present the new results for these asymmetries obtained from the COMPASS data collected with a 160 GeV/c positive muon beam impinging on a $^6LiD$ target. The asymmetries are measured for both positive and negative hadrons, and their dependence on several kinematical variable has been studied
The production of vector mesons in SIDIS is a particularly interesting channel to study the polarized fragmentation and related phenomena. Preliminary COMPASS results for the first measurement of inclusive $ρ^0$ Collins and Sivers transverse-spin asymmetries are presented here for the first time. The analysis is based on the data-set collected by COMPASS in $2010$ using a $160\, \rm{GeV}/c$ $μ^+$ beam and a transversely polarized $NH_3$ target. The asymmetries are extracted as function of Bjorken-$x$, of the total transverse momentum of the oppositely charged hadron pair and of the fraction of…
Revisiting Unidentified Charged-Hadron Fragmentation Functions with Modern COMPASS SIDIS Multiplicities
School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM)（粒子与加速器学院，基础科学研究院）；AGH University, Faculty of Physics and Applied Computer Science（AGH科技大学，物理与应用计算机科学学院）；PRISMA ++ Cluster of Excellence, Institut für Physik, Johannes Gutenberg-Universität Mainz（PRISMA++卓越集群，物理研究所，约翰内斯·古腾堡美因茨大学）；Institut für Theoretische Physik, Universität Münster（理论物理研究所，明斯特大学）
Preliminary results obtained by the COMPASS experiment for longitudinal-spin-dependent azimuthal asymmetries in single-hadron muoproduction off protons are presented for the first time. The analysis was carried out on the full data sample collected by COMPASS with longitudinally polarized proton ($NH_3$) target in 2007 and 2011 using 160~\gvc and 200~\gvc muon beams, correspondingly. Within QCD parton model approach extracted asymmetries are giving access to the specific convolutions of certain transverse-momentum-dependent \textit{twist-2} and \textit{higher twist} parton distribution functio…
Modern Determination of Pion and Kaon Fragmentation Functions from SIA and High-Precision COMPASS SIDIS Multiplicities
School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM)（粒子与加速器学院，基础科学研究院）；AGH University, Faculty of Physics and Applied Computer Science（AGH科技大学，物理与应用计算机科学系）；PRISMA ++ Cluster of Excellence, Institut für Physik, Johannes Gutenberg-Universität Mainz（PRISMA ++ 卓越集群，物理学研究所，约翰内斯·古腾堡美因茨大学）；Institut für Theoretische Physik, Universität Münster（理论物理研究所，明斯特大学）
Since 2005, measurements of Collins and Sivers asymmetries from the HERMES and COMPASS experiments have allowed to assess that the transversity and the Sivers PDFs are different from zero and measurable in semi-inclusive DIS on transversely polarised targets. Most of the data were collected on proton targets, only small event samples were collected in the early phase of the COMPASS experiment on a deuteron ($^6$LiD) target and more recently at JLab, on $^3$He, so that the $d$-quark and the sea-quarks PDFs are much more poorly known than the $u$-quark PDFs. This constitutes an important limitat…
The exploration of the transverse spin structure of the nucleon by measuring spin (in)dependent azimuthal asymmetries in semi-inclusive DIS (SIDIS) and in Drell-Yan processes is one of the main objectives of the COMPASS experiment at CERN (SPS, M2 beamline). During the first phase of the experiment (2002-2011) a series of SIDIS measurements were performed, using a longitudinally polarized muon beam impinging on transversely polarized $^6$LiD or NH$_3$ targets. As a part of the COMPASS-II programme, in 2015 and 2018 the experiment performed Drell-Yan measurements with a $π^-$ beam interacting w…
The COMPASS Collaboration is measuring the asymmetries in the azimuthal distributions of positive and negative hadrons produced in Deep Inelastic Scattering (DIS) on unpolarized protons. The data have been collected in 2016 and 2017 with a 160 GeV/$c$ muon beam scattering off a liquid hydrogen target. The amplitudes of three modulations, $A_{UU}^{\cosϕ_h}$, $A_{UU}^{\cos 2ϕ_h}$ and $A_{LU}^{\sinϕ_h}$ are measured as function of the Bjorken variable $x$, of the fraction of virtual photon energy carried by the hadron $z$, and of the hadron transverse momentum with respect to the virtual photon $…
The measurement of azimuthal modulations in hadron leptoproduction on unpolarized nucleons allows to get information on the intrinsic transverse momentum $\langle k_T^2 \rangle$ of quarks in a nucleon through both the Cahn effect and the Boer-Mulders function. We have compared the azimuthal asymmetries in the cross section of $160\, \rm{GeV}/c$ muons scattered off an unpolarised deuteron target as measured by COMPASS with a Monte Carlo program, based on the ${}^3P_0$ model of quark anti-quark pair production at string breaking, which accounts for the Cahn effect. Large differences have been ob…
COMPASS is a fixed-target experiment in operation at the CERN North Area (SPS, M2 beam-line) since 2002. An important part of the broad physics programme of the experiment is dedicated to the exploration of the transverse spin-structure of the nucleon studying target transverse spin dependent azimuthal asymmetries (TSAs) arising in the Semi-Inclusive DIS (SIDIS) and Drell-Yan (DY) cross-sections. In addition to those measurements, COMPASS has recently studied also the TSAs weighted by powers of the hadron transverse momentum (in SIDIS) and virtual photon transverse momentum, $q_T$ (in DY). In …
COMPASS final results on multiplicities of charged hadrons and of identified pions and kaons produced in the deep inelastic muon scattering off an isoscalar target are presented and compared to HERMES results. Measurements are done in bins of x, y and z in a wide kinematic range. The hadron and pion data show a good agreement with (N)LO QCD expectations. The kaon data are long awaited for since they are needed to extract kaon fragmentation functions, a crucial ingredient in solving the strange quark polarisation puzzle. COMPASS results for kaons differ from the expectations of the old NLO DSS …
Partonic Transverse Motion in Unpolarized Semi-Inclusive Deep Inelastic Scattering Processes
分析了部分子横向运动在非极化半包容深度非弹性散射（SIDIS）过程中的作用。施加适当的运动学条件，我们发现一些限制，固定的上限范围内允许的k_perp值。我们表明，应用这些额外的要求的部分子运动学，我们得到不同的结果相对于通常的唯象方法的基础上的高斯涂抹与分析积分在无限范围内的k_perp值。这些变化对某些观测值特别有意义，例如< cos phi_h >未极化SIDIS截面的方位角调制或最终检测到的强子的平均横向动量。
Phenomenological Estimate for the Longitudinal Unpolarized Structure Function in Semi-inclusive Deep Inelastic Scattering
Università di Pavia（帕维亚大学）；INFN, Sez. di Pavia（意大利国家核物理研究所帕维亚分部）；Université Paris-Saclay - CEA - IRFU（巴黎-萨克雷大学法国原子能委员会IRFU）；Penn State University Berks（宾夕法尼亚州立大学伯克斯分校）；Old Dominion University（老道明大学）；Jefferson Lab（杰斐逊实验室）
We investigate the theoretical framework of the $\cos 2ϕ$ azimuthal asymmetry contributed by the coupling of two Boer-Mulders functions in the dilepton production unpolarized $πp$ Drell-Yan process by applying the transverse momentum dependent factorization at leading order. We adopt the model calculation results of the unpolarized distribution function $f_1$ and Boer-Mulders function $h_1^\perp$ of pion meson from the light-cone wave functions. We take into account the transverse momentum evolution effects for both the distribution functions of pion and proton by adopting the existed extracti…
In 2016 and 2017 COMPASS has collected a considerable amount of deep inelastic scattering events with a 160 GeV/c muon beam and a liquid hydrogen target. An analysis of 4 % of these data has allowed to extract preliminary results on the amplitudes of three azimuthal modulations, $A_{UU}^{\cosϕ_h}$, $A_{UU}^{\cos2ϕ_h}$ and $A_{LU}^{\sinϕ_h}$. The first two are particularly important since they carry information on the intrinsic transverse momentum $\vec{k}_T$ of the quarks and on the correlations between the quark spin and $\vec{k}_T$, expressed by the Boer-Mulders TMD PDFs. They show strong ki…
We make a systematic study of $Λ$ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as $e^-N\to e^-ΛX$ and $e^+e^-\toΛh X$. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions, i.e., the longitudinal direction along the hyperon momentum, the normal direction of the production plane, and the transverse direction in the production plane. We present the parton model results at the leading twist and leadi…
SIDIS-RC EvGen is a C++ standalone Monte-Carlo event generator for studies of semi-inclusive deep inelastic scattering (SIDIS) processes at medium to high lepton beam energies. In particular, the generator contains binary and library components for generating SIDS events and calculating cross sections for unpolarized or longitudinally polarized beam and unpolarized, longitudinally or transversely polarized target. The structure of the generator incorporates transverse momentum-dependent parton distribution and fragmentation functions, whereby we obtain multi-dimensional binned simulation resul…
We study the single longitudinal-spin asymmetry of dihadron production in semi-inclusive deep inelastic scattering process. We consider the collinear picture in which the transverse momentum of the final-state hadron pair is integrated out, such that the $\sin ϕ_R$ azimuthal asymmetry arises from the coupling $h_L\, H_{1}^{\sphericalangle}$ as well as the coupling $g_1 \,\widetilde{G}^{\sphericalangle}$. We calculate the unknown twist-3 dihadron fragmentation function $\widetilde{G}^{\sphericalangle}$ using a spectator model which is successful in describing the dihadron production in the unpo…
The COMPASS experiment at CERN, as part of its programme addresses the exploration of the transverse spin structure of the nucleon by measuring spin (in)dependent azimuthal asymmetries in semi-inclusive DIS and, recently, also in Drell-Yan processes. Between 2002 and 2010 COMPASS performed a series of SIDIS measurements, using a longitudinally polarized muon beam impinging on transversely polarized $^6LiD$ or $NH_3$ targets. Drell-Yan measurements with a $π^-$ beam interacting with a transversely polarized $NH_3$ target started with the 2015 run and will be continued in 2018. In this Letter th…
The study of $Λ$ polarization in Semi-Inclusive Deep Inelastic Scattering (SIDIS) with a transversely polarized target has often been suggested as a privileged way to access transversity, as the initial quark polarization can be transmitted to the hyperon and then observed via its weak decay. COMPASS measured the $Λ$ transversity-induced polarization as a function of Bjorken $x$, of the fraction $z$ of the longitudinal momentum of the fragmenting quark carried by the $Λ$ and of the $Λ$ transverse momentum $P_T$. The results are compatible with zero in all regions of phase space. Under the hypo…
Muon pairs created in the Drell-Yan process of a negative pion beam of 190 GeV/c momentum impinging on a transversely polarised NH$_3$ target were detected with the COMPASS spectrometer at CERN in 2015. In addition to the extraction of the transverse spin asymmetries (TSAs) from these data, a complementary analysis of the TSAs weighted by powers of the dimuon momentum $q_T$ has been performed and is presented in this paper. In the transverse momentum dependent parton distribution functions (TMD PDFs) formalism, the $q_T$-weighted TSAs can be interpreted in terms of products of the TMD PDFs of …
The COMPASS Collaboration measured the transverse momentum dependent multiplicities of charged hadrons produced in Deep Inelastic Scattering (DIS) off unpolarized protons. Complementing previous COMPASS measurements obtained with an isoscalar target, the data have been collected in 2016 and 2017 with 160 GeV/$c$ muon beams and a liquid hydrogen target. The multiplicities are studied as a function of the square of the hadron transverse momentum with respect to the virtual photon direction $P_{hT}^2$ in bins of the Bjorken variable $x$, of the photon virtuality $Q^2$ and of the fraction $z$ of t…
Proposal for measuring new transverse momentum dependent parton distributions $g_{1T}$ and $h_{1L}^\perp$ through semi-inclusive deep inelastic scattering
The aim of this Thesis is to contribute to the understanding of the nucleon structure through the study of two observables accessible in Semi-Inclusive Deep Inelastic Scattering (SIDIS) of high energy leptons off unpolarized protons: the transverse-momentum distributions and the amplitudes of the modulations in the azimuthal angle of the final state hadrons, the latter referred to as "azimuthal asymmetries". They give relevant information on the transverse momentum of the partons inside the nucleon and on the Boer-Mulders TMD PDF. This Thesis summarizes the work done in this direction during m…
