Collins and Sivers asymmetries for pions and kaons in muon-deuteron DIS
The COMPASS Collaboration, M. Alekseev, V. Yu. Alexakhin, Yu. Alexandrov, G. D. Alexeev, A. Amoroso, A. Arbuzov, B. Badełek, F. Balestra, J. Ball, J. Barth, G. … 展开作者
The COMPASS Collaboration, M. Alekseev, V. Yu. Alexakhin, Yu. Alexandrov, G. D. Alexeev, A. Amoroso, A. Arbuzov, B. Badełek, F. Balestra, J. Ball, J. Barth, G. Baum, Y. Bedfer, C. Bernet, R. Bertini, M. Bettinelli, R. Birsa, J. Bisplinghoff, P. Bordalo, F. Bradamante, A. Bravar, A. Bressan, G. Brona, E. Burtin, M. P. Bussa, A. Chapiro, M. Chiosso, A. Cicuttin, M. Colantoni, S. Costa, M. L. Crespo, S. Dalla Torre, T. Dafni, S. Das, S. S. Dasgupta, R. De Masi, N. Dedek, O. Yu. Denisov, L. Dhara, V. Diaz, A. M. Dinkelbach, S. V. Donskov, V. A. Dorofeev, N. Doshita, V. Duic, W. Dünnweber, P. D. Eversheim, A. V. Efremov, W. Eyrich, M. Faessler, V. Falaleev, A. Ferrero, L. Ferrero, M. Finger, M. Finger, H. Fischer, C. Franco, J. Franz, J. M. Friedrich, V. Frolov, R. Garfagnini, F. Gautheron, O. P. Gavrichtchouk, R. Gazda, S. Gerassimov, R. Geyer, M. Giorgi, B. Gobbo, S. Goertz, A. M. Gorin, S. Grabmüller, O. A. Grajek, A. Grasso, B. Grube, R. Gushterski, A. Guskov, F. Haas, J. Hannappel, D. von Harrach, T. Hasegawa, J. Heckmann, S. Hedicke, F. H. Heinsius, R. Hermann, C. Heß, F. Hinterberger, M. von Hodenberg, N. Horikawa, S. Horikawa, N. d'Hose, C. Ilgner, A. I. Ioukaev, S. Ishimoto, O. Ivanov, Yu. Ivanshin, T. Iwata, R. Jahn, A. Janata, P. Jasinski, R. Joosten, N. I. Jouravlev, E. Kabuß, D. Kang, B. Ketzer, G. V. Khaustov, Yu. A. Khokhlov, Yu. Kisselev, F. Klein, K. Klimaszewski, S. Koblitz, J. H. Koivuniemi, V. N. Kolosov, E. V. Komissarov, K. Kondo, K. Königsmann, I. Konorov, V. F. Konstantinov, A. S. Korentchenko, A. Korzenev, A. M. Kotzinian, N. A. Koutchinski, O. Kouznetsov, A. Kral, N. P. Kravchuk, Z. V. Kroumchtein, R. Kuhn, F. Kunne, K. Kurek, M. E. Ladygin, M. Lamanna, J. M. Le Goff, A. A. Lednev, A. Lehmann, S. Levorato, J. Lichtenstadt, T. Liska, I. Ludwig, A. Maggiora, M. Maggiora, A. Magnon, G. K. Mallot, A. Mann, C. Marchand, J. Marroncle, A. Martin, J. Marzec, F. Massmann, T. Matsuda, A. N. Maximov, W. Meyer, A. Mielech, Yu. V. Mikhailov, M. A. Moinester, A. Mutter, A. Nagaytsev, T. Nagel, O. Nähle, J. Nassalski, S. Neliba, F. Nerling, S. Neubert, D. P. Neyret, V. I. Nikolaenko, K. Nikolaev, A. G. Olshevsky, M. Ostrick, A. Padee, P. Pagano, S. Panebianco, R. Panknin, D. Panzieri, S. Paul, B. Pawlukiewicz-Kaminska, D. V. Peshekhonov, V. D. Peshekhonov, G. Piragino, S. Platchkov, J. Pochodzalla, J. Polak, V. A. Polyakov, J. Pretz, S. Procureur, C. Quintans, J. -F. Rajotte, S. Ramos, V. Rapatsky, G. Reicherz, D. Reggiani, A. Richter, F. Robinet, E. Rocco, E. Rondio, A. M. Rozhdestvensky, D. I. Ryabchikov, V. D. Samoylenko, A. Sandacz, H. Santos, M. G. Sapozhnikov, S. Sarkar, I. A. Savin, P. Schiavon, C. Schill, L. Schmitt, P. Schönmeier, W. Schröder, O. Yu. Shevchenko, H. -W. Siebert, L. Silva, L. Sinha, A. N. Sissakian, M. Slunecka, G. I. Smirnov, S. Sosio, F. Sozzi, A. Srnka, F. Stinzing, M. Stolarski, V. P. Sugonyaev, M. Sulc, R. Sulej, V. V. Tchalishev, S. Tessaro, F. Tessarotto, A. Teufel, L. G. Tkatchev, G. Venugopal, M. Virius, N. V. Vlassov, A. Vossen, R. Webb, E. Weise, Q. Weitzel, R. Windmolders, S. Wirth, W. Wiślicki, H. Wollny, K. Zaremba, M. Zavertyaev, E. Zemlyanichkina, J. Zhao, R. Ziegler, A. Zvyagin
备注：
16 pages, 9 figures, added author Efremov, calculated pure kaon asymmetries instead of those for experimental kaon/pion mixture (mainly error affected)
The measurements of the Collins and Sivers asymmetries of identified hadrons produced in deep-inelastic scattering of 160 GeV/c muons on a transversely polarised 6LiD target at COMPASS are presented. The results for charged pions and charged and neutral kaons correspond to all data available, which were collected from 2002 to 2004. For all final state particles both the Collins and Sivers asymmetries turn out to be small, compatible with zero within the statistical errors, in line with the previously published results for not identified charged hadrons, and with the expected cancellation between the u- and d-quark contributions.
The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results nicely support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fr…
Azimuthal single-spin asymmetries (SSA) in semi-inclusive electroproduction of pi-mesons and charged K-mesons in deep-inelastic scattering of positrons and electrons on a transversely polarised hydrogen target were observed. Significant SSA amplitudes for both the Collins and the Sivers mechanism are presented for the full data set recorded with transverse target polarisation at the HERMES experiment.
New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised 6LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with …
COMPASS is a fixed-target experiment on the SPS M2 beamline at CERN. Its LiD target can be polarised both longitudinally and transversally with respect to the longitudinally polarised 160 GeV/c muon beam. Approximately 20% of the beam-time in 2002, 2003 and 2004 was spent in the transverse configuration, allowing the first measurement of both the Collins and Sivers asymmetries on a deuterium target. First results from the the transverse data of the COMPASS run in 2002 are reported here.
COMPASS is a fixed target experiment presently running at CERN. In 2002, 2003, and 2004 the experiment used a 160 GeV polarized muon beam coming from SPS and scattered off a $^6$LiD target. The nucleons in the target can be polarized either longitudinally or transversely with respect to the muon beam and 20% of the running time has been devoted to transverse polarization. From the transverse polarization data collected in 2002, which correspond to a total integrated luminosity of about 200 pb$^{-1}$, the Collins and the Sivers asymmetries have been determined separately and the preliminary res…
The study of transverse spin and transverse momentum effects is an important part of the scientific program of COMPASS, a fixed target experiment at the CERN SPS taking data since 2002. The studies are carried on by measuring the hadrons produced in deep inelastic scattering (DIS) of 160 GeV/c muons off different targets. Among the possible asymmetries in the hadron azimuthal distributions, particularly interesting are the Collins and Sivers asymmetries which the COMPASS Collaboration has measured using transversely polarised deuteron and proton targets. The new results for charged pions and k…
In the list of the main items studied by the CERN COMPASS experiment there are the transverse spin and momentum effects visible in the azimuthal distributions of hadrons produced in the deep inelastic scattering. In the years 2002-2004 COMPASS has collected data with a 6LiD target with the polarization oriented transversely with respect to the muon beam direction for about 20% of the running time; in 2007, COMPASS has used for the first time a proton NH_3 target with the data taking time equally shared between longitudinal and transverse polarization of the target. After reviewing the results …
In semi-inclusive DIS of polarized leptons on a transversely polarized target eight azimuthal modulations appear in the cross-section. Within QCD parton model four azimuthal asymmetries can be interpreted at leading order, two of them being the already measured Collins and Sivers asymmetries. The other two leading twist asymmetries, related to different transverse momentum dependent quark distribution functions, and also additional four asymmetries which can be interpreted as twist-three contributions have been measured for the first time at COMPASS, using a 160 GeV/c longitudinally polarized …
The study of transverse spin and transverse momentum effects is an important part of the scientific program of COMPASS, a fixed target experiment at the CERN SPS. For these studies a 160 GeV/c momentum muon beam is scattered on a transversely polarized nucleon target, and the scattered muon and the forward going hadrons produced in DIS processes are reconstructed and identified in a magnetic spectrometer. The measurements have been performed on a deuteron target in 2002, 2003 and 2004, and on a proton target in 2007 and 2010. The results obtained for the Collins and Sivers asymmetries from the…
We present predictions and projections for hadron-in-jet measurements and electron-jet azimuthal correlations at the future Electron-Ion Collider (EIC). These observables directly probe the three-dimensional (3D) structure of hadrons, in particular, the quark transversity and Sivers parton distributions and the Collins fragmentation functions. We explore the feasibility of these experimental measurements by detector simulations and discuss detector requirements. We conclude that jet observables have the potential to enhance the 3D imaging EIC program.
One of the important objectives of the COMPASS experiment (SPS, CERN) \cite{Abbon:2007pq} is the exploration of the transverse spin structure of the nucleon via spin dependent azimuthal asymmetries in single-hadron production in deep inelastic scattering of polarized leptons off transversely polarized targets. For this purpose a series of measurements were made in COMPASS, using 160 GeV/c longitudinally polarized muon beam and transversely polarized $^6LiD$ (in 2002, 2003 and 2004) and $NH_3$ (in 2007 and 2010) targets. In the past few years considerable theoretical interest and experimental e…
First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarized 6-LiD target are presented. The data were taken in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.
COMPASS is a fixed-target high energy physics experiment at the SPS at CERN \cite{Abbon:2007pq}. One of the important objectives of the experiment is the exploration of the transverse spin structure of the nucleon via spin dependent azimuthal asymmetries in single-hadron production in deep inelastic scattering of polarized leptons off transversely polarized target. For this purpose a series of measurements were made in COMPASS, using 160 GeV/c longitudinally polarized muon beam and transversely polarized $^6LiD$ (in 2002, 2003 and 2004) and $NH_3$ (in 2007 and 2010) targets. Till now main atte…
We extend the improved Collins-Soper-Sterman (iCSS) $W+Y$ construction recently presented in~\cite{Collins:2016hqq} to the case of polarized observables, where we focus in particular on the Sivers effect in semi-inclusive deep-inelastic scattering. We further show how one recovers the expected leading-order collinear twist-3 result from a (weighted) $q_T$-integral of the differential cross section. We are also able to demonstrate the validity of the well-known relation between the (TMD) Sivers function and the (collinear twist-3) Qiu-Sterman function within the iCSS framework. This relation al…
New results on single spin asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised LiD target are presented. The data were taken in the years 2002, 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Preliminary results are given for the Sivers asymmetry and for all the three ``quark polarimeters'' presently used in COMPASS to measure the transversity distributions. The Collins and the Sivers asymmetries for charged hadrons turn out to be compatible with zero, within the small (~1%) statistical errors, …
STAR has observed sizable transverse single-spin asymmetries for inclusive pi^0 production at forward rapidity in p+p collisions at sqrt{s}=200 GeV. These asymmetries may arise from either the Sivers or Collins effect. Studies are underway during the current RHIC run to elucidate the dynamics that underlie these single-spin asymmetries. Additional measurements are underway to search for the Sivers effect in mid-rapidity di-jet production.
Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise.
COMPASS is a fixed target experiment at CERN investigating the spin structure of the nucleon and performing hadron spectroscopy. The transverse spin structure of the nucleon is studied in semi-inclusive deep-inelastic scattering of 160 GeV/c muons off a transversely polarized proton or deuteron target. In 2002-2005, a transversely polarized 6LiD, and in 2007 a transversely polarized NH3 target were used. To get access to the transversity distribution, different single-spin asymmetries have been measured: the Collins asymmetry, the hadron-pair asymmetry and the transverse lambda polarization. I…
Measurements by the STAR collaboration of the cross section and transverse single spin asymmetry (SSA) of neutral pion production at large Feynman x (x_F) in pp-collisions at \sqrt{s}=200 GeV were reported previously. The x_F dependence of the asymmetry can be described by phenomenological models that include the Sivers effect, Collins effect or higher twist contributions in the initial and final states. Discriminating between the Sivers and Collins effects requires one to go beyond inclusive π^0 measurements. For the 2008 run, forward calorimetry at STAR was significantly extended. The large …
HERMES has measured azimuthal single-spin asymmetries of pions and charged kaons produced in deep-inelastic scattering of electrons and positrons off a transversely polarized hydrogen target. These asymmetries provide information about the Collins and Sivers mechanisms, which are signals for the transverse parton distribution function h_1^q in convolution with the Collins fragmentation function H_1^{\perp,q}, and of the Sivers distribution function f_{1T}^{\perp,q} with the spin-averaged fragmentation function D_q^h, respectively. Furthermore, both the momentum and helicity distributions of th…
We investigate the Sivers asymmetry in the pion-induced single polarized Drell-Yan process in the theoretical framework of the transverse momentum dependent factorization up to next-to-leading logarithmic order of QCD. Within the TMD evolution formalism of parton distribution functions, the recently extracted nonperturbative Sudakov form factor for the pion distribution functions as well as the one for the Sivers function of the proton are applied to numerically estimate the Sivers asymmetry in the $π^- p$ Drell-Yan at the kinematics of the COMPASS at CERN. In the low $b$ region, the Sivers fu…
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…
Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion ($ϕ$) and the target spin axis ($ϕ_S$) about the virtual photon direction and relative to the lepton scattering plane. The extracted Fourier component $\cmpi$ is a signal of the previously unmeasured quark transversity distribution, in conjunction with the so-called Collins fragmentation function, also unknown. The Fourier component $\smpi$ of th…
Azimuthal correlations in two hadron production in deep inelastic scattering of unpolarized leptons off transversely polarized nucleon are discussed. Specifically, a simple approach for accessing ratios of structure functions corresponding to Sivers effect and transversity induced single spin azimuthal asymmetries to unpolarized structure functions is presented. This approach is then applied to a sample pseudo-data generated by a modified version of the LEPTO Monte Carlo event generator that includes the Sivers effect. Using this data it is shown, that the azimuthal correlations in the Sivers-…
Azimuthal single-spin asymmetries (SSA) in semi-inclusive electroproduction of charged pions in deep-inelastic scattering (DIS) of positrons on a transversely polarised hydrogen target are presented. Azimuthal moments for both the Collins and the Sivers mechanism are extracted. In addition the subleading-twist contribution due to the transverse spin component from SSA on a longitudinally polarised hydrogen target is evaluated.
The COMPASS experiment is a fixed target experiment at the CERN SPS using muon and hadron beams for the investigation of the spin structure of the nucleon and hadron spectroscopy. The main objective of the muon physics program is the study of the spin of the nucleon in terms of its constituents, quarks and gluons. COMPASS has accumulated data during 6 years scattering polarized muons off a longitudinally or a transversely polarized deuteron (6LiD) or proton (NH3) target. Results for the gluon polarization are obtained from longitudinal double spin cross section asymmetries using two different …
Measurements of single-spin asymmetries for semi-inclusive electro-production of pions and kaons in deep-inelastic scattering with transverse target polarization open a new window on the transverse quark and gluon structure of the nucleon. The first experimental results from such measurements as well as experiments in progress are discussed. Properties of the spin-dependent Collins fragmentation function and prospects for extracting the transversity are reviewed and evidence for nonzero Sivers asymmetries as manifestations of quark orbital angular momentum is evaluated.
Transverse spin physics is an important part of the scientific programme of the COMPASS experiment at CERN. The analysis of the data taken with the target polarized orthogonally to the 160 GeV/c muon beam momentum has allowed to measure for the first time the Collins and Sivers asymmetries of the deuteron. Both for the positive and the negative hadrons produced in semi-inclusive DIS the measured asymmetries are small and, within errors, compatible with zero. New results for charged pions and kaons are presented here.
Azimuthal single-spin asymmetries of lepto-produced pions and charged kaons were measured on a transversely polarized hydrogen target. Evidence for a naive-T-odd, transverse-momentum-dependent parton distribution function is deduced from non-vanishing Sivers effects for pi+, pi0, and K+, K-, as well as in the difference of the pi+ and pi- cross sections.
Measurements by the STAR collaboration of neutral pion production at large Feynman x (x_F) in the first polarized proton collisions at $\sqrt{s}=200$ GeV were reported previously. Cross sections measured at $η=3.3$, 3.8 and 4.0 are found to be consistent with next-to-leading order perturbative QCD calculations. The analyzing power is consistent with zero at negative x_F and at positive x_F up to ~0.3, then grows more positive with increasing x_F. This behavior can be described by phenomenological models including the Sivers effect, the Collins effect or higher twist contributions in the initia…
We study single spin asymmetries at one-loop accuracy in semi-inclusive DIS with a transversely polarized hadron in the initial state. Two measurable spin observables are predicted in the framework of QCD collinear factorization. One of the spin observables is the Sivers weighted asymmetry, another one is the Collins weighted asymmetry. The prediction takes a form of convolutions of perturbative coefficient functions and nonperturbative functions, which are twist-2 transversity distributions, twist-3 parton distributions, twist-2- and twist-3 parton fragmentation functions. These nonperturbati…
The study and characterisation of transverse-momentum-dependent distribution functions (TMDs) is a major goal of the Electron-Ion Collider (EIC) physics programme. The study of gluon TMDs poses a greater challenge than for quark TMDs in DIS measurements, as gluons do not directly couple to photons. The study of D meson pairs has been proposed to provide access to gluon TMDs, but is demanding due to the rarity of D production. Here, we discuss the feasibility of such a measurement, and touch upon wider issues to be considered when measuring TMDs at the EIC.
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 SIDIS transverse spin asymmetries weighted with powers of $P_T$, the hadron transverse momentum in the $γN$ reference system,have been introduced already twenty years ago and are considered quite interesting. While the amplitudes of the modulations in the azimuthal distribution of the hadrons are the ratios of convolutions over transverse momenta of the transverse--momentum dependent parton distributions and of the corresponding fragmentation functions, and can be evaluated analytically only making assumptions on the transverse--momentum dependence of these functions, the weighted asymmetr…
The study of the Sivers effect, describing correlations between the transverse polarization of the nucleon and its constituent (unpolarized) parton's transverse momentum, has been the topic of a great deal of experimental, phenomenological and theoretical effort in recent years. Semi-inclusive deep inelastic scattering measurements of the corresponding single spin asymmetries (SSA) at the upcoming CLAS12 experiment at JLab and the proposed Electron-Ion Collider will help to pinpoint the flavor structure and the momentum dependence of the Sivers parton distribution function describing this effe…
The Sivers effect in polarized SIDIS can be measured in two hadron production as sine modulations involving the azimuthal angles $φ_T$ and $φ_R$ of both the total and the relative transverse momenta of the hadron pair, complementary to the conventional single hadron studies. In this talk we briefly present the results obtained in our recent work [1] and [2]. We also present the leading order parton model expression for the two hadron SIDIS cross section for different choices of the relative transverse momentum that dismiss the seeming contradiction of our results with previous work. Finally, w…
The Sivers effect in single hadron semi-inclusive deep inelastic scattering (DIS) on a transversely polarized nucleon describes the modulation of the cross section with the sine of the azimuthal angle between the produced hadron's transverse momentum and the nucleon spin ($\boldsymbol{P}_h$ and $φ_S$ respectively). This effect is attributed to the so-called Sivers parton distribution function of the nucleon. We employ a simple phenomenological parton model to derive the relevant cross section for two-hadron production in semi-inclusive deep inelastic scattering including the Sivers effect. We …
We report the first measurement of target single spin asymmetries in the semi-inclusive $^3{He}(e,e'π^\pm)X$ reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.14 $< x <$ 0.34 with 1.3 $<Q^2<$ 2.7 GeV$^2$. The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The extracted $π^\pm$ Collins moments for $^3$He are consistent with zero, except for the $π^+$ moment at $x=0.34$, which deviates from zero by 2.3$σ$. While the $π^-$ Sivers moments are consis…
Northwestern University（西北大学）；Stony Brook University（纽约州立大学石溪分校）；Beijing Normal University（北京师范大学）；Institute of Modern Physics, Chinese Academy of Science（中国科学院近代物理研究所）
