SIDIS transverse spin azimuthal asymmetries at COMPASS: Multidimensional analysis

Exploration of transverse spin structure of the nucleon via study of the spin (in)dependent azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan (DY) reactions is one of the main aspects of the broad physics program of the COMPASS experiment (CERN, Switzerland). In past decade COMPASS has collected a considerable amount of polarized deuteron and proton SIDIS data, while recent 2014 and 2015 runs were dedicated to the Drell-Yan measurements. Results on SIDIS azimuthal effects provided so far by COMPASS play an important role in general understanding of the three-dimensional nature of the nucleon. Giving access to the entire "twist-2" set of transverse momentum dependent (TMD) parton distribution functions (PDFs) and fragmentation functions (FFs) COMPASS data are being widely used in phenomenological analyses and experimental data fits. Recent unique and first ever x-$Q^{2}$-z-pT multidimensional results for transverse spin asymmetries obtained by COMPASS serve as a direct and unprecedented input for one of the hottest topics in the field of spin-physics: the TMD $Q^{2}$-evolution related studies. In addition, extraction of the Sivers and all other azimuthal effects from first ever polarized Drell-Yan data collected recently by COMPASS will reveal another side of the spin-puzzle clarifying the link between SIDIS and Drell-Yan branches. This will be a unique possibility to test predicted universality and key-features of TMD PDFs using essentially the same experimental setup and exploring the same kinematical domain. In this review main focus will be given to the very recent results from COMPASS multi-dimensional analysis of transverse spin asymmetries and to the physics aspects of COMPASS polarized Drell-Yan program.Comment: 11 pages, 9 figures, QCD Evolution 2015 conference (QCDEV2015), 26-30 May 2015, Jefferson Lab (JLAB), Newport News Virginia, USA. arXiv admin note: substantial text overlap with arXiv:1511.09093, arXiv:1504.01599, arXiv:1512.0677

Transverse spin azimuthal asymmetries at COMPASS: SIDIS Multi-D analysis & Drell-Yan

COMPASS is a high-energy physics experiment operating on the M2 beam line at the SPS at CERN. Using high energy muon and hadron beams the experiment covers broad range of physics aspects in the field of the hadron structure and spectroscopy. One of the important objectives of the COMPASS experiment is the exploration of transverse spin structure of the nucleon via study of spin (in)dependent azimuthal asymmetries with semi-inclusive deep inelastic scattering (SIDIS) processes and starting from 2014 also with Drell-Yan (DY) reactions. Experimental results obtained by COMPASS for azimuthal effects in SIDIS play an important role in the general understanding of the three-dimensional nature of the nucleon. Giving access to the entire "twist-2" set of transverse momentum dependent (TMD) parton distribution functions (PDFs) and fragmentation functions (FFs) COMPASS data trigger constant theoretical interest and are being widely used in phenomenological analyses and global data fits. In particular, unique x-$Q^{2}$-z-pT multidimensional results for transverse spin asymmetries recently obtained by COMPASS will serve as a direct and unprecedented input for TMD $Q^{2}$-evolution related studies, one of the hottest topics in the field of spin-physics. In addition, measurement of the Sivers and all other azimuthal effects in polarized Drell-Yan at COMPASS will reveal another side of the spin-puzzle providing a link between SIDIS and Drell-Yan branches. This will be a unique possibility to test universality and key-features of TMD PDFs using essentially the same experimental setup and exploring the same kinematical domain. In this review main focus will be given to the very recent results obtained by the collaboration for multi-dimensional transverse spin asymmetries and to the physics aspects of COMPASS polarized Drell-Yan program.Comment: 9 pages, 8 figures, XVI Workshop on High Energy Spin Physics, DSPIN-15, Dubna, Russia, September 8 - 12, 2015. arXiv admin note: substantial text overlap with arXiv:1504.01599, arXiv:1511.09093, arXiv:1512.0659

Transverse spin asymmetries at COMPASS: beyond Collins and Sivers effects

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 efforts were focused on the study of Collins and Sivers transverse spin asymmetries. The experimental results obtained so far play an important role in the general understanding of the three-dimensional nature of the nucleon in terms of transverse momentum dependent parton distribution functions. In addition to these two measured leading-twist effects, the SIDIS cross-section includes six more target transverse spin dependent azimuthal asymmetries, which have their own well defined leading or higher-twist interpretation in terms of QCD parton model. COMPASS preliminary results for these six "beyond Collins and Sivers" asymmetries, obtained from transversely polarized deuteron and proton data have been presented at the previous conferences \cite{Parsamyan:2007ju} - \cite{Parsamyan:2013ug}. In this review we focus on the results obtained with the last "proton-2010" data sample.Comment: 6 pages, 12 figures, XXI International Workshop on Deep-Inelastic Scattering and Related Subject -DIS2013, 22-26 April 2013, Marseilles,Franc

Polarized Drell-Yan at COMPASS-II: Transverse Spin Physics Program

Successful realization of polarized Drell-Yan physics program is one of the main goals of the second stage of the COMPASS experiment. Drell-Yan measurements with high energy (190 GeV/c) pion beam and transversely polarized NH3 target have been initiated by a pilot-run in the October 2014 and will be followed by 140 days of data taking in 2015. In the past twelve years COMPASS experiment performed series of SIDIS measurements with high energy muon beam and transversely polarized deuteron and proton targets. Results obtained for Sivers effect and other target transverse spin dependent and unpolarized azimuthal asymmetries in SIDIS serve as an important input for general understanding of spin-structure of the nucleon and are being used in numerous theoretical and phenomenological studies being carried out in the field of transvers-spin physics. Measurement of the Sivers and all other azimuthal effects in polarized Drell-Yan at COMPASS will reveal another side of the spin-puzzle providing a link between SIDIS and Drell-Yan branches. This will be a unique possibility to test universality and key-features of transverse momentum dependent distribution functions (TMD PDFs) using essentially same experimental setup and exploring same kinematic domain. In this review man physics aspects of future COMPASS polarized Drell-Yan measurement of azimuthal transverse spin asymmetries will be presented, giving a particular emphasis on the link with very recent COMPASS results obtained for SIDIS transverse spin asymmetries from four "Drell-Yan" $Q^2$-ranges.Comment: 6 pages, 7 plots. SPIN-2014, Beijing, China. arXiv admin note: text overlap with arXiv:1411.156

Transverse spin azimuthal asymmetries in SIDIS at COMPASS: Multidimensional analysis

COMPASS is a high-energy physics experiment operating at the SPS at CERN. Wide physics program of the experiment comprises study of hadron structure and spectroscopy with high energy muon and hadrons beams. As for the muon-program, one of the important objectives of the COMPASS experiment is the exploration of the transverse spin structure of the nucleon via spin (in)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 $^{6}LiD$ (in 2002, 2003 and 2004) and $NH_{3}$ (in 2007 and 2010) targets. The experimental results obtained by COMPASS for unpolarized target azimuthal asymmetries, Sivers and Collins effects and other azimuthal observables play an important role in the general understanding of the three-dimensional nature of the nucleon. Giving access to the entire "twsit-2" set of transverse momentum dependent parton distribution functions and fragmentation functions COMPASS data triggers constant theoretical interest and is being widely used in phenomenological analyses and global data fits. In this review main focus is given to the very recent results obtained by the COMPASS collaboration from first ever multi-dimensional extraction of transverse spin asymmetries.Comment: 8 pages, 8 figures. SPIN-2014, Beijing, Chin

New target transverse spin dependent azimuthal asymmetries from COMPASS experiment

In general, eight target transverse spin-dependent azimuthal modulations are allowed in semi inclusive deep inelastic scattering of polarized leptons on a transversely polarized target. In the QCD parton model four of these asymmetries can be interpreted within the leading order approach. Two of them, namely Collins and Sivers effects were already measured by HERMES and COMPASS experiments. Other two leading twist and remaining four azimuthal asymmetries which can be interpreted as twist-three contributions have been measured for the first time in COMPASS using a 160 GeV/c longitudinally polarized ($P_{beam}\simeq -0.8$) muon beam and a transversely polarized $^6LiD$ target. We present here the preliminary results from the 2002-2004 data.Comment: 4 pages, 8 figures, talk delivered at conference: "SYMMETRIES AND SPIN (SPIN-Praha-2007)" Prague, July 8 - July 14, 200

Analysis and Interpretation of Transverse Spin Dependent Azimuthal Asymmetries in SIDIS at the COMPASS Experiment

In general, eight target transverse spin-dependent azimuthal modulations are allowed in semi-inclusive deep inelastic scattering (SIDIS) of polarized leptons on a transversely polarized target. In the QCD parton model four of these asymmetries can be interpreted within the leading order approach and other four are twist-three level contributions. Two leading twist transverse spin asymmetries, namely Collins and Sivers effects were already published by HERMES and COMPASS collaborations. While the remaining six new asymmetries have been measured for the first time in COMPASS using a high energy longitudinally polarized muon beam and a transversely polarized deuterium target. In the introductory chapter of this thesis we describe the general expression of the cross-section of polarized SIDIS and review the aspects of the QCD parton model with transverse momentum dependent distribution and fragmentation functions. Then we define the target transverse spin asymmetries arising in SIDIS and motivate the importance of their measurement. The two subsequent chapters are dedicated to our study of the double spin asymmetries ALT and ALL; calculations and the prediction plots for x,y,z and PhT dependence of asymmetries for COMPASS, HERMES and JLab experiments are presented. In chapters 5–7 we describe the COMPASS experimental setup, review the general aspects of the data analysis procedure (event selection, analysis methods, systematic st udies and cross-checks) and present the results on target transverse spin dependent azimuthal asymmetries extracted from COMPASS 2002-2004 data. Asymmetries are evaluated as a functions of x,y,z and PhT kinematic variables for positive and negative unidentified hadrons and for positive and negative pions and kaons. At the end of the thesis we summarize the obtained results and draw some conclusions

Transverse spin dependent azimuthal asymmetries at COMPASS

In semi-inclusive deep inelastic scattering of polarized leptons on a transversely polarized target eight target transverse spin-dependent azimuthal modulations are allowed. In the QCD parton model half of these asymmetries can be interpreted within the leading order approach and the other four are twist-three contributions. The first two leading twist asymmetries extracted by HERMES and COMPASS experiments are related: one to the transversity distribution and the Collins effect, the other to the Sivers distribution function. These results triggered a lot of interest in the past few years and allowed the first extractions of the transversity and the Sivers distribution functions of nucleon. The remaining six asymmetries were obtained by the COMPASS experiment using a 160 GeV/c longitudinally polarized muon beam and transversely polarized deuteron and proton targets. Here we review preliminary results from COMPASS proton data of 2007.Comment: 5 pages, 4 figures, Proceedings of SPIN2010 international symposium, J\"ulich, Germany, September 27 - October 2, 201

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

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. © 2015