31 research outputs found
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--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 -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--z-pT multidimensional results for
transverse spin asymmetries recently obtained by COMPASS will serve as a direct
and unprecedented input for TMD -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
(in 2002, 2003 and 2004) and (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" -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 (in 2002, 2003 and 2004) and
(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
() muon beam and a transversely polarized 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