Unpolarized Azimuthal Asymmetries from the COMPASS Experiment at CERN

2009 ◽  
Author(s):  
Rainer Joosten ◽  
Marvin L. Marshak ◽  
Keyword(s):  
Compass Experiment ◽  
Azimuthal Asymmetries

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

2016 ◽  
Vol 40 ◽  
pp. 1660109
Author(s):  
Bakur Parsamyan
Keyword(s):  
High Energy ◽  
Muon Beam ◽  
Distribution Functions ◽  
Transverse Spin ◽  
Spin Physics ◽  
Transverse Momentum Dependent ◽  
Spin Asymmetries ◽  
Compass Experiment ◽  
Physics Program ◽  
Azimuthal Asymmetries

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 main 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” [Formula: see text]-ranges.

Analytic study of azimuthal asymmetries in relativistic hollow e-beams

1980 ◽  
Vol 23 (8) ◽  
pp. 1596 ◽  
Author(s):  
B. G. Epstein ◽  
J. W. Poukey
Keyword(s):  
Analytic Study ◽  
Azimuthal Asymmetries

Color Entanglement in Hadronic Processes for Transverse Momentum Dependent Parton Distribution Functions

2015 ◽  
Vol 37 ◽  
pp. 1560022
Author(s):  
M. G. A. Buffing ◽  
P. J. Mulders
Keyword(s):  
Transverse Momentum ◽  
Parton Distribution ◽  
Distribution Functions ◽  
Parton Distribution Functions ◽  
Initial State ◽  
Color Flow ◽  
Transverse Momentum Dependent ◽  
Gauge Link ◽  
Azimuthal Asymmetries ◽  
Different Parts

In the description of protons, we go beyond the ordinary collinear parton distribution functions (PDFs), by including transverse momentum dependent PDFs (TMDs). As such, we become sensitive to polarization modes of the partons and protons that one cannot probe without accounting for transverse momenta of partons, in particular when looking at azimuthal asymmetries. Hadronic processes require the inclusion of gluon contributions forming the gauge links, which are path-ordered exponentials tracing the color flow. In processes with two hadrons in the initial state, such as Drell-Yan (DY), the gauge links from different parts of the process get entangled. We show that in color disentangling this gauge link structure, one becomes sensitive to this color flow. After disentanglement, particular combinations of TMDs will require a different numerical color factor than one naively might have expected. Such color factors will even play a role for azimuthal asymmetries in the simplest hadronic processes such as DY.

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