Sivers asymmetry extracted in SIDIS at the hard scales of the Drell–Yan process at COMPASS

Abstract

Eight proton transverse-spin-dependent azimuthal asymmetries are extracted in four regions of the photon virtuality Q2 from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon–nucleon scattering. These Q2 regions correspond to the four regions of the di-muon mass View the MathML source used in the ongoing analyses of the COMPASS Drell–Yan measurements, which allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. In addition, for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function various two-dimensional kinematic dependences are presented. The integrated Sivers asymmetries are found to be positive with an accuracy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics

Measurement of target-polarization dependent azimuthal asymmetries in SIDIS and Drell-Yan processes at COMPASS experiment

“…Hence it is not excluded that TMD evolution effects may be sizable when describing the STAR results using Sivers TMD PDFs extracted from fixed-target SIDIS results. In order to further test this conjecture and provide a valuable input for testing the effect of TMD evolution, COMPASS recently performed the first multi-differential analysis of the TSAs extracting them from SIDIS data at four different hard scales [36]. These Q 2 regions were chosen to match the four regions of the di-muon mass used in the ongoing analyses of the COMPASS Drell-Yan measurements, which allows for a direct comparison of the nucleon TMD PDFs extracted from these two alternative measurements.…”

Sivers asymmetry in the pion induced Drell-Yan process at COMPASS within transverse momentum dependent factorization

“…The general expression of the structure functionW UT is given in Eq. (8). The evolution functions for the Sivers function in the b-spacef ⊥αðDYÞ 1Tq=p…”

“…It can also give rise to the single-spin asymmetry in various high energy scattering processes. During the last decade, the Sivers asymmetry in semi-inclusive deep inelastic scattering (SIDIS) has been measured by the HERMES [3,4], COMPASS [5][6][7][8], and Jlab Hall A [9] Collaborations. The data from these experiments were utilized by several groups [10][11][12][13][14][15] to extract the quark Sivers functions of the proton.…”

“…The polarized Drell-Yan data from COMPASS, together with the previous measurement of the Sivers effect in the W-and Z-boson production from p ↑ p collision at relativistic heavy ion collider (RHIC) [30], provide the first evidence of the sign change of the Sivers function. The COMPASS experiment has the unique advantage to explore the sign change of the Sivers function since it has almost the same setup [8,25] for SIDIS and Drell-Yan process, which may reduce the uncertainties in the extraction of the Sivers function from the two kinds of measurements. An important issue in the comparison of observables between the SIDIS and Drell-Yan-type processes is that the typical energy scales for existing SIDIS facilities are quite different from those for the existing and planned hadron-hadron collision facilities.…”

Transversely polarized Drell-Yan measurements at COMPASS

“…This offers the opportunity of minimizing the uncertainties related to the TMD evolution in the comparison of the Sivers TMD PDFs when extracted from these two measurements to test the opposite-sign prediction by QCD. Recently, COMPASS published the first multi-differential results of the TSAs, which were extracted from SIDIS data at four different hard scales [9]. In order to simplify the comparison with the Drell-Yan case, one of the selected Q 2 ranges was chosen to be the same as the one selected for DY TSAs analysis.…”