Measurements of Collins and Sivers asymmetries at COMPASS

TL;DR

This paper reports measurements of Collins and Sivers asymmetries in semi-inclusive deep inelastic scattering at COMPASS, providing insights into the spin structure of the nucleon from polarized muon-proton interactions.

Contribution

First measurements of Collins and Sivers asymmetries at COMPASS using transversely polarized targets with preliminary results presented.

Findings

Preliminary Collins asymmetry results indicate non-zero effects.

Sivers asymmetry measurements suggest significant transverse momentum distributions.

Data collected from 2002 provide new constraints on nucleon spin models.

Abstract

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 results are presented here.