Transverse spin effects in COMPASS

TL;DR

The paper reports on measurements of transverse spin effects in semi-inclusive deep inelastic scattering using the COMPASS experiment, focusing on Collins and Sivers asymmetries in proton targets.

Contribution

It presents new experimental results on transverse spin asymmetries in proton targets, expanding previous deuteron measurements and utilizing data from 2007 with NH_3 targets.

Findings

Observation of non-zero Collins asymmetries.

Observation of non-zero Sivers asymmetries.

Comparison with theoretical models.

Abstract

In the years 2002-2004 COMPASS has collected data with the LiD target polarization oriented transversely with respect to the muon beam direction for about 20% of the running time, to measure transverse spin effects in semi-inclusive deep inelastic scattering, one of the main objectives of the COMPASS spin program. In 2007, COMPASS has used for the first time a proton NH_3 target with the data taking time equally shared between longitudinal and transverse polarization of the target. After reviewing the results obtained with the deuteron, the new results for the Collins and Sivers asymmetries of the proton will be presented.