Eur. Phys. J. A (2007) 31: 620-625
https://doi.org/10.1140/epja/i2006-10251-1

QNP 2006

Spin physics at COMPASS

Physik Department, Technische Universität München, Germany

Received: 23 November 2006
Accepted: 30 November 2006
Published online: 15 March 2007

Abstract

Results for the spin structure of the nucleon from the COMPASS data taking periods 2002 to 2004 are presented. The quark contribution to the nucleon spin, following from a QCD fit to the new data, turns out to be significantly larger than it was derived from the previous world data. The new data favour, on the other side, a comparatively small gluon polarisation in the range x _g ≈ 0.1. In the data taken with the deuteron target polarised transversely the related asymmetries are found to be small on the level of accuracy reached so far, indicating a cancellation of the proton and neutron contributions. This is in agreement, for both the Collins and the Sivers asymmetry, with recent theoretical calculations. Also, a step towards the understanding of angular-momentum contributions with COMPASS is taken by the evaluation of asymmetries in exclusive vector meson production.