Transverse Spin Physics at COMPASS

TL;DR

The paper reports on COMPASS's measurements of transverse spin effects in deep inelastic scattering, finding small asymmetries consistent with quark flavor cancellations, and discusses future data collection on polarized proton targets for additional insights.

Contribution

It presents the first measurements of transversity PDFs at COMPASS using multiple quark polarimeters and discusses upcoming experiments with polarized proton targets.

Findings

All measured asymmetries are small and compatible with zero.

Results suggest a cancellation between u and d-quark contributions.

Future data from polarized proton targets will provide complementary information.

Abstract

The study of transverse spin effects is part of the scientific program of COMPASS, a fixed target experiment at the CERN SPS. COMPASS investigates the transversity PDFs in semi-inclusive DIS, using a longitudinally polarized muon beam of 160 GeV/c impinging on a transversely polarized target. From 2002 to 2004, data have been collected using a $^6$LiD target transversely polarized. Transversity has been measured using different quark polarimeters: the azimuthal distribution of single hadrons, the azimuthal dependence of the plane containing hadron pairs, and the measurement of the transverse polarization of baryons ($\Lambda$ hyperons). All the asymmetries have been found to be small, and compatible with zero, a result which has been interpreted as a cancellation between the u and d-quark contributions. In 2007 COMPASS has taken data using a NH$_3$ polarized proton target which will give complementary information on transverse spin effects.