Transverse spin dependent azimuthal asymmetries at COMPASS

TL;DR

This paper reviews preliminary results from the COMPASS experiment on transverse spin-dependent azimuthal asymmetries in semi-inclusive deep inelastic scattering, providing insights into nucleon spin structure and related distribution functions.

Contribution

It presents the first measurements of six additional azimuthal asymmetries using polarized targets, expanding understanding of nucleon spin phenomena beyond previous leading twist results.

Findings

Observation of six new azimuthal asymmetries

Data supports models of transversity and Sivers functions

Enhanced understanding of twist-three contributions

Abstract

In semi-inclusive deep inelastic scattering of polarized leptons on a transversely polarized target eight target transverse spin-dependent azimuthal modulations are allowed. In the QCD parton model half of these asymmetries can be interpreted within the leading order approach and the other four are twist-three contributions. The first two leading twist asymmetries extracted by HERMES and COMPASS experiments are related: one to the transversity distribution and the Collins effect, the other to the Sivers distribution function. These results triggered a lot of interest in the past few years and allowed the first extractions of the transversity and the Sivers distribution functions of nucleon. The remaining six asymmetries were obtained by the COMPASS experiment using a 160 GeV/c longitudinally polarized muon beam and transversely polarized deuteron and proton targets. Here we review preliminary results from COMPASS proton data of 2007.