Measurement of the Collins and Sivers asymmetries on transversely polarised protons

TL;DR

This paper reports measurements of Collins and Sivers asymmetries in deep inelastic scattering on transversely polarized protons, providing experimental data that supports current theoretical models of quark distributions and fragmentation functions.

Contribution

First measurement of Collins and Sivers asymmetries on transversely polarized protons at CERN, confirming theoretical predictions with new experimental data.

Findings

Non-zero Collins asymmetries at large Bjorken x for both hadron charges.

Sivers asymmetry for positive hadrons is slightly positive across x range.

Results support leading-twist quark distribution and fragmentation function models.

Abstract

The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results nicely support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fragmentation functions.