Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Collins asymmetries

TL;DR

This paper reports high-precision measurements of Collins asymmetries in muon-proton SIDIS processes, confirming previous findings and providing detailed insights into the transversity distributions of quarks within the proton.

Contribution

The study provides new, more accurate measurements of Collins asymmetries across a broad kinematic range, supporting models of quark transversity and the leading-twist nature of the asymmetry.

Findings

Confirmed previous Collins asymmetry measurements with higher accuracy.

Observed asymmetries for positive and negative hadrons are similar in magnitude and opposite in sign.

Data supports models where u-quark transversity is opposite in sign and larger than d-quark transversity.

Abstract

The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV positive muon beam and a transversely polarised NH_3 target. The Collins asymmetry of the proton was extracted in the Bjorken x range 0.003<x<0.7. These new measurements confirm with higher accuracy previous measurements from the COMPASS and HERMES collaborations, which exhibit a definite effect in the valence quark region. The asymmetries for negative and positive hadrons are similar in magnitude and opposite in sign. They are compatible with model calculations in which the u-quark transversity is opposite in sign and somewhat larger than the d-quark transversity distribution function. The asymmetry is extracted as a function of Bjorken $x$, the relative hadron energy $z$ and the hadron transverse momentum p_T^h. The high statistics and quality of the data also allow for more detailed investigations of the dependence on the kinematic variables. These studies confirm the leading-twist nature of the Collins asymmetry.