The Polarised Valence Quark Distribution from semi-inclusive DIS

TL;DR

This paper reports on measurements of the polarised valence quark distribution using semi-inclusive DIS data from the COMPASS experiment, providing insights into the asymmetry of light quark polarisation.

Contribution

It presents the first evaluation of the first moment of valence quark polarisation from semi-inclusive asymmetries, suggesting non-symmetric light quark polarisation.

Findings

Valence quark polarisation first moment = 0.40 ± 0.07 (stat.) ± 0.05 (syst.)

Supports non-symmetric polarisation of light antiquarks at two sigma confidence

Provides new data on valence quark distributions over a broad x range

Abstract

The semi-inclusive difference asymmetry A^{h^{+}-h^{-}} for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised ^6LiD target and cover the range 0.006 < x < 0.7 and 1 < Q^2 < 100 (GeV/c)^2. In leading order QCD (LO) the asymmetry A_d^{h^{+}-h^{-}} measures the valence quark polarisation and provides an evaluation of the first moment of Delta u_v + Delta d_v which is found to be equal to 0.40 +- 0.07 (stat.) +- 0.05 (syst.) over the measured range of x at Q^2 = 10 (GeV/c)^2. When combined with the first moment of g_1^d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Delta u-bar = - Delta d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Delta u-bar = Delta d-bar = Delta s-bar = Delta s.