Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$

Abstract

We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$c$)${}^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$c$ to 4 GeV/$c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$c$ or 200 GeV/$c$ impinging on polarised ${}^6\mathrm{LiD}$ or $\mathrm{N}{\mathrm{H}}_3$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\hat{I}”G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05<x_g<0.2$.