Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pT.

We measured the longitudinal double spin asymmetries A LL for single hadron muoproduction off protons and deuterons at photon virtuality Q 2 < 1 ( GeV / c ) 2 for transverse hadron momenta p T in the range 1 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 LiD or NH 3 targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation Δ G inside the nucleon in the range of the nucleon momentum fraction carried by gluons 0.05 < x g < 0.2 . [ABSTRACT FROM AUTHOR]