Direct estimate of the gluon polarization in the nucleon.

Abstract

We make a first crude direct estimate of the net gluon polarization in the proton, G, combining data on the asymmetries in high-pT hadron production from the HERMES, SMC and COMPASS collaborations. Although these data sample a restricted range of x, they provide no hint that G is large. Fixing the normalizations of different theoretical parametrizations using the hadron asymmetry data, we find typical central values of G ∼ 0.5, with uncertainties of similar magnitude. Values of G ≥ 2 are disfavoured by 2 ∼ 9 to 20, depending on the parametrization used.