Spin asymmetries for events with highpThadrons in DIS and an evaluation of the gluon polarization

Abstract

We present a measurement of the longitudinal spin cross section asymmetry for deep-inelastic muon-nucleon interactions with two high transverse momentum hadrons in the final state. Two methods of event classification are used to increase the contribution of the photon-gluon fusion process to above 30%. The most effective one, based on a neural network approach, provides the asymmetries $A_p^{\mathcal{l}\overrightarrow{N}\mathcal{l}\mathrm{hhX}}=0.030\mathrm{}\pm 0.057\left(\mathrm{stat}\right)\pm 0.010\left(\mathrm{syst}\right)$ and $A_d^{\mathcal{l}\overrightarrow{N}\mathcal{l}\mathrm{hhX}}=0.070\mathrm{}\pm 0.076\left(\mathrm{stat}\right)\pm 0.010\left(\mathrm{syst}\right).\mathrm{}$ From these values we derive an averaged gluon polarization $\Delta G/G=-0.20\pm 0.28\left(\mathrm{stat}\right)\pm 0.10\left(\mathrm{syst}\right)$ at an average fraction of nucleon momentum carried by gluons $〈\eta 〉=\mathrm{0.07.}\mathrm{}$