Recent measurement of $\Delta G/G$ at COMPASS

We present a preliminary measurement of the gluon polarization $\Delta G/G$ in the nucleon, based on the spin asymmetry of quasi-real photoproduction events for which a pair of large transverse momentum hadrons is produced. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a large polarized $^{6}$LiD target. The preliminary helicity asymmetry for the selected events is $A_{\|}/D =$ 0.002 $\pm$ 0.019(stat.) $\pm$ 0.003 (exp.syst.). From this value, a leading order analysis based on the model of PYTHIA leads to the gluon polarization in the nucleon $\Delta G/G(x_{g} =$ 0.095, $\mu^{2} =$ 3 GeV$^{2}) =$ 0.024 $\pm$ 0.089(stat.) $\pm$ 0.057(syst.). This value is consistent with parameterizations obtained from QCD fits to the $g_{1}$ data, with a first moment $\Delta G \equiv \int^{1}_{0}\Delta G(x)dx \simeq$ 0.5, at the same scale.