Measurement of the gluon polarization $\Delta G/G$ at COMPASS

One of the key objectives of the COMPASS experiment at CERN is the determination of the gluon contribution to the nucleon spin. The gluon polarization is measured via photon-gluon fusion in deep-inelastic scattering of 160 GeV/c polarized muons on a polarized $^{6}$LiD solid-state target. Photon-gluon fusion is tagged by the observation of charmed mesons or the production of hadron pairs with large transverse momenta $p_{t}$. The status of the analysis of the $D^{0}$ and $D^{0*}$ events and of the high-$p_{t}$ hadron pairs is shown. The gluon polarization $\Delta G/G$ has been determined from the asymmetry of high-$p_{t}$ hadron pairs with $Q^{2} >$ 1 GeV/c$^{2}$ in an analysis of the 2002/03 data as $\Delta G/G =$ 0.06 $\pm$ 0.31($stat.$) $\pm$ 0.06($syst.$).