Recent COMPASS results on the gluon polarization

The spin structure of the nucleon is studied in the COMPASS experiment at CERN/SPS, from the collisions of 160 GeV polarized muon beam with a $^{6}$LiD target. The data collected from 2002 to 2006 provide an accurate measurement of longitudinal double spin cross-section asymmetries. The latest results on the gluon polarization, accessed from two independent analyses of photon-gluon fusion selected events, are presented. The study of the open-charm production allows to extract the gluon polarization (in LO QCD) from the measurement of the asymmetry, the value obtained being $\Delta g/g = -$ 0.49 $\pm$ 0.27($stat$) $\pm$ 0.11($syst$), at an average $x_{g} =$ 0.11$^{+0.11}_{-0.05}$ and a scale $\langle\mu^{2}\rangle =$ 13 (GeV/c)$^{2}$. An alternative and independent way to study the gluon polarization, by studying the high transverse momentum hadron pairs produced, leads to a value $\Delta g/g =$ 0.08 $\pm$ 0.10($stat$) $\pm$ 0.05($syst$), at $x^{av}_{g} =$ 0.082$^{+0.041}_{-0.027}$ and $\langle\mu^{2}\rangle =$ 3 (GeV/c)$^{2}$.