New measurement of $\Delta G/G$ at COMPASS from open charm events

The gluon polarization, $\Delta g/g$, in the nucleon was measured using COMPASS data taken between 2002 and 2006. The analysis relies on the search for open-charm events with the production of $D$-mesons in order to isolate photon-gluon fusion processes. This method is characterized by the absence of physical backgrounds, oering a very clean extraction of $\Delta g/g$. It is however statistically limited, that is why a weighted method was developed to minimize the statistical error. The preliminary result is : $\langle\frac{\Delta g}{g}\rangle= -$0.49 $\pm$ 0.27 $\pm$ 0.11(syst.).