Measurement of the Gluon Polarization $Δg/g$ from Open Charm at COMPASS

We have measured the gluon polarization in the nucleon by detecting charm production via $D0$ meson decay to charged K and π in polarized muon scattering off a longitudinally polarized deuteron target. The dominant process for charm production is the photon gluon fusion into a charm anti‐charm quark pair. By using all deuteron statistics from COMPASS accumulated between 2002 and 2006, we extract double spin asymmetries in bins of the transverse momentum and the energy of the $D0$ meson and we perform a leading order analysis of the data to extract the gluon polarization $〈Δg/g〉 = −0.49±0.27(stat)±0.11(syst)$ at a Quantum Chromodynamics (QCD) scale $μ2 = 13 GeV2$ and at a gluon momentum fraction $〈x〉 = 0.11.$