New measurements of transverse spin asymmetries at COMPASS

The study of transverse momentum effects and transverse spin structure of the nucleon is an important part of the scientific program of COMPASS, a fixed target experiment at the CERN SPS. The transverse effects are investigated via semi inclusive DIS reactions with a 160 GeV /c muon beam impinging on transversely polarised targets. The hadrons produced in the reactions are detected in a wide momentum and angular range by a two-stage spectrometer. A deuterium target has been used in the first part of COMPASS data taking from 2002 to 2004, while a proton target has been used in 2007 and 2010. Here we present the recent results obtained from the 2010 data on different channels, involving the azimuthal distribution of single hadrons and the azimuthal dependence of the plane cont aining hadron pairs. The results confirm the published results of the 2007 data taking with an improved statistical significance; the measured azimuthal asymmetries are clearly non zero, at variance with those measured on a deuterium target.