Two-dimensional fitting procedure to extract asymmetries in SIDIS at COMPASS

COMPASS, a fixed target experiment on the SPS M2 beamline at CERN, has started to collect physics data from Autumn 2001 on a polarized 6LiD target. This target can be both longitudinally and transversely polarized with respect to the polarized 160 GeV/c μ+ beam. In 2002, 2003 and 2004, 20% of the beam-time was spent in the transverse configuration, allowing the measurement of transverse spin effects, predicted to give rise to numerous asymmetries in semi-inclusive DIS, related to the azimuthal angles of the target spin(φs) and the produced hadron(φh). To extract the full set of asymmetries simultaneously and to study the correlation between any chosen pair, two-dimensional fitting procedure was implemented. This method will be described and results will be presented for the Collins (AUTsin(φh+φs-π)) and Sivers (AUTsin(φh-φs)) asymmetries which were already published from one-dimensional fitting procedure, as well as other moments e.g azimuthal double spin asymmetry (ALTcos(φh-φs)). The ALT asymmetry arises due to the longitudinal polarization of quarks in the transversely polarized nucleon. The corresponding distribution function g1T(x, kT2) can be related to the ordinary helicity distribution function g1(x) measured in DIS. (orig.)