Measurement of transverse spin effects in compass.

The argument of the thesis is the transverse spin physics, and the work done is in the framework of the COMPASS experiment, a fixed target experiment at the CERN SPS. COMPASS investigation of the nucleon spin structure is made by means of Deep Inelastic Scattering (DIS), obtained using a muon beam of 160 GeV/c scattering off a polarized deuterium target. In order to study the transverse spin effects, the target nucleons are polarized transversally with respect to the beam direction. The data collected by COMPASS with this target configuration in the years 2003-2004 have been analyzed in order to extract transverse spin asymmetries yielding information about the nucleon spin structure. In the data the DIS events with at least one hadron in the final state have been selected. The hadrons have been identified as pions or kaons using the RICH detector of the spectometer, and to this end a work of calibration of the detector has been performed. The main result of the analysis is the measurement of the Collins and the Sivers asymmetries on identified hadrons, for the first time measured on a deuterium target. The Sivers asymmetries bring information about the Sivers parton distribution function, describing the distribution of the transverse momentum of the quark inside a transversally polarized nucleon. Collins asymmetries are related to the transversity distribution function of the nucleon, giving the probability of finding a quark with the spin parallel or antiparallel to the nucleon spin, and on the Collins fragmentation function, describing the spin dependent part of the fragmentation process. The Sivers, Collins and transversity functions are not known, and their knowledge is of big importance in order to understand the nucleon spin structure. These functions have been extracted fitting the Collins and Sivers asymmetries measured in this thesis together with asymmetries from other experiments: the Collins and Sivers asymmetries measured from the HERMES experiment on a proton target, and the azimuthal asymmetries in hadron pair production in electron-positron annhihilation measured by the Belle Collaboration. As a result of the fit, the unknown functions for different quark flavor, in particular for the u and d valence quark, have been obtained. In the fit, different parametrizations for the unknown functions have been used, and the role of the asymmetries measured in this thesis has been studied. Due to the fact that both HERMES and Belle in the first part of 2007 have provided new set of measured asymmetries with respect to those analyzed in the existing works, the compatibility between the different set of data has also been studied.