Measurements at COMPASS of transverse spin effects on identified hadrons on a transversely polarised proton targeta

The Semi-Inclusive Deep Inelastic Scattering (SIDIS) cross section, that describes the scattering of a charged lepton (+) o a nucleon (proton) transversely polarised with respect to its momentum, and with the detection of a hadron in the nal state ( l p" ! l0 h X), has 8 independent azimuthal modulations, that depends on the spin of the target nucleon and on the lepton momentum. Among these modulations, the most famous are due to the Collins and Sivers eects. The Collins eect is the asymmetric fragmentation of a polarised quark into a hadron, and the amplitude of the modulation is proportional to the Collins fragmentation function with the transversity parton distribution function, that gives the probability dierence to nd a quark with the polarisation parallel or anti-parallel to the nucleon spin in a transversely polarised nucleon. The Sivers eect is due to the coupling of the quark transverse momentum and the spin in a transversely polarised nucleon. The other six modulations are due to other correlations between the quark polarisation or the quark transverse momentum and the nucleon spin. The work presented in this Thesis is the measurement of the amplitude of the azimuthal modulations (asymmetries) on the data of the COMPASS experiment, collected in 2007 using a NH3 target to access the polarised proton, focusing on the Collins and Sivers asymmetries. The asymmetries have been measured both the charged hadrons and on hadrons identied making use of the ring-imaging Cherenkov detector RICH-1 . Large part of the work presented here is devoted to the determination of the systematic error of the measurement.