Study of global observables in p-p and A-A collisions with ALICE at LHC

This thesis deals with the reconstruction of charged particles using the information provided by the ALICE Silicon Pixel Detector. The algorithm to reconstruct particles crossing the SPD in p-p and Pb-Pb interactions has been thoroughly studied: the association strategy has been modified and the cut optimized to improve its performance. An analysis method to correct the pseudorapidity density distribution and a method to estimate the charged multiplicity event-by-event have been developed. Some of the systematic errors associated to the pseudorapidity density measurement have been estimated. The analysis has been applied to the first p-p data at the LHC, collected in November 2010.