Study of Low Mass Dimuon Production in 400 GeV Proton-Nucleus Collisions at the CERN-SPS with the NA60 Apparatus

This thesis reports on the data collected at the CERN SPS in p-A collisions at 400 GeV, with the NA60 apparatus, during the 2004 proton run. NA60 is a fixed target experiment at the CERN SPS accelerator, studying both proton-nucleus and nucleus-nucleus collisions in the dimuonic channel. Data were taken between 2002 and 2004, and the analyses are currently still in progress. The present work focuses on the analysis of the data collected by NA60 during three days within the 2004 run, in collisions between 400 GeV protons and targets of seven different nuclear species. The selection of the data is presented, which allowed to define the final sample of events to be analyzed. Then the transverse momentum spectrum of the phi meson is studied, for each proton-nucleus system. Finally, the average value of the phi's transverse momentum is extracted and studied as a function of the mass number A of the target. The analysis allowed to observe a rising trend of the average transverse momentum of the phi as a function of A, which could be explained in terms of the so-called "Cronin Effect".