Charged particle multiplicity studies in proton-proton collisions at a centre-of-mass energy of 10 TeV with the ALICE detector

Particle multiplicity is one of the basic observables in hadron and nuclear collisions. In a proton-proton (pp) system, the measured multiplicity distributions indicate that the hadrons emerging from the collision cannot be considered as produced independently from each other. Furthermore, the correlation between the forward and backward multiplicities reveals the longitudinal size of the particle sources. Sound understanding of these effects in pp system is prerequisite before a similar study of nuclear collisions can be undertaken. In this work I describe a charged particle multiplicity analysis prepared for the ALICE experiment at CERN LHC. The analysis is focused on multiplicity distributions and forward-backward multiplicity correlations, and was extensively tested using simulated pp collision events. The latter were produced using realistic event generators tuned for the energies at which experimental data exist, and extrapolated to LHC. The analysis scheme and the results are described in Sections 4 and 5. The emphasis is put on the response of the ALICE apparatus to the observables under discussion. The multiplicity analysis is based on the particle tracks measured with the ALICE Time Projection Chamber (TPC). The TPC is an excellent charged particle detector with large coverage and high resolution, the latter, however, achievable only if the working conditions are well under control. Two essential parameters, the electron drift velocity and the gas gain, are monitored by a dedicated device called Gas prOportional cOunter For drIfting Electrons (GOOFIE). Installation, commissioning, and operation of GOOFIE, described in Section 2.3, were the practical part of this thesis work