Measurements of particle production and particle correlations in proton-proton and proton-ion collisions with LHCb

Abstract

In this thesis, measurements of particle production and particle correlations using proton-proton (pp) and proton-ion (pPb) collisions recorded with the LHCb experiment at the Large Hadron Collider are presented. The charged particle multiplicity and the differential charged particle density are studied in pp collisions at a centre-of-mass energy of sqrt{s}=7TeV. The measurement is performed for events with at least one charged particle in the kinematic range of p>2 GeV/c, pT>0.2 GeV/c and 2.0<Eta<4.8. The mean particle multiplicity, mu, and the corresponding root-mean-square deviation, sigma, are measured to be mu=11.30+-0.01+-0.09 and sigma=9.50+-0.01+-0.02, where the uncertainties are statistical and systematic, respectively. Results for particle multiplicities and particle densities are presented as functions of Eta and pT of the particles, and are compared to predictions from different Monte Carlo event generators. Furthermore, a measurement of two-particle angular correlations is performed by using charged particles produced in pPb collisions at a nucleon-nucleon centre-of-mass energy of sqrt{s_NN}=5.02TeV. Data with two different beam configurations are analysed, in which either the proton or the nucleus remnant is traversing the LHCb detector. The particle correlations are measured using the azimuthal angle separation, dEta, and pseudorapidity separation, dPhi. The emergence of a correlation structure on the near side (dPhi=0), elongated over a long range in dEta is observed for particles in a pT-range of 1-3 GeV/c in events exhibiting a high particle multiplicity. This measurement is the first observation of the near-side ridge in pPb collisions in the forward region and complements similar observations in pp and pPb collisions in the central rapidity region.