Analysis of charged particle production in proton-nucleus and proton-proton collisions at the LHCb experiment

This thesis presents the measurement of prompt charged particle production in proton-lead and proton-proton collisions at the centre-of-mass energy of $\sqrt{s_{\mathrm{NN} } }=5.02\,\mathrm{TeV}$ in the LHCb experiment at CERN. Double-differential cross-sections of prompt charged particles are determined in the two systems as a function of pseudorapidity ($\eta$) and transverse momentum ($p_\mathrm{T}$) with respect to the proton beam. With the measured cross-sections, the nuclear modification factor $R_{pPb}$ for charged particles is determined covering an acceptance of $-4.8<\eta<-2.5$ (backward region) and $2.0<\eta<4.8$ (forward region), and $0.2 < p_\mathrm{T}<8.0\,\mathrm{GeV}/c$. The results show a suppression of charged particle production in proton-lead collisions relative to proton-proton collisions in the forward region and an enhancement in the backward region for $p_\mathrm{T}$ larger than $1.5\,\mathrm{GeV}/c$. This measurement constrains nuclear PDFs and saturation models at previously unexplored values of the parton fractional momentum down to $10^{-6}$.