Transverse momentum distributions of charged particles in pp and nuclear collisions with ALICE at the LHC

Abstract

The charged-particle transverse momentum spectrum in pp collisions is an important observable for testing perturbative QCD calculations and serves as a reference for heavy-ion collisions to study the properties of deconfined matter created in nucleus-nucleus (AA) collisions. The study of inclusive charged particle spectra gives information on parton energy loss in the medium created in AA collisions, leading to a suppression of hadron production at high transverse momentum ($p_{\rm T}$). This effect can be investigated by calculating the nuclear modification factor, defined as the ratio between the $p_{\rm T}$ spectrum measured in nucleus-nucleus collisions and a reference spectrum in pp collisions scaled by the number of binary collisions. ALICE has measured pp collisions over a large energy range $\sqrt{\textrm{s}} = $13, 7, 5.02 and 2.76 TeV, p-Pb at $\sqrt{\textrm{s}_{\rm NN}} = $5.02 TeV, Xe-Xe at $\sqrt{\textrm{s}_{\rm NN}} = $5.44 TeV and Pb-Pb $\sqrt{\textrm{s}_{\rm NN}} = $5.02 TeV and 2.76 TeV. We show the $p_{\rm T}$ spectra in pp and nuclear collisions as well as the nuclear modification factors with an exceptional precision as compared to previous results.