Abstract
The transverse momentum ( $$p_{\mathrm T}$$ ) distribution of primary charged particles is measured at midrapidity in minimum-bias p–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}=5.02$$ TeV with the ALICE detector at the LHC in the range $$0.15<p_{\mathrm T}<50$$ GeV/ $$c$$ . The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for $$p_{\mathrm T}$$ larger than 2 GeV/ $$c$$ , with a weak indication of a Cronin-like enhancement for $$p_\mathrm {T}$$ around 4 $$\mathrm {GeV}\!/c$$ . The measurement is compared to theoretical calculations and to data in Pb–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}=2.76$$ TeV.
Highlights
Measurements of particle production in proton-nucleus collisions at high energies enable the study of fundamental properties of Quantum Chromodynamics (QCD) over a broad range of parton fractional momentum x and parton densities
The first measurements of charged-particle production in minimum-bias p–Pb collisions at the LH√C at a centre-ofmass energy per nucleon-nucleon pair of sNN = 5.02 TeV [3,4] showed that: (i) the charged particle multiplicity density at midrapidity scales approximately with the number of participating nucleons ( Npart = 7.9 ± 0.6 for minimumbias collisions) calculated in a Glauber model [5] and (ii) the transverse momentum spectrum, measured in the range 0.5–20 GeV/c [4], exhibits binary collision scaling above a few GeV/c, as expected in the absence of any significant nuclear modification effect. The latter is quantified by the nuclear modification factor, RpPb, the ratio of the pT spectrum in p–Pb collisions and a reference obtained by scaling the measurement in pp collisions with the number of binary nucleon-nucleon collisions in p–Pb
In this letter we present an update of our previously published pT spectra of primary charged particles [4] based on the 60 times larger sample size collected with the ALICE detector [8] in 2013 in minimum-bias collisions
Summary
The latter is quantified by the nuclear modification factor, RpPb, the ratio of the pT spectrum in p–Pb collisions and a reference obtained by scaling the measurement in pp collisions with the number of binary nucleon-nucleon collisions in p–Pb. The preliminary result by the CMS collaboration [6] hints at an enhancement e-mail: alice-publications@cern.ch of particle production in p–Pb collisions above binary collision scaling, leading to RpPb > 1, for pT exceeding about 30 GeV/c. The spectra are corrected on a statistical basis using the measurements by ALICE in p–Pb collisions of the η distribution of inclusive charged particle production [3] and of the pion, kaon, and proton yields [12]; this correction depends on the ηcms range and on pT, reaching about 20 % for the lowest pT bin.
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