Charm fragmentation fractions and cc¯ cross section in p–Pb collisions at √ˢɴɴ=5.02TeV

Abstract

The total charm-quark production cross section per unit of rapidity dσ (cc̄)/dy, and the fragmentation fractions of charm quarks to different charm-hadron species f (c → hc), are measured for the first time in p—Pb collisions at √ˢɴɴ = 5.02 TeV at midrapidity (−0.96 < y < 0.04 in the centre-of-mass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measure-ments of prompt production of ground-state charm-hadron species: D⁰, D⁺, Dₛ⁺, and J/ψ mesons, and Λ⁺c and ⁰c baryons. The resulting cross section is dσ (cc̄)/d y = 219.6 ± 6.3 (stat.) ₋₁₁.₈⁺¹⁰·⁵ (syst.) ⁺⁸·³₋₂.₉ (extr.) ± 5.4 (BR) ± 4.6 (lumi.) ± 19.5 (rapidity shape) +15.0 (Ω⁰c ) mb, which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are com- patible with those measured in pp collisions at √s = 5.02 and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p—Pb collisions compared with e⁺e⁻ and e⁻ p collisions. The pT-integrated nuclear modification factor of charm quarks, RpPb(cc̄) = 0.91 ± 0.04 (stat.) ⁺⁰·⁰⁸₋₀.₉ (syst.) ⁺⁰·⁰⁵₋₀.₀₃ (extr.) ± 0.03 (lumi.), is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions.