Charm fragmentation fractions and \(\mathbf {c\overline{c}}\) cross section in p–Pb collisions at \(\mathbf {\sqrt{s _{NN}}=5.02 TeV}\)

Abstract

The total charm-quark production cross section per unit of rapidity \(\textrm{d}\sigma ({{\textrm{c}}\overline{\textrm{c}}})/\textrm{d}y\), and the fragmentation fractions of charm quarks to different charm-hadron species \(f(\textrm{c}\rightarrow {\textrm{h}}_{\textrm{c}})\), are measured for the first time in p–Pb collisions at \(\sqrt{s_\textrm{NN}} = 5.02~\text {Te}\hspace{-1.00006pt}\textrm{V} \) 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 measurements of prompt production of ground-state charm-hadron species: \(\textrm{D}^{0}\), \(\textrm{D}^{+}\), \(\textrm{D}_\textrm{s}^{+}\), and \(\mathrm {J/\psi }\) mesons, and \(\Lambda _\textrm{c}^{+}\) and \(\Xi _\textrm{c}^{0}\) baryons. The resulting cross section is \( \textrm{d}\sigma ({{\textrm{c}}\overline{\textrm{c}}})/\textrm{d}y =219.6 \pm 6.3\;(\mathrm {stat.}) {\;}_{-11.8}^{+10.5}\;(\mathrm {syst.}) {\;}_{-2.9}^{+8.3}\;(\mathrm {extr.})\pm 5.4\;(\textrm{BR})\pm 4.6\;(\mathrm {lumi.}) \pm 19.5\;(\text {rapidity shape})+15.0\;(\Omega _\textrm{c}^{0})\;\textrm{mb} \), which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at \(\sqrt{s} = 5.02\) 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 \(\mathrm {e^{+}e^{-}}\) and \(\mathrm {e^{-}p}\) collisions. The \(p_\textrm{T}\)-integrated nuclear modification factor of charm quarks, \(R_\textrm{pPb}({\textrm{c}}\overline{\textrm{c}})= 0.91 \pm 0.04\;\mathrm{(stat.)} ^{+0.08}_{-0.09}\;\mathrm{(syst.)} ^{+0.05}_{-0.03}\;\mathrm{(extr.)} \pm 0.03\;\mathrm{(lumi.)}\), is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions.