Charm fragmentation fractions and $\mathrm{c}\overline{\mathrm{c}}$ cross section in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

Abstract

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

21 pages, 2 captioned figures, 2 tables, authors from page 15, published version, figures at http://alice-publications.web.cern.ch/node/10966

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