Charm production and fragmentation fractions at midrapidity in pp collisions at s = 13 TeV

Abstract

Measurements of the production cross sections of prompt $D^{0}$, $D^{+}$, $D^{*+}$, $D_{s}^{+}$, $\Lambda_{c}^{+}$, and $\Xi_{c}^{+}$ charm hadrons at midrapidity in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ALICE detector are presented. The D-meson cross sections as a function of transverse momentum ($p_{T}$) are provided with improved precision and granularity. The ratios of $p_{T}$-differential meson production cross sections based on this publication and on measurements at different rapidity and collision energy provide a constraint on gluon parton distribution functions at low values of Bjorken-x ($10^{-5}$–$10^{-4}$). The measurements of $\Lambda_{c}^{+}$ ($\Xi_{c}^{+}$) baryon production extend the measured $p_{T}$ intervals down to $p_{T} = 0(3)$ GeV/c. These measurements are used to determine the charm-quark fragmentation fractions and the $c\bar{c}$ production cross section at midrapidity ($|y| < 0.5$) based on the sum of the cross sections of the weakly-decaying ground-state charm hadrons $D^{0}$, $D^{+}$, $D_{s}^{+}$, $\Lambda_{c}^{+}$, $\Xi_{c}^{0}$ and, for the first time, $\Xi_{c}^{+}$, and of the strongly-decaying $J/\psi$ mesons. The first measurements of $\Xi_{c}^{+}$ and $\Sigma_{c}^{0,++}$ fragmentation fractions at midrapidity are also reported. A significantly larger fraction of charm quarks hadronising to baryons is found compared to $e^{+}e^{-}$ and $ep$ collisions. The $c\bar{c}$ production cross section at midrapidity is found to be at the upper bound of state-of-the-art perturbative QCD calculations.