Charm Production and Fragmentation Fractions at Midrapidity in pp Collisions at s = 13 TeV

Measurements of the production cross sections of prompt D0, D+, D*+, Ds+, Λc+, and Ξc+ charm hadrons at midrapidity in proton-proton collisions at s = 13 TeV with the ALICE detector are presented. The D-meson cross sections as a function of transverse momentum (pT) are provided with improved precision and granularity. The ratios of pT-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 Λc+ (Ξc+) baryon production extend the measured pT intervals down to pT = 0(3) GeV/c. These measurements are used to determine the charm-quark fragmentation fractions and the cc¯ production cross section at midrapidity (|y| < 0.5) based on the sum of the cross sections of the weakly-decaying ground-state charm hadrons D0, D+, Ds+, Λc+, Ξc0 and, for the first time, Ξc+, and of the strongly-decaying J/ψ mesons. The first measurements of Ξc+ and Σc0,++ 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 cc¯ production cross section at midrapidity is found to be at the upper bound of state-of-the-art perturbative QCD calculations.