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^*+, D_s⁺, Λ_c⁺, and Ξ_c⁺ 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 (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 Λ_c⁺ (Ξ_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 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⁺, D_s⁺, Λ_c⁺, Ξ_c⁰ and, for the first time, Ξ_c⁺, and of the strongly-decaying J/ψ mesons. The first measurements of Ξ_c⁺ and Σ_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 cc¯ production cross section at midrapidity is found to be at the upper bound of state-of-the-art perturbative QCD calculations.