Charm production and fragmentation fractions at midrapidity in pp collisions at $\sqrt{s}=13$ TeV

Abstract

Measurements of the production cross sections of prompt ${\mathrm{D}}^0$, ${\mathrm{D}}^{+}$, ${\mathrm{D}}^{\ast +}$, ${\mathrm{D}}_{\mathrm{s}}^{+}$, ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$, and ${\mathrm{\Xi }}_{\mathrm{c}}^{+}$ 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 ($p_{\mathrm{T}}$) are provided with improved precision and granularity. The ratios of $p_{\mathrm{T}}$-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 ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ (${\mathrm{\Xi }}_{\mathrm{c}}^{+}$) baryon production extend the measured $p_{\mathrm{T}}$ intervals down to $p_{\mathrm{T}}=0(3)$~GeV$/c$. These measurements are used to determine the charm-quark fragmentation fractions and the $\mathrm{c}\overline{\mathrm{c}}$ production cross section at midrapidity ($|y|<0.5$) based on the sum of the cross sections of the weakly-decaying ground-state charm hadrons ${\mathrm{D}}^0$, ${\mathrm{D}}^{+}$, ${\mathrm{D}}_{\mathrm{s}}^{+}$, ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$, ${\mathrm{\Xi }}_{\mathrm{c}}^0$ and, for the first time, ${\mathrm{\Xi }}_{\mathrm{c}}^{+}$, and of the strongly-decaying J/$psi$ mesons. The first measurements of ${\mathrm{\Xi }}_{\mathrm{c}}^{+}$ and ${\mathrm{\Sigma }}_{\mathrm{c}}^{0,++}$ 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 $\mathrm{c}\overline{\mathrm{c}}$ production cross section at midrapidity is found to be at the upper bound of state-of-the-art perturbative QCD calculations.

47 pages, 13 captioned figures, 7 tables, authors from page 42, published version, figures at http://alice-publications.web.cern.ch/node/9560

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