Multiplicity dependence of Ξ⁺_c and Ξ⁰_c production in pp collisions at √s =13 TeV

The first measurement at midrapidity (|y| < 0.5) of the production yield of the strange-charm baryons Ξ⁺_c and Ξ⁰_c as a function of transverse momentum (p_T) in different charged-particle multiplicity classes in proton-proton collisions at √s = 13 TeV with the ALICE experiment at the LHC is reported. The Ξ⁺_c baryon is reconstructed via the Ξ⁺_c → Ξ⁻π⁺π⁺ decay channel in the range 4 < p_T < 12 GeV/c, while the Ξ⁰_c baryon is reconstructed via both the Ξ⁰_c → Ξ⁻π⁺ and Ξ⁰_c → Ξ⁻e⁺ν_e decay channels in the range 2 < p_T < 12 GeV/c. The baryon-to-meson (Ξ^0,+_c /D⁰) and the baryon-to-baryon (Ξ^0,+_c /Λ⁺_c) production yield ratios show no significant dependence on multiplicity. In addition, the observed yield ratios are not described by theoretical predictions that model charm-quark fragmentation based on measurements at e⁺e⁻ and e⁻p colliders, indicating differences in the charm-baryon production mechanism in pp collisions. A comparison with different event generators and tunings, including different modelling of the hadronisation process, is also discussed. Moreover, the branching-fraction ratio of BR (Ξ⁰_c → Ξ⁻e⁺ν_e) /BR (Ξ⁰_c → Ξ⁻π⁺) is measured as 0.825 ±0 .094 (stat.) ± 0.081 (syst.). This value supersedes the previous ALICE measurement, improving the statistical precision by a factor of 1.6.