Multiplicity dependence of ${\mathrm{\Xi }}_c^{+}$ and ${\mathrm{\Xi }}_c^0$ production in pp collisions at $\sqrt{s}=13$ TeV

The first measurement at midrapidity ($\mathrm{\mid }y\mathrm{\mid }<0.5$) of the production yield of the strange-charm baryons ${\mathrm{\Xi }}_c^{+}$ and ${\mathrm{\Xi }}_c^0$ as a function of transverse momentum ($p_{\mathrm{T}}$) in different charged-particle multiplicity classes in proton-proton collisions at $\sqrt{s}=13$ TeV with the ALICE experiment at the LHC is reported. The ${\mathrm{\Xi }}_c^{+}$ baryon is reconstructed via the ${\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}$ decay channel in the range $4<p_{\mathrm{T}}<12$ GeV/$c$, while the ${\mathrm{\Xi }}_c^0$ baryon is reconstructed via both the ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$ and ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{e}^{+}{\nu }_e$ decay channels in the range $2<p_{\mathrm{T}}<12$ GeV/$c$. The baryon-to-meson (${\mathrm{\Xi }}_c^{0,+}\mathrm{/}{\mathrm{D}}^0$) and the baryon-to-baryon (${\mathrm{\Xi }}_c^{0,+}\mathrm{/}{\mathrm{\Lambda }}_{\mathrm{c}}^{+}$) 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(${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{e}^{+}{\nu }_e$)/BR(${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$) is measured as 0.825 $\pm$ 0.094 (stat.) $\pm$ 0.081 (syst.). This value supersedes the previous ALICE measurement, improving the statistical precision by a factor of 1.6.