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

TL;DR

This paper reports the first measurement of $\\Xi_c^+$ and $\\Xi_c^0$ baryon production in proton-proton collisions at 13 TeV, revealing no significant multiplicity dependence and challenging existing charm-quark fragmentation models.

Contribution

It provides the first detailed measurement of strange-charm baryon yields as a function of multiplicity in pp collisions at 13 TeV, including decay channels and branching ratios, with implications for hadronization models.

Findings

No significant multiplicity dependence of baryon-to-meson ratios.

Observed yield ratios differ from theoretical predictions based on $e^+e^-$ and $e^-$p data.

Measured branching-fraction ratio of $\\Xi_c^0$ decays with improved precision.

Abstract

The first measurement at midrapidity ($|y| < 0.5$) of the production yield of the strange-charm baryons $\Xi_c^+$ and $\Xi_c^0$ as a function of transverse momentum ($p_{\rm T}$) 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 $\Xi_c^+$ baryon is reconstructed via the $\Xi_c^+ \rightarrow \Xi^-\pi^+\pi^+$ decay channel in the range $4 < p_{\rm T} < 12$ GeV/$c$, while the $\Xi_c^0$ baryon is reconstructed via both the $\Xi_c^0 \rightarrow \Xi^-\pi^+$ and $\Xi_c^0 \rightarrow \Xi^-e^+\nu_e$ decay channels in the range $2 < p_{\rm T} < 12$ GeV/$c$. The baryon-to-meson ($\Xi_c^{0,+}/{\rm D}^0$) and the baryon-to-baryon ($\Xi_c^{0,+}/\Lambda_{\rm c}^+$) 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($\Xi_c^0 \rightarrow \Xi^-e^+\nu_e$)/BR($\Xi_c^0 \rightarrow \Xi^-\pi^+$) 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.