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 charged-particle multiplicity 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 ($\Xi_c^{0,+}/D^0$) and the baryon-to-baryon ($\Xi_c^{0,+}/\Lambda_c^+$) 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.
JHEP 12 (2025) 038
HEP Data
e-Print: arXiv:2508.09955 | PDF | inSPIRE
CERN-EP-2025-175
Figure group
Figure 1
Invariant-mass distributions of signal candidates for the hadronic decays of $\Xi_c^+$ in $4 < p_{\rm T} < 12$ GeV/$c$ (left), and $\Xi_c^0$ in $2 < p_{\rm T} < 12$ GeV/$c$ (right), in the high-multiplicity class. The blue solid curve shows the total fit, and the red dashed curve shows the combinatorial background. |   |
Figure 2
Invariant-mass distribution of $\rm e\Xi$ pairs for $\Xi_{\rm c}^{0} \rightarrow \Xi^- {\rm e}^+ \rm \nu_{\rm e}$ in $4 < p_{\rm T} < 6$ GeV/$c$, in the high- (left) and low- (right) multiplicity classes. The blue filled distribution shows the total fit and the coloured lines indicate the different sources contributing to the fit. |   |
Figure 3
p$_{\rm T}$-differential per-event yield of prompt $\Xi_c^0$ (left) and $\Xi_c^+$ (right) baryons measured in the different multiplicity classes in pp collisions at $\sqrt{s}=13$ TeV at midrapidity ($|y| < 0.5$), along with the corresponding ratios to the multiplicity-integrated (INEL $>$ 0) class in the bottom panel. The statistical and systematic uncertainties are shown as bars and open boxes, respectively. The shaded boxes indicate the uncertainty of the branching ratio. |  |
Figure 4
The prompt production yield ratios between $\Xi_{\rm c}^{0,+}$ and $\rm D^{0}$ mesons (top) and $\Xi_{\rm c}^{0,+}$ and $\Lambda_{\rm c}^{+}$ baryons (bottom) measured in the same multiplicity classes in pp collisions at $\sqrt{s}=13$ TeV. The statistical and systematic uncertainties are shown as bars and open boxes, and the uncertainty from BR is represented in shaded boxes, respectively. |  |
Figure 5
The baryon-to-meson ratios (top) and baryon-to-baryon ratios (bottom), measured in the low- (left) and high- (right) multiplicity classes. The measurements are compared with the predictions from two event generators: PYTHIA 8 with different tunes (namely Monash, CR-BLC Mode 0, 2, and 3) and EPOS4HQ. |  |
