The transverse momentum ($p_{\rm T}$) differential production cross section of the promptly-produced charm-strange baryon $\Xi_{\rm c}^{0}$ (and its charge conjugate $\overline{\Xi_{\rm c}^{0}}$) is measured at midrapidity via its hadronic decay into ${\rm \pi^{+}}\Xi^{-}$ in p$-$Pb collisions at a centre-of-mass energy per nucleon$-$nucleon collision $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV with the ALICE detector at the LHC. The $\Xi_{\rm c}^{0}$ nuclear modification factor ($R_{\rm pPb}$), calculated from the cross sections in pp and p$-$Pb collisions, is presented and compared with the $R_{\rm pPb}$ of $\Lambda_{\rm c}^{+}$ baryons. The ratios between the $p_{\rm T}$-differential production cross section of $\Xi_{\rm c}^{0}$ baryons and those of $\mathrm {D^0}$ mesons and $\Lambda_{\rm c}^{+}$ baryons are also reported and compared with results at forward and backward rapidity from the LHCb Collaboration. The measurements of the production cross section of prompt $\Xi^0_{\rm c}$ baryons are compared with a model based on perturbative QCD calculations of charm-quark production cross sections, which includes only cold nuclear matter effects in p$-$Pb collisions, and underestimates the measurement by a factor of about 50. This discrepancy is reduced when the data is compared with a model in which hadronisation is implemented via quark coalescence. The $p_{\rm T}$-integrated cross section of prompt $\Xi^0_{\rm c}$-baryon production at midrapidity extrapolated down to $p_{\rm T}$ = 0 is also reported. These measurements offer insights and constraints for theoretical calculations of the hadronisation process. Additionally, they provide inputs for the calculation of the charm production cross section in p$-$Pb collisions at midrapidity.
Submitted to: EPJC
e-Print: arXiv:2405.14538 | PDF | inSPIRE
CERN-EP-2024-140
Figure group
Figure 1
Invariant mass distributions of $\Xi_{\rm c}^{0} \rightarrow {\rm \pi^{+}}\Xi^{-}$ candidates (and charge conjugates) in $2 < \pt < 4$ GeV/$c$ (left), and in $6 < \pt < 8$ GeV/$c$ (right) in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. The red dashed curves represent the background fit functions, and the blue curves represent the total fit functions. |   |
Figure 2
Product of detector acceptance and efficiency for $\Xi_{\rm c}^{0} $ baryons in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV as a function of $\pt$. The solid line corresponds to the $(\mathrm{Acc}\times\epsilon)$ for prompt $\Xi_{\rm c}^{0} $, while the dotted line represents $(\mathrm{Acc}\times\epsilon)$ for $\Xi_{\rm c}^{0} $ baryons originating from beauty-hadron decays. The statistical uncertainties are smaller than the marker size. |  |
Figure 3
Prompt $\Xi_{\rm c}^{0}$-baryon $\pt$-differential cross section in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. The statistical uncertainties are shown as vertical bars and the systematic uncertainties are shown as boxes. Left: comparison to predictions from POWHEG+PYTHIA 6 simulations matched with the EPPS16 nPDF parameterisation and the QCM . The uncertainties on the POWHEG calculation are due to the choice of the pQCD scales and the charm quark mass as described in the text. Right: Comparison with the cross section measured in the semileptonic decay channel in pp collisions at $\sqrt{s}=5.02$ TeV and in the hadronic decay channel in pp collisions at $\sqrt{s}=13$ TeV scaled to $\sqrt{s}=5.02$ TeV (the energy-scaling factor is described in the text). Both the pp measurements are scaled by the atomic mass number A of the Pb nucleus. |   |
Figure 4
Nuclear modification factor $R_\mathrm{pPb}$ of prompt $\Xi_{\rm c}^{0}$ baryons in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV as a function of $\pt$ compared to the $R_\mathrm{pPb}$ of $\Lambda_\mathrm{c}^+$ baryons . The measured $R_\mathrm{pPb}$ is also compared to POWHEG+PYTHIA 6 with EPPS16 simulations and to QCM predictions. The statistical uncertainties are shown as vertical bars and the systematic uncertainties are shown as boxes. The uncertainties on the POWHEG calculation are due to the choice of the pQCD scales as described in the text. |  |
Figure 5
Left: $\Xi_{\rm c}^{0}$/$\mathrm{D}^0$ ratio as a function of $\pt$ in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV and in pp collisions at $\sqrt{s}=5.02$ TeV compared to QCM and POWHEG + PYTHIA 6 predictions. Right: $\Xi_{\rm c}^{0}$/$\Lambda_\mathrm{c}^+$ ratio as a function of $\pt$ in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV and in pp collisions at $\sqrt{s}=13$ TeV compared to QCM and POWHEG + PYTHIA 6 predictions. The BR uncertainties for the $\Lambda_\mathrm{c}^+$ are evaluated as the weighted average on the two decay channels and are included in the systematic uncertainty box for each $\pt$ bin. |   |
Figure 6
$\Xi_{\rm c}^{0}$/$\mathrm{D}^0$ (left) and $\Xi_{\rm c}^{0}$/$\Lambda_\mathrm{c}^+$ (right) ratios as a function of $\pt$ in p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV measured by ALICE, compared to the $\Xi_{\rm c}^{+}$/$\mathrm{D}^0$and the $\Xi_{\rm c}^{+}$/$\Lambda_\mathrm{c}^+$ ratio measured by LHCb at $\sqrt{s_\mathrm{NN}}=8.16$ TeV . |   |