$\rm Λ_{c}^{+}$ production and baryon-to-meson ratios in pp and p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV at the LHC

The prompt production of the charm baryon $\rm \Lambda_{c}^{+}$ and the $\rm \Lambda_{c}^{+}/\mathrm {D^0}$ production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$TeV. These new measurements show a clear decrease of the $\rm \Lambda_{c}^{+}/\mathrm {D^0}$ ratio with increasing transverse momentum ($p_{\rm T}$) in both collision systems in the range $2<~p_{\rm T}<~12$ GeV/$c$, exhibiting similarities with the light-flavour baryon-to-meson ratios ${\rm p}/\pi$ and $\Lambda/\mathrm {K^0_S}$. At low $p_{\rm T}$, predictions that include additional colour-reconnection mechanisms beyond the leading-colour approximation; assume the existence of additional higher-mass charm-baryon states; or include hadronisation via coalescence can describe the data, while predictions driven by charm-quark fragmentation processes measured in $\mathrm {e^+e^-}$ and $\mathrm {e^-p}$ collisions significantly underestimate the data. The results presented in this letter provide significant evidence that the established assumption of universality (colliding-system independence) of parton-to-hadron fragmentation is not sufficient to describe charm-baryon production in hadronic collisions at LHC energies.

 

Phys. Rev. Lett. 127 (2021) 202301
HEP Data
e-Print: arXiv:2011.06078 | PDF | inSPIRE
CERN-EP-2020-217

Figure 1

Left: Prompt \Lcplus and \Dzero \pt-differential cross section in pp collisions and in \pPb collisions at~\sqrtsNNfive. The results in \pPb collisions are scaled with the atomic mass number $A$ of the Pb nucleus. Right: the \LcD ratio as a function of \pt measured in pp collisions at \sqrtsfive compared with theoretical predictions (see text for details). Statistical uncertainties are shown as vertical bars, while systematic uncertainties are shown as boxes, and the bin widths are shown as horizontal bars.

Figure 2

The charm baryon-to-meson ratio \LcD in pp collisions (left), and \pPb collisions (right) at \sqrtsNNfive, compared to the light-flavour baryon-to-meson ratios $\Lambda / \Kzs$ and $\proton/\pi$. Statistical uncertainties are shown as vertical bars, while systematic uncertainties are shown as boxes, and the bin widths are shown as horizontal bars.