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

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The prompt production of the charmed 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 charmed-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 charmed-baryon production in hadronic collisions at LHC energies.

 

Submitted to: PRL
e-Print: arXiv:2011.06078 | PDF | inSPIRE
CERN-EP-2020-217

Figure 1

< p>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. Statistical uncertainties are shown as vertical bars, while systematic uncertainties are shown as boxes. Right: the \LcD ratio as a function of \pt measured in pp collisions at \sqrtsfive compared with theoretical predictions (see text for details).< /p>

Figure 2

< p>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.< /p>