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$Λ_\mathrm{c}^+$ production in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

A measurement of the production of prompt $\Lambda_{\rm c}^{+}$ baryons in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02 $ TeV with the ALICE detector at the LHC is reported. The $\Lambda_{\rm c}^{+}$ and $\overline{\Lambda}_{\rm c}^{-}$ were reconstructed at midrapidity ($|y| <~ 0.5$) via the hadronic decay channel $\Lambda_{\rm c}^{+}\rightarrow {\rm p} {\rm K}_{\rm S}^{0}$ (and charge conjugate) in the transverse momentum and centrality intervals $6 <~ p_{\rm T} <~12$ GeV/$c$ and 0-80%. The $\Lambda_{\rm c}^{+}$/D$^0$ ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02 $ TeV. In particular, the values in p-Pb and Pb-Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties. The $\Lambda_{\rm c}^{+}$/D$^0$ ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The $\Lambda_{\rm c}^{+}$ nuclear modification factor, $R_{\rm AA}$, is also presented. The measured values of the $R_{\rm AA}$ of $\Lambda_{\rm c}^{+}$, D$_{\rm s}$ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy $(R_{\rm AA}^{{\rm D}^{0}}<~R_{\rm AA}^{{\rm D}_{\rm s}}<~R_{\rm AA}^{\Lambda_{\rm c}^{+}})$, conceivable with a contribution of recombination mechanisms to charm hadron formation in the medium.

 

Submitted to: PLB
e-Print: arXiv:1809.10922 | PDF | inSPIRE

Figures

Figure 1

Invariant-mass distributions for the $\Lc$ (left) and $\Dzero$ (right) candidates in the momentum interval $ 6 < \pt< 12$~\gevc and for the 0--80\% centrality class. The dashed curves represent the fit to the background, while the solid curves represent the total fit function.
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Figure 2

$\LcOverDzero$ ratio as a function of $\pt$ in 0--80\% most central Pb--Pb collisions compared with the measurements in pp and p--Pb collisions~ (left), and model calculations~ (right). Statistical and systematic uncertainties are presented as vertical bars and boxes, respectively.
[png]   [pdf]   [eps]

Figure 3

$\RAA$ of prompt $\Lcplus$ compared with model calculations~ (left), and the non-strange D mesons, $\Ds$, and charged particle $\RAA$ in 0--10\% most central Pb--Pb collisions for $\pt > 1~\gevc$~ (right). Statistical, systematic and normalisation uncertainties are presented as vertical bars, empty boxes and shaded boxes around unity, respectively.
[png]   [pdf]   [eps]