Λ_c⁺ production in Pb–Pb collisions at √s_NN = 5.02 TeV

A measurement of the production of prompt Λ_c⁺ baryons in Pb–Pb collisions at √s_NN = 5.02 TeV with the ALICE detector at the LHC is reported. The Λ_c⁺ and Λ‾_c⁻ were reconstructed at midrapidity (|y|<0.5) via the hadronic decay channel Λ_c⁺ → pK_S⁰ (and charge conjugate) in the transverse momentum and centrality intervals 6<p_T <12 GeV/c and 0–80%. The Λ_c⁺/D⁰ 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 √s = 7 TeV and in p–Pb collisions at √s_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 in the common p_T interval covered by the measurements in the two collision systems. The Λ_c⁺/D⁰ 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 Λ_c⁺ nuclear modification factor, R_AA , is also presented. The measured values of the R_AA of Λ_c⁺,D_s⁺ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy (R_AA^D0 < R_AA^D_s+ < R _AA^Λ_c+), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium.