Λ c + production in Pb–Pb collisions at s NN =5.02 TeV

Abstract

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 S 0 (and charge conjugate) in the transverse momentum and centrality intervals 6<p T <12 GeV/c and 0–80%. The Λ 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 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 + /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 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 D 0 <R AA D s + <R AA Λ c + ), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium. © 2019 European Organization for Nuclear Research