Abstract
A measurement of the production of prompt Λc+ baryons in Pb–Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC is reported. The Λc+ and Λ‾c− were reconstructed at midrapidity (|y|<0.5) via the hadronic decay channel Λc+→pKS0 (and charge conjugate) in the transverse momentum and centrality intervals 6<pT<12 GeV/c and 0–80%. The Λc+/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 sNN=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 pT interval covered by the measurements in the two collision systems. The Λc+/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 Λc+ nuclear modification factor, RAA, is also presented. The measured values of the RAA of Λc+, Ds+ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy (RAAD0<RAADs+<RAAΛc+), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium.
Highlights
Measurements of the production of open-heavy flavour hadrons in heavy-ion collisions provide important information on the properties of the Quark–Gluon Plasma (QGP), the state of stronglyinteracting matter formed at the very high temperatures and energy densities reached in heavy-ion collisions [1,2]
Several measurements of the production and elliptic flow of D mesons and leptons from the decay of heavy-flavour hadrons in Pb–Pb collisions at the LHC and in Au–Au collisions at RHIC [3,4] indicate that charm quarks interact strongly with the medium constituents
Inmedium energy loss is studied via the nuclear modification factor, RAA, defined as the ratio of the yield in Pb–Pb collisions and that in pp collisions scaled by the number of binary nucleon–nucleon collisions
Summary
Measurements of the production of open-heavy flavour hadrons in heavy-ion collisions provide important information on the properties of the Quark–Gluon Plasma (QGP), the state of stronglyinteracting matter formed at the very high temperatures and energy densities reached in heavy-ion collisions [1,2]. A model [5,6] including a significant fraction of low and intermediate transverse momentum (pT) charm and beauty quarks hadronising via coalescence (or recombination) with light quarks from the medium better describes the experimental results. Models including coalescence predict an enhanced baryon-to-meson ratio at low and intermediate transverse momentum in comparison to that expected in pp collisions. This effect adds to the hadron-mass dependent transversemomentum shift due to the presence of radial flow in heavy-ion collisions, that is able to explain the observed increase of the baryon-to-meson ratio in the light sector up to about 2 GeV/c [8]. The D0-meson yield was obtained in the same transverse momentum and centrality interval as the c-baryon, following the analysis procedure described in Ref. [18]
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