Charm-hadron production in $pp$ and AA collisions

Abstract

Recent measurements of various charm-hadron ratios in $pp$, $p$-Pb and Pb-Pb collisions at the LHC have posed challenges to the theoretical understanding of heavy-quark hadronization. The ${\Lambda }_c/D^0$ ratio in $pp$ and $p$-Pb collisions shows larger values than those found in $e^{+}{e}^{-}$ and $ep$ collisions and predicted by Monte-Carlo event generators based on string fragmentation, at both low and intermediate transverse momenta ($p_T$). In AA collisions, the $D_s/D$ ratio is significantly enhanced over its values in $pp$, while the ${\Lambda }_c/D^0$ data indicates a further enhancement at intermediate $p_T$. Here, we report on our recent developments for a comprehensive description of the charm hadrochemistry and transport in $pp$ and $AA$ collisions. For $pp$ collisions we find that the discrepancy between the ${\Lambda }_c/D^0$ data and model predictions is much reduced by using a statistical hadronization model augmented by a large set of "missing" states in the charm-baryon spectrum, contributing to the ${\Lambda }_c$ via decay feeddown. For $AA$ collisions, we develop a 4-momentum conserving resonance recombination model for charm-baryon formation implemented via event-by-event simulations that account for space-momentum correlations (SMCs) in transported charm- and thermal light-quark distributions. The SMCs, together with the augmented charm-baryon states, are found to play an important role in describing the baryon-to-meson enhancement at intermediate momenta. We emphasize the importance of satisfying the correct (relative) chemical equilibrium limit when computing the charm hadrochemistry and its momentum dependence with coalescence models.

arXiv comment4 pages, 3 figures; Quark Matter 2019 proceedings

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