The LHC Collaborations reported measurements of the baryon-to-meson ratios for open charm and bottom hadrons in pp, p-Pb and, to some extent, Pb-Pb collisions at the LHC that challenge the present understanding of heavy-quark hadronization in hadronic collisions. The Lambda_c/D, Xi_c/D and Lambda_b/B ratios at low momentum are larger than those measured in e+e– and ep collisions at LEP and HERA and predicted by event generators based on string fragmentation and tuned to describe the LEP and HERA data. The Lambda_c/D ratio in pp and p-Pb collisions is remarkably similar to the Lambda/K ratio and both are larger than the p/pi ratio.
These findings show that the baryon-to-meson ratio depends on the collision system, highlighting the relevance of “long-distance” effects in heavy-quark hadronization. Various QCD mechanisms are recently being considered in the theory community to describe the observations, including colour reconnection, ropes, or statistical approaches. Such effects also have an impact on the measurement of the total heavy-quark production cross section and on the usage of D and B meson production measurements to constrain the PDFs in the proton and in the nucleus.
In nucleus-nucleus collisions, where a hot and dense quark-gluon plasma forms and collectively expands, the enhancement of baryon-to-meson ratios is predicted by theoretical models in which heavy quarks with low momentum hadronize by coalescence with light quarks from the plasma. The first measurements of Lambda_c production in nucleus-nucleus at the LHC (and at RHIC) hint at a larger ratio to D mesons, with respect to the case of pp collisions.
The goals of the proposed workshop are:
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The workshop is co-sponsored by the STRONG 2020 project (EU Horizon 2020 grant 824093).