Charm-baryon production in proton-proton collisions

Recent measurements of charm-hadron production in proton-proton collisions at the LHC have found a surprisingly large baryon to meson ratio. We propose that this observation can be explained by the statistical hadronization model (SHM), by employing a largely augmented set of charm-baryon states beyond the current listings of the particle data group. We estimate the additional states using guidance from the relativistic quark model and from lattice QCD. Using charm- and strange-quark fugacity factors to account for the well-known suppression of heavy flavor in elementary collisions, we compute the yields and spectra of D, Ds and Λc hadrons in proton-proton collisions at s=5 TeV. Our main finding is that the enhanced feeddown from excited charm baryons can account for the Λc/D0 ratio measured by ALICE at midrapidity, with some caveat for the forward-rapidity LHCb data. Furthermore, assuming independent fragmentation of charm quarks but with the hadronic ratios fixed by the SHM, the measured transverse-momentum (pT) spectra of D-mesons and Λc can also be described; in particular, the low-pT enhancement in the observed Λc/D0 ratio is attributed to the enhanced feeddown from “missing” charm-baryon states. We comment on the implications of these findings for measurements of Ds and Λc in heavy-ion collisions.

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