Charm-baryon production in proton-proton collisions

Abstract

Recent measurements of charm-baryon production in proton-proton collisions at the LHC have found a surprisingly large yield relative to those of D-mesons. 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, D s and Λ c 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 Λ c /D 0 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 transversemomentum (p T ) spectra of D-mesons and Λ c can also be described; in particular, the low-p T enhancement in the observed Λ c /D 0 ratio is attributed to the enhanced feeddown from "missing" charm-baryon states. We comment on the implications of these findings for measurements of D s and Λ c in heavy-ion collisions.

Charmed hadron production in an improved quark coalescence model

“…This then leads to a yield of 0.547 for Λ + c and 0.175 for Ξ c as shown in Table V. The total integrated yield ratio Λ + c /D 0 is then about 0.64, which is slightly larger than the value of about 0.54 measured in p + p collisions at √ s = 7 TeV at LHC [21,48]. We note that the oscillator constant used here for charmed baryons is larger than that for charmed mesons, which is different from that in Ref.…”

QCD challenges from pp to A–A collisions

“…For non-strange D-mesons (D and D * ), the hadrochemistry does not show significant variations from pp to p-Pb and Pb-Pb collisions, and essentially follows that of a statistical hadronization with relative weights given by thermal factors at a "hadronization temperature" of T H 160 MeV. The D s /D ratio is also compatible with this pattern, once a strangeness suppression factor of γ s 0.6, as independently inferred from strange-particle production, is accounted for in pp collisions [150]. In semi-/central A-A collisions γ s is close to 1 (which is believed to be a consequence of strangeness equilibration in the QGP fireball), and the expected increase of the D s /D ratio in A-A collisions [151][152][153] is indeed compatible with experimental observations [154].…”

“…In Ref. [150] it was shown that upon including a largely augmented charm-baryon spectrum as predicted by relativistic quark models (also consistent with lQCD [157]), the ALICE measurement could be accounted for. Improvements in the string fragmentation scenario, by accounting for color correlations beyond the leading-color approximation to create several MPI subsystems, can also facilitate the formation of charm baryons in pp collisions [113], yielding a Λ c /D 0 ratio close to that measured at midrapidity.…”

Improvement of heavy flavor production in a multiphase transport model updated with modern nuclear parton distribution functions

“…On the other hand, the r BM value for heavy flavor hadrons is set to 1.00, because the light flavor value of 0.53 would lead to too few charm baryons (by a factor of ∼ 4) compared to the experimental data in pp or AA collisions. In principle, the r BM value for charm hadrons is related to the properties such as the number and masses of available charm baryon states versus charm meson states, and the higher r BM value for charm is consistent with the assumption that relative to light flavors there are more charm baryon states than charm meson states [40].…”