Enhanced Charm Baryon Production and Its Rapidity Dependence in the Statistical Hadronization Model

Measurements of charm baryon-to-meson ratios in pp collisions at midrapidity at the Large Hadron Collider have shown significantly larger values compared to previous measurements in e⁺e^- and ep collisions. This posed a challenge for the assumed universality of fragmentation functions and has sparked widespread interests in the community. In this work, we incorporate unobserved excited baryons from the constituent quark model into the Statistical Hadronization Model, which enhances the charm baryon production. Furthermore, we attribute the reduced charm baryon-to-meson ratios in e⁺e^- and ep collisions than those in pp collisions to canonical suppression due to the small system size, rather than changes in fragmentation functions. By relating system size to the charged-particle density, we calculate the production yields and transverse momentum spectra of charm hadrons at different collision systems and energies. We also exploit the dependence of the system size on rapidity to explain the different Λ_c⁺/D⁰ ratios at middle and forward rapidities measured at the LHC.