Ratios of heavy baryons to heavy mesons in relativistic nucleus-nucleus collisions

Heavy baryon/meson ratios Λ_c/D⁰ and Λ_b/B̅ ⁰ in relativistic heavy ion collisions are studied in the quark coalescence model. For heavy baryons, we include production from coalescence of heavy quarks with free light quarks as well as with bounded light diquarks that might exist in the strongly coupled quark-gluon plasma produced in these collisions. Including the contribution from decays of heavy hadron resonances and also that due to fragmentation of heavy quarks that are left in the system after coalescence, the resulting Λ_c/D⁰ and Λ_b/B̅ ⁰ ratios in midrapidity (|y|⩽0.5) from central Au+Au collisions at √s_NN=200 GeV are about a factor of five and ten, respectively, larger than those given by the thermal model, and about a factor of ten and twelve, respectively, larger than corresponding ratios in the PYTHIA model for pp collisions. These ratios are reduced by a factor of about 1.6 if there are no diquarks in the quark-gluon plasma. The transverse momentum dependence of the heavy baryon/meson ratios is found to be sensitive to the heavy quark mass, with the Λ_b/B̅ ⁰ ratio being much flatter than the Λ_c/D⁰ ratio. The latter peaks at the transverse momentum p_T≃0.8 GeV but the peak shifts to p_T≃2 GeV in the absence of diquarks.