Enhanced Production of Λ_b⁰ Baryons in High-Multiplicity pp Collisions at √s =13 TeV

The production rate of Λ_b⁰ baryons relative to B⁰ mesons in pp collisions at a center-of-mass energy √s=13 TeV is measured by the LHCb experiment. The ratio of Λ_b⁰ to B⁰ production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in e⁺e^- collisions, and increases by a factor of ∼2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λ_b⁰ to B⁰ cross sections is higher than what is measured in e⁺e^- collisions, but converges with the e⁺e^- ratio as the momentum increases. These results imply that the evolution of heavy b quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed.