Enhanced Production of Λb0 Baryons in High-Multiplicity pp Collisions at s=13 TeV

The production rate of Λ0 b baryons relative to B0 mesons in pp collisions at a center-of-mass energy ffiffi s p ¼ 13 TeV is measured by the LHCb experiment. The ratio of Λ0 b 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 eþe− collisions, and increases by a factor of ∼2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λ0 b to B0 cross sections is higher than what is measured in eþe− collisions, but converges with the eþe− ratio as the momentum increases. These results imply that the evolution of heavy b quarks into finalstate 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.