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

The production rate of Λb0 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 Λb0 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 Λb0 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.