Observation of Bₚ⁰ mesons and measurement of the Bₚ⁰ /B⁺ yield ratio in PbPb collisions at ? TeV

The B _s ⁰ and B ⁺ production yields are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected with the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb ⁻¹. The mesons are reconstructed in the exclusive decay channels B→s0J/ψ(μ ⁺μ ⁻)ϕ(K ⁺K ⁻) and B→+J/ψ(μ ⁺μ ⁻)K ⁺, in the transverse momentum range 7–50 GeV/c and absolute rapidity 0–2.4. The B _s ⁰ meson is observed with a statistical significance in excess of five standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as functions of the transverse momentum of the B mesons and of the PbPb collision centrality. The ratio of production yields of B _s ⁰ and B ⁺ is measured and compared to theoretical models that include quark recombination effects.