Observation of the B-c(+) Meson in Pb-Pb and pp Collisions at root s(NN)=5.02 TeV and Measurement of its Nuclear Modification Factor

Abstract

The Bþ c meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the Bþ c meson in lead-lead (Pb-Pb) and proton-proton (pp) collisions at a centerof-mass energy per nucleon pair of ffiffiffiffiffiffiffiffi sNN p ¼ 5.02 TeV, via the Bþ c → ðJ=ψ → μþμ−Þμþνμ decay. The Bþ c nuclear modification factor, derived from the Pb-Pb–to–pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the Pb-Pb collision centrality. The Bþ c meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.