Evidence for X(3872) in PbPb collisions and studies of its prompt production at √SNN = 5.02 TeV with CMS

The first evidence for X(3872) production in relativistic heavy ion collisions, with a significance of 4.2 standard deviations, is reported. The X(3872) production is studied in lead-lead (PbPb) collisions at a center-of-mass energy of √S_NN = 5.02 TeV per nucleon pair with the CMS detector. The measurement is performed in the rapidity and transverse momentum ranges |y| < 1.6 and 15 < p_T< 50 GeV/c. The prompt X(3872) to ψ(2S) yield ratio is found to be ρ^PbPb = 1.08 ± 0.49(stat.) ± 0.52(syst.), to be compared with typical values of 0.1 for pp collisions. This provides new input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state.