Observation of two excited B+c states and measurement of the B+c(2S) mass in pp collisions at s = 13 TeV
Abstract
Signals consistent with the B+c(2S) and B*+c(2S) states are observed in proton-proton collisions at s = 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb-1, collected by the CMS experiment during the 2015-2018 LHC running periods. These excited bc states are observed in the B+cπ+π- invariant mass spectrum, with the ground state B+c reconstructed through its decay to J/\,π+. The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 1.5 (stat) 0.7 (syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B+c(2S) meson is measured to be 6871.0 1.2 (stat) 0.8 (syst) 0.8 (B+c) MeV, where the last term corresponds to the uncertainty in the world-average B+c mass.
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