Observation of two excited B$^+_\mathrm{c}$ states and measurement of the B$^+_\mathrm{c}$(2S) mass in pp collisions at $\sqrt{s} =$ 13 TeV
Signals consistent with the Bc(2S) and Bc(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 Bc π+π− invariant mass spectrum, with the ground state Bc reconstructed through its decay to J/ψ 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 Bc(2S) meson is measured to be 6871.0± 1.2 (stat)± 0.8 (syst)± 0.8 (Bc)MeV, where the last term corresponds to the uncertainty in the world-average Bc mass. Published in Physical Review Letters as doi:10.1103/PhysRevLett.122.132001. c © 2019 CERN for the benefit of the CMS Collaboration. CC-BY-4.0 license ∗See Appendix A for the list of collaboration members ar X iv :1 90 2. 00 57 1v 3 [ he pex ] 3 A pr 2 01 9