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 b¯c states are observed in the Bc+π+π- invariant mass spectrum, with the ground state Bc+ reconstructed through its decay to J/ψπ+. 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.
10.1103_PhysRevLett.122.132001.pdf
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1902.00571.pdf
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