Observation of Two Excited B\u3csup\u3e+\u3c/sup\u3e\u3csub\u3ec\u3c/sub\u3e States and Measurement of the B\u3csup\u3e+\u3c/sup\u3e\u3csub\u3ec\u3c/sub\u3e (2S) Mass in \u3ci\u3epp\u3c/i\u3e 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 []c states are observed in the B+c π+π− invariant mass spectrum, with the ground state B+c 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 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