Research Papers in Physics and Astronomy


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PHYSICAL REVIEW LETTERS 122, 132001 (2019). DOI: 10.1103/PhysRevLett.122.132001


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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.

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