Observation of Two Excited Bc+ States and Measurement of the Bc+ (2S) Mass in pp Collisions at s =13 TeV

Abstract

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+?+?- invariant mass spectrum, with the ground state Bc+ reconstructed through its decay to J/??+. 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. � 2019 CERN for the CMS Collaboration. Published by the American Physical Society under the terms of the �https://creativecommons.org/licenses/by/4.0/� Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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