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

Abstract

Signals consistent with the B${}_{\mathrm{c}}^{+}$(2S) and B${}_{\mathrm{c}}^{\ast +}$(2S) states are observed in proton-proton collisions at $\sqrt{s}=$ 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 $\bar{\mathrm{b}}$c states are observed in the B${}_{\mathrm{c}}^{+}{\pi }^{+}{\pi }^{-}$ invariant mass spectrum, with the ground state B${}_{\mathrm{c}}^{+}$ reconstructed through its decay to J/$\psi {\pi }^{+}$. The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 $\pm$ 1.5 (stat) $\pm$ 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${}_{\mathrm{c}}^{+}$(2S) meson is measured to be 6871.0 $\pm$ 1.2 (stat) $\pm$ 0.8 (syst) $\pm$ 0.8 (B${}_{\mathrm{c}}^{+}$) MeV, where the last term corresponds to the uncertainty in the world-average B${}_{\mathrm{c}}^{+}$ mass.

arXiv commentReplaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/BPH-18-007 (CMS Public Pages)

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