# Observation of Two Excited ${B}_{c}^{+}$ States and Measurement of the ${B}_{c}^{+}\left(2S\right)$ Mass in $pp$ Collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$

09 April 2019

Abstract: Signals consistent with the ${B}_{c}^{+}\left(2S\right)$ and ${B}_{c}^{*+}\left(2S\right)$ states are observed in proton-proton collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$, in an event sample corresponding to an integrated luminosity of $143\text{}\text{}{\mathrm{fb}}^{-1}$, collected by the CMS experiment during the 2015–2018 LHC running periods. These excited $\overline{b}c$ states are observed in the ${B}_{c}^{+}{\pi }^{+}{\pi }^{-}$ invariant mass spectrum, with the ground state ${B}_{c}^{+}$ reconstructed through its decay to $J/\psi {\pi }^{+}$. The two states are reconstructed as two well-resolved peaks, separated in mass by $29.1±1.5\left(\mathrm{stat}\right)±\phantom{\rule{0ex}{0ex}}0.7\left(\mathrm{syst}\right)\text{}\text{}\mathrm{MeV}$. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the ${B}_{c}^{+}\left(2S\right)$ meson is measured to be $6871.0±1.2\left(\mathrm{stat}\right)±0.8\left(\mathrm{syst}\right)±\phantom{\rule{0ex}{0ex}}0.8\left({B}_{c}^{+}\right)\text{}\text{}\mathrm{MeV}$, where the last term corresponds to the uncertainty in the world-average ${B}_{c}^{+}$ mass.

Published in: Physical Review Letters 122 (2019)