Observation of orbitally excited $B_c^{+}$ states

Abstract

The observation of a wide peaking structure in the $B_c^{+}\gamma$ mass spectrum is reported using proton-proton collision data collected by the LHCb detector at center-of-mass energies of $7$, $8$, and $13\text{TeV}$, corresponding to a total integrated luminosity of $9{\text{fb}}^{-1}$. The statistical significance over the background-only hypothesis exceeds seven standard deviations. The width of the observed structure is larger than the expectation from a single-peak hypothesis, and is well described by an effective minimal model consisting of two narrow peaks located at $6704.8\pm 5.5\pm 2.8\pm 0.3\mathrm{Me}\mathrm{V}/c^2$ and $6752.4\pm 9.5\pm 3.1\pm 0.3\mathrm{Me}\mathrm{V}/c^2$. The uncertainty terms are statistical, systematic, and associated to the knowledge of the $B_c^{+}$ mass, respectively. The measured peak locations are in line with theoretical predictions for lowest excited $P$-wave $B_c^{+}$ states, marking the first observation of orbitally excited beauty-charm mesons and providing important insights into the internal dynamics of hadrons containing two heavy quarks.

All figures and tables, along with any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/5250 (LHCb public pages)

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