Observation of Orbitally Excited B_{c}^{+} States

The observation of a wide peaking structure in the B_{c}^{+}γ mass spectrum is reported using proton-proton collision data collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9  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±5.5±2.8±0.3  MeV/c^{2} and 6752.4±9.5±3.1±0.3  MeV/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.