Observation of an Excited Bc+/- Meson State with the ATLAS Detector

Abstract

A search for excited states of the B c meson is performed using 4.9 fb−1 of 7 TeV and 19.2 fb−1 of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay B c → J=ψπ . The state appears in the mðB c πþπ−Þ − mðB c Þ − 2mðπ Þ mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842 4 5 MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the B c meson, B c ð2SÞ.