Observation of an excited B±c meson state with the ATLAS detector

Abstract

A search for excited states of the B+/- c meson is performed using 4.9fb -1 of 7 TeV and 19.2fb -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/psi pi +/-. The state appears in the m(B+/- c pi+pi -)- m(B+/- c)-2m(pi +/-) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842+/-4+/-5MeV, 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(2S).