Measurements of the mass and width of the η c using the decay ψ(3686)→γη c

Abstract

The mass and width of the lowest-lying S-wave spin singlet charmonium state, the η c, are measured using a data sample of 1.06×108 ψ(3686) decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates full interference between the signal reaction, ψ(3686)→γη c, and a nonresonant radiative background to describe the line shape of the η c successfully. We measure the η c mass to be 2984.3±0.6±0.6MeV/c2 and the total width to be 32.0±1.2±1.0MeV, where the first errors are statistical and the second are systematic. © 2012 American Physical Society.