Observation of the Singly Cabibbo Suppressed Decay ?c+ ?np+

Abstract

The singly Cabibbo-suppressed decay ?c+?np+ is observed for the first time with a statistical significance of 7.3s by using 3.9 fb-1 of e+e-collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of ?c+?np+ is measured to be (6.6±1.2stat±0.4syst)×10-4. By taking the upper limit of branching fractions of ?c+?pp0 from the Belle experiment, the ratio of branching fractions between ?c+?np+ and ?c+?pp0 is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with most predictions of the available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays ?c+?p+ and ?c+?0p+ are measured to be (1.31±0.08stat±0.05syst)×10-2 and (1.22±0.08stat±0.07syst)×10-2, respectively, which are consistent with previous results.