Observation of the W -annihilation decay Ds+ ???+ and evidence for Ds+ ??K+

Abstract

We report the observation of W-annihilation decay Ds+???+ and evidence for Ds+??K+ in a data sample corresponding to an integrated luminosity of 3.19 fb-1 collected with the BESIII detector at a center-of-mass energy s=4.178 GeV. We obtain the branching fractions B(Ds+???+)=(1.77±0.32stat±0.13sys)×10-3 with a significance of 6.7? and B(Ds+??K+)=(0.87±0.24stat±0.08sys)×10-3 with a significance of 4.4?. This measurement provides critical information to determine the nonperturbative W-annihilation amplitudes and shows the potential of searching for CP asymmetry in Ds+??K+.