Measurement of the strong-phase difference between D0 and D0 ¯ ?k K-p p- in bins of phase space

A first determination of the strong-phase difference between D0 and D0¯→K+K-π+π- is performed using e+e-→ψ(3770)→DD¯ data collected by the BESIII detector corresponding to an integrated luminosity of 20.3 fb-1. The measurements are made in four pairs of bins in phase space, which are chosen to provide optimal sensitivity to the angle γ of the unitarity triangle in B±→DK± decays. From these measurements, it follows that the CP-even fraction of the decay is F+=0.754±0.010stat±0.008syst. In addition, the branching fraction of D0→K+K-π+π- is measured to be (2.863±0.028stat±0.045syst)×10-3, which is twice as precise as previous results obtained at other experiments.