PNNL

Abstract

The first measurements of the coherence factor RK0 SK_ and the average strong–phase difference _K0SK_D in D0 ? K0S K±_± decays are reported. These parameters can be used to improve the determination of the unitary triangle angle in B- ? eD K- decays, where eD is either a D0 or a D0 meson decaying to the same final state, and also in studies of charm mixing. The measurements of the coherence factor and strong–phase difference are made using quantum–correlated, fully– reconstructed D0D0 pairs produced in e+e- collisions at the (3770) resonance. The measured values are RK0 SK_ = 0.73} 0.08 and _K0SK_ D = (8.3} 15.2)? for an unrestricted kinematic region and RK*K = 1.00} 0.16 and _K*KD = (26.5 } 15.8)? for a region where the combined K0S_±invariant mass is within 100 MeV/c2 of the K*(892)± mass. These results indicate a significant level of coherence in the decay. In addition, isobar models are presented for the two decays, which show the dominance of the K*(892)± resonance. The branching ratio B(D0 ? K0S K+_-)/B(D0 ? K0S K-_+) is determined to be 0.592} 0.044 (stat.)} 0.018 (syst.), which is more precise than previous measurements.