Study of the decays D + s → K 0 S K + and K 0 L K +

Using an e+e− annihilation data sample corresponding to an integrated luminosity of 3.19  fb−1 and collected at a center-of-mass energy √s=4.178  GeV with the BESIII detector, we measure the absolute branching fractions B(D+s→K0SK+)=(1.425±0.038stat.±0.031syst.)% and B(D+s→K0LK+)=(1.485±0.039stat.±0.046syst.)%. The branching fraction of D+s→K0SK+ is compatible with the world average and that of D+s→K0LK+ is measured for the first time. We present the first measurement of the K0S−K0L asymmetry in the decays D+s→K0S,LK+, and R(D+s→K0S,LK+)=B(D+s→K0SK+)−B(D+s→K0LK+)B(D+s→K0SK+)+B(D+s→K0LK+)=(−2.1±1.9stat.±1.6syst.)%. In addition, we measure the direct CP asymmetries ACP(D±s→K0SK±)=(0.6±2.8stat.±0.6syst.)% and ACP(D±s→K0LK±)=(−1.1±2.6stat.±0.6syst.)%.