Using an $e^{ +}e^{ -}$ annihilation data sample corresponding to an integrated luminosity of $3.19~\mathrm{ fb}^{ -1}$ and collected at a center-of-mass energy $\sqrt{ s} = 4.178~\mathrm{ GeV}$ with the BESIII detector, we measure the absolute branching fractions $\mathcal{ B}(D_{ s}^{ +} \rightarrow K_{ S}^{ 0}K^{ +}) = (1.425\pm0.038_{ \rm stat.}\pm0.031_{ \rm syst.})\%$ and $\mathcal{ B}(D_{ s}^{ +} \rightarrow K_{ L}^{ 0}K^{ +}) =(1.485\pm0.039_{ \rm stat.}\pm0.046_{ \rm syst.})\%$. The branching fraction of $D_{ s}^{ +} \rightarrow K_{ S}^{ 0}K^{ +}$ is compatible with the world average and that of $D_{ s}^{ +} \rightarrow K_{ L}^{ 0}K^{ +}$ is measured for the first time. We present the first measurement of the $K_{ S}^{ 0}$-$K_{ L}^{ 0}$ asymmetry in the decays $D_{ s}^{ +} \rightarrow K_{ S,L}^{ 0}K^{ +}$, and $R(D_{ s}^{ +} \rightarrow K_{ S,L}^{ 0}K^{ +})=\frac{ \mathcal{ B}(D_{ s}^{ +} \rightarrow K_{ S}^{ 0}K^{ +}) -\mathcal{ B}(D_{ s}^{ +} \rightarrow K_{ L}^{ 0}K^{ +})}{ \mathcal{ B}(D_{ s}^{ +} \rightarrow K_{ S}^{ 0}K^{ +}) +\mathcal{ B}(D_{ s}^{ +} \rightarrow K_{ L}^{ 0}K^{ +})}= (-2.1\pm1.9_{ \rm stat.}\pm1.6_{ \rm syst.})\%$. In addition, we measure the direct $CP$ asymmetries $A_{ \rm CP}(D_{ s}^{ \pm} \rightarrow K_{ S}^{ 0}K^{ \pm}) = (0.6\pm2.8_{ \rm stat.}\pm0.6_{ \rm syst.})\%$ and $A_{ \rm CP}(D_{ s}^{ \pm} \rightarrow K_{ L}^{ 0}K^{ \pm}) = (-1.1\pm2.6_{ \rm stat.}\pm0.6_{ \rm syst.})\%$.
Categories: hep-ex