Measurement of $C\text{\hspace{0.17em}⁣}P$ asymmetries in the decays $B^0\to K^{\ast 0}{\mu }^{+}{\mu }^{-}$ and $B^{+}\to K^{+}{\mu }^{+}{\mu }^{-}$

The direct $C\text{\hspace{0.17em}⁣}P$ asymmetries of the decays $B^0 \rightarrow K^{*0} \mu^+ \mu^-$and$B^+ \rightarrow K^{+} \mu^+ \mu^-$aremeasuredusing$pp$collisiondatacorrespondingtoanintegratedluminosityof3.0$\mbox{fb}^{-1}$collectedwiththeLHCbdetector\mathrm{.}Therespectivecontrolmodes$B^0 \rightarrow J/\psi K^{*0}$and$B^+ \rightarrow J/\psi K^{+}$ are used to account for detection and production asymmetries. The measurements are made in several intervals of ${\mu }^{+}{\mu }^{-}$ invariant mass squared, with the $\varphi (1020)$ and charmonium resonance regions excluded. Under the hypothesis of zero $C\text{\hspace{0.17em}⁣}P$ asymmetry in the control modes, the average values of the asymmetries are \begin{align} {\cal A}{C!P}(B^0 \rightarrow K^{*0} \mu^+ \mu^-) &= -0.035 \pm 0.024 \pm 0.003, \cr {\cal A}{C!P}(B^+ \rightarrow K^{+} \mu^+ \mu^-) &= \phantom{-}0.012 \pm 0.017 \pm 0.001, \end{align} where the first uncertainties are statistical and the second are due to systematic effects. Both measurements are consistent with the Standard Model prediction of small $C\text{\hspace{0.17em}⁣}P$ asymmetry in these decays.