Measurement of the isospin asymmetry in $B\to K^{(\ast )}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ decays

Abstract

The isospin asymmetries of $B\to K^{(\ast )}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ decays and the partial branching fractions of $B^0\to K^0\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ and $B^{+}\to K^{\ast +}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ are measured as a function of the di-muon mass squared $q^2$ using an integrated luminosity of 1.0 fb${}^{-1}$ collected with the LHCb detector. The $B\to K\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ isospin asymmetry integrated over $q^2$ is negative, deviating from zero with over 4 $\ddot{I}ƒ$ significance. The $B\to K^{\ast }\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ decay measurements are consistent with the Standard Model prediction of negligible isospin asymmetry. The observation of the decay $B^0\to K_{\mathrm{S}}^0\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ is reported with 5.7 $\ddot{I}ƒ$ significance. Assuming that the branching fraction of $B^0\to K^0\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ is twice that of $B^0\to K_{\mathrm{S}}^0\hat{I}{¼}^{+}\hat{I}{¼}^{-}$, the branching fractions of $B^0\to K^0\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ and $B\to K^{\ast +}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ are found to be ($0.31_{-0.06}^{+0.07})\times 10^{-6}$ and ($1.16\pm 0.19)\times 10^{-6}$, respectively.

21 pages. Updated to correspond to proof from JHEP