Angular analysis of $B\to K^{\ast }{e}^{+}{e}^{-}$ in the low-$q^2$ region with new electron identification at Belle

Abstract

We perform an angular analysis of the $B\to K^{\ast }{e}^{+}{e}^{-}$ decay for the dielectron mass squared, $q^2$, range of $0.0008$ to $1.1200{\text{GeV}}^2/c^4$ using the full Belle data set in the $K^{\ast 0}\to K^{+}\ddot{I}{€}^{-}$ and $K^{\ast +}\to K_S^0\ddot{I}{€}^{+}$ channels, incorporating new methods of electron identification to improve the statistical power of the data set. This analysis is sensitive to contributions from right-handed currents from physics beyond the Standard Model by constraining the Wilson coefficients ${\mathcal{C}}_7^{(\prime )}$. We perform a fit to the $B\to K^{\ast }{e}^{+}{e}^{-}$ differential decay rate and measure the imaginary component of the transversality amplitude to be $A_T^{\mathrm{Im}}=-1.27\pm 0.52\pm 0.12$, and the $K^{\ast }$ transverse asymmetry to be $A_T^{(2)}=0.52\pm 0.53\pm 0.11$, with $F_L$ and $A_T^{\mathrm{Re}}$ fixed to the Standard Model values. The resulting constraints on the value of ${\mathcal{C}}_7^{\prime }$ are consistent with the Standard Model within a $2\ddot{I}ƒ$ confidence interval.

Accepted by PRD