Measurement of Forward-Backward Asymmetry and Wilson Coefficients in $B\to K^{*}{l}^{+}{l}^{-}$

We report the first measurement of the forward-backward asymmetry and the ratios of Wilson coefficients $A_9/A_7$ and $A_{10}/A_7$ in $B\to K^{*}{\ell }^{+}{\ell }^{-}$, where $\ell$ represents an electron or a muon. We find evidence for the forward-backward asymmetry with a significance of $3.4\sigma$. The results are obtained from a data sample containing $386\times {10}^{6}B\overline{B}$ pairs that were collected on the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

Figure 1

$M_{\mathrm{bc}}$ distributions for (a) $B\to K^{*}{\ell }^{+}{\ell }^{-}$ and (b) $B\to K^{+}{\ell }^{+}{\ell }^{-}$ samples. The solid and dashed curves are the fit results for the total and background contributions, respectively.

Figure 2

Fit result for the negative $A_7$ solution (solid line) projected onto the background-subtracted forward-backward asymmetry and forward-backward asymmetry curves for several input parameters, including the effects of efficiency: $A_7$ positive case ($A_7=0.330$, $A_9=4.07$, $A_{10}=-4.21$) (dashed line), $A_{10}$ positive case ($A_7=-0.280$, $A_9=2.42$, $A_{10}=1.32$) (dotted-dashed line), and both $A_7$ and $A_{10}$ positive cases ($A_7=0.280$, $A_9=2.22$, $A_{10}=3.82$) (dotted line) [9]. The new physics scenarios shown by the dotted-dashed and dotted curves are excluded. The blank regions are excluded by the $\psi X_s$ veto.

Figure 3

C.L. contours for negative $A_7$. Curves show $1\sigma –5\sigma$ contours. The symbols show the fit (circle), SM (triangle), and $A_{10}$-positive (star) [9] cases. The $A_{10}$-positive case appears as the dotted-dashed curve of Fig. 2.