Lepton-Flavor-Dependent Angular Analysis of $B\to K^{*}{\ell }^{+}{\ell }^{-}$

We present a measurement of angular observables and a test of lepton flavor universality in the $B\to K^{*}{\ell }^{+}{\ell }^{-}$ decay, where $\ell$ is either $e$ or $\mu$. The analysis is performed on a data sample corresponding to an integrated luminosity of $711{\mathrm{fb}}^{-1}$ containing $772\times 10^6$ $B\overline{B}$ pairs, collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the asymmetric-energy $e^{+}{e}^{-}$ collider KEKB. The result is consistent with standard model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of $2.6\sigma$.

Figure 1

Distribution of the beam-energy constrained mass for selected $B\to K^{*}{e}^{+}{e}^{-}$ (left) and $B\to K^{*}{\mu }^{+}{\mu }^{-}$ (right). Combinatorial background (shaded blue), signal (red filled), and total (solid) fit functions are superimposed on the data points.

Figure 2

$P_4^{\prime }$ and $P_5^{\prime }$ observables for combined electron and muon modes. The SM predictions are provided by DHMV [9, 23] and lattice QCD [24] and displayed as boxes for the muon modes only. The central values of the data points for the electron and muon modes are shifted horizontally for better readability.

Figure 3

$Q_4$ and $Q_5$ observables with SM and favored NP “Scenario 1" from Ref. [9].