000003237 001__ 3237
000003237 005__ 20220920011800.0
000003237 037__ $$aBELLE2-CONF-PH-2022-009
000003237 041__ $$aeng
000003237 100__ $$aSeema Choudhury
000003237 245__ $$aMeasurement of the branching fraction for the decay $B \to K^{\ast}(892)\ell^+\ell^-$ at Belle II
000003237 260__ $$a$$c2022-09-20
000003237 300__ $$a11
000003237 520__ $$aWe report a measurement of the branching fraction of $B \to K^{\ast}(892)\ell^+\ell^-$ decays, where $\ell^+\ell^- = \mu^+\mu^-$ or $e^+e^-$, using electron-positron collisions recorded at an energy at or near the $\Upsilon(4S)$ mass and corresponding to an integrated luminosity of $189$ fb$^{-1}$. The data was collected during 2019--2021 by the Belle II experiment at the SuperKEKB $e^{+}e^{-}$ asymmetric-energy collider. We reconstruct $K^{\ast}(892)$ candidates in the $K^+\pi^-$, $K_{S}^{0}\pi^+$, and $K^+\pi^0$ final states. The signal yields with statistical uncertainties are $22\pm 6$, $18 \pm 6$, and $38 \pm 9$ for the decays $B \to K^{\ast}(892)\mu^+\mu^-$, $B \to K^{\ast}(892)e^+e^-$, and $B \to K^{\ast}(892)\ell^+\ell^-$, respectively. We measure the branching fractions of these decays for the entire range of the dilepton mass, excluding the very low mass region to suppress the $B \to K^{\ast}(892)\gamma(\to e^+e^-)$ background and regions compatible with decays of charmonium resonances, to be \begin{align*}     {\cal B}(B \to K^{\ast}(892)\mu^+\mu^-) &= (1.19 \pm 0.31 ^{+0.08}_{-0.07}) \times 10^{-6},\\     {\cal B}(B \to K^{\ast}(892)e^+e^-) &= (1.42 \pm 0.48 \pm 0.09)\times 10^{-6}, \\     {\cal B}(B \to K^{\ast}(892)\ell^+\ell^-) &= (1.25 \pm 0.30  ^{+0.08}_{-0.07}) \times 10^{-6}, \end{align*} where the first and second uncertainties are statistical and systematic, respectively. These results, limited by sample size, are the first measurements of $B \to K^{\ast}(892)\ell^+\ell^-$ branching fractions from the Belle II experiment. 
000003237 6531_ $$arare decays
000003237 6531_ $$aBelle II
000003237 6531_ $$aEWP
000003237 6531_ $$ab->sll
000003237 6531_ $$aFCNC
000003237 6531_ $$aBR
000003237 6531_ $$aLFU 
000003237 8560_ $$fseema.choudhury@kek.jp
000003237 8564_ $$uhttps://docs.belle2.org/record/3237/files/BELLE2-CONF-PH-2022-009.pdf