Abstract |
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We present measurements of the flavor-changing neutral current
decays $B\to K\ell^+\ell^-$ and $B\to K^*\ell^+\ell^-$,
where $\ell^+\ell^-$ is either an $e^+e^-$ or $\mu^+\mu^-$ pair.
The data sample comprises $229\times 10^6$
$Y(4S) \rightarrow B\overline{B}$
decays collected with the BaBar detector at the PEP-II $e^+e^-$ storage ring.
Flavor-changing neutral current decays are highly suppressed in the Standard
Model and their predicted properties could be significantly modified
by new physics at the electroweak scale.
We measure the branching fractions
${\cal B}(B \rightarrow K\ell\ell) = (0.34\pm 0.07 \pm 0.02)
\times 10^{-6}$,
${\cal B}(B \rightarrow K^{*}\ell\ell) = (0.78^{+0.19}_{-0.17}\pm 0.11) \times 10^{-6}$,
the direct $CP$ asymmetries of these decays, and the relative abundances
of decays to electrons and muons. For two regions in $\ell^+\ell^-$
mass, above and below $m_{J/\psi}$, we measure partial branching fractions
and the forward-backward angular asymmetry of the lepton pair. In these
same regions we also measure the $K^*$
longitudinal polarization in $B \rightarrow K^*\ell^+\ell^-$ decays.
Upper limits are obtained for the
lepton flavor-violating decays
$B\rightarrow Ke\mu$ and $B\rightarrow K^{*}e\mu$.
All measurements are consistent with Standard Model expectations.
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