# Measurement of the isospin asymmetry in $B \to K^{(*)}\mu^+\mu^-$ decays

Abstract : The isospin asymmetries of $B \to K^{(*)}\mu^+\mu^-$ decays and the partial branching fractions of $B^0 \to K^0\mu^+\mu^-$ and $B^+ \to K^{*+}\mu^+\mu^-$ are measured as a function of the di-muon mass squared $q^2$ using an integrated luminosity of 1.0 fb$^{-1}$ collected with the LHCb detector. The $B \to K\mu^+\mu^-$ isospin asymmetry integrated over $q^2$ is negative, deviating from zero with over 4 $\sigma$ significance. The $B \to K^{*}\mu^+\mu^-$ decay measurements are consistent with the Standard Model prediction of negligible isospin asymmetry. The observation of the decay $B^0 \to K^0_{\rm\scriptscriptstyle S}\mu^+\mu^-$ is reported with 5.7 $\sigma$ significance. Assuming that the branching fraction of $B^0 \to K^0\mu^+\mu^-$ is twice that of $B^0 \to K^0_{\rm\scriptscriptstyle S}\mu^+\mu^-$, the branching fractions of $B^0 \to K^0\mu^+\mu^-$ and $B \to K^{*+}\mu^+\mu^-$ are found to be ($0.31^{+0.07}_{-0.06}) \times 10^{-6}$ and ($1.16\pm0.19) \times 10^{-6}$, respectively.
Document type :
Journal articles

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Submitted on : Wednesday, May 16, 2012 - 2:02:56 PM
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### Citation

R. Aaij, S. Barsuk, O. Callot, J. He, B. Jean-Marie, et al.. Measurement of the isospin asymmetry in $B \to K^{(*)}\mu^+\mu^-$ decays. Journal of High Energy Physics, Springer, 2012, 07, pp.133. ⟨10.1007/JHEP07(2012)133⟩. ⟨in2p3-00698159⟩

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