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Differential branching fraction and angular analysis of the $B^+ \to K^+ \mu^+ \mu^-$ decay

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Abstract

The angular distribution and differential branching fraction of the decay $B^{+} \rightarrow K^{+}\mu^{+}\mu^{-}$ are studied with a dataset corresponding to $1.0\,\mathrm{fb}^{-1}$ of integrated luminosity, collected by the LHCb experiment. The angular distribution is measured in bins of dimuon invariant mass squared and found to be consistent with Standard Model expectations. Integrating the differential branching fraction over the full dimuon invariant mass range yields a total branching fraction of $\mathcal{B}(B^{+} \rightarrow K^{+}\mu^{+}\mu^{-}) = (4.36 \pm 0.15 \pm 0.18)\times 10^{-7}$. These measurements are the most precise to date of the $B^{+} \rightarrow K^{+}\mu^{+}\mu^{-}$ decay.

Figures and captions

Invariant mass of selected $ B ^+ \!\rightarrow K ^+ \mu ^+\mu ^- $ candidates with $0.05 < q^{2} < 22.00\mathrm{\,GeV} ^{2}/c^{4}$. Candidates with a dimuon invariant mass consistent with that of the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ or $\psi {(2S)}$ are excluded. The peaking background contribution from the decays $ B ^+ \!\rightarrow K ^+ \pi ^+ \pi ^- $ and $ B ^+ \!\rightarrow \pi ^+ \mu ^+\mu ^- $ is indicated in the figure.

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Differential branching fraction of $ B ^+ \!\rightarrow K ^+ \mu ^+\mu ^- $ as a function of the dimuon invariant mass squared, $q^{2}$. The SM theory prediction (see text) is given as the continuous cyan (light) band and the rate-average of this prediction across the $q^{2}$ bin is indicated by the purple (dark) region. No SM prediction is included for the regions close to the narrow $ c \overline c $ resonances.

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Dimuon forward-backward asymmetry, $A_{\rm FB}$, and the parameter $F_{\rm H}$ for $ B ^+ \!\rightarrow K ^+ \mu ^+\mu ^- $ as a function of the dimuon invariant mass squared, $ q^2$ . The SM theory prediction (see text) for $F_{\rm H}$ is given as the continuous cyan (light) band and the rate-average of this prediction across the $ q^2$ bin is indicated by the purple (dark) region. No SM prediction is included for the regions close to the narrow $ c \overline c $ resonances.

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Tables and captions

Signal yield ($N_{\text{sig}}$), differential branching fraction ($\mathrm{d}\cal B /\mathrm{d} q^2 $), the parameter $F_{\rm H}$ and dimuon forward-backward asymmetry ($A_{\rm FB}$) for the $ B ^+ \!\rightarrow K ^+ \mu ^+\mu ^- $ decay in the $ q^2$ bins used in the analysis. Results are also given in the $1 < q^2 < 6\mathrm{\,GeV} ^{2}/c^{4}$ range where theoretical uncertainties are best under control.

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Supplementary Material [file]

Supplementary material full pdf

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Created on 22 February 2019.Citation count from INSPIRE on 22 February 2019.