# 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 $0.05 < q^{2} < 22.00\mathrm{ Ge V} ^{2}/c^{4}$. 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. mass_Kmumu.pdf [33 KiB] HiDef png [195 KiB] Thumbnail [183 KiB] *.C file 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. cWidth.pdf [22 KiB] HiDef png [166 KiB] Thumbnail [127 KiB] *.C file 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. cAFBzoom.pdf [14 KiB] HiDef png [71 KiB] Thumbnail [42 KiB] *.C file cFHzoom.pdf [17 KiB] HiDef png [129 KiB] Thumbnail [107 KiB] *.C file Animated gif made out of all figures. PAPER-2012-024.gif Thumbnail

## 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 $1 < q^2 < 6\mathrm{ Ge V} ^{2}/c^{4}$ range where theoretical uncertainties are best under control. Table_1.pdf [53 KiB] HiDef png [99 KiB] Thumbnail [46 KiB] tex code

## Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [150 KiB] Supplementary information for LHCb-PAPER-2012-024. This archive contains: supplementary.pdf Fig1-supp.{pdf,png,eps} Fig2-supp.{pdf,png,eps} The figures are described in supplementary.pdf. Fig1-supp.pdf [24 KiB] HiDef png [219 KiB] Thumbnail [167 KiB] *C file Fig2-supp.pdf [15 KiB] HiDef png [102 KiB] Thumbnail [98 KiB] *C file

Created on 06 March 2021.