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Observation of the annihilation decay mode $B^{0}\to K^{+}K^{-}$

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Abstract

A search for the $B^{0}\to K^{+}K^{-}$ decay is performed using $pp$-collision data collected by LHCb. The data set corresponds to integrated luminosities of 1 and 2 fb$^{-1}$ at center-of-mass energies of 7 and 8 TeV, respectively. This decay is observed for the first time, with a significance of more than five standard deviations. The analysis also results in an improved measurement of the branching fraction for the $B_s^0\to \pi^+\pi^-$ decay. The measured branching fractions are $BR(B^0\to K^+K^-) = (7.80 \pm 1.27 \pm 0.81 \pm 0.21) \times 10^{-8}$ and $BR(B_s^0\to\pi^+\pi^-) = (6.91 \pm 0.54 \pm 0.63 \pm 0.19 \pm 0.40) \times 10^{-7}$. The first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the $B^0\to K^+\pi^-$ branching fraction used as a normalization. For the $B_s^0$ mode, the fourth accounts for the uncertainty on the ratio of the probabilities for $b$ quarks to hadronize into $B_s^0$ and $B^0$ mesons.

Figures and captions

Dominant Feynman graphs contributing to the $ B ^0 \!\rightarrow K ^+ K ^- $ and $ B ^0_ s \!\rightarrow \pi ^+ \pi ^- $ decay amplitudes: (left) penguin-annihilation and (right) $W$-exchange topologies.

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Distributions of (left) $m_{ K ^+ K ^- }$ and (right) $m_{\pi ^+ \pi ^- }$ for candidates passing $S_{ K ^+ K ^- }$ and $S_{\pi ^+ \pi ^- }$, respectively. The continuous (blue) curves represent the results of the best fits to the data points. The most relevant contributions to the invariant mass spectra are shown as indicated in the legends. The vertical scales are chosen to magnify the relevant signal regions. The bin-by-bin differences between the fits and the data, in units of standard deviations, are also shown.

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Log-likelihood ratio as a function of the $ B ^0 \!\rightarrow K ^+ K ^- $ signal yield. The dashed (red) and continuous (blue) curves correspond to the exclusion and to the inclusion of systematic uncertainties, respectively.

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Animated gif made out of all figures.

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Tables and captions

Systematic uncertainties on the yields for the $ B ^0 \!\rightarrow K ^+ K ^- $ and $ B ^0_ s \!\rightarrow \pi ^+ \pi ^- $ decays.

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Supplementary Material [file]

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2016-036. The files are: Supplementary.pdf : An overview of the extra figures and tables *.pdf, *.png, *.eps *.C : The figures in variuous formats

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Created on 11 December 2018.Citation count from INSPIRE on 11 December 2018.