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

LHCb Collaboration; Bernet, R; Müller, K; Serra, N; Steinkamp, O; Straumann, U; Vollhardt, A; et al (2017). Observation of the annihilation decay mode $B^0 \to K^+K^-$. Physical Review Letters, 118(8):081801.

## 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 1.0 and 2.0  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 5 standard deviations. The analysis also results in an improved measurement of the branching fraction for the $B^0_s \to \pi^+\pi^-$ decay. The measured branching fractions are $\mathscr{B}(B^0 \to K^+K^−) = (7.80 \pm 1.27 \pm 0.81 \pm 0.21) \times 10^{−8}$ and $\mathscr{B}(B^0_s \to \pi^+π^-) = (6.91 \pm 0.54 \pm 0.63 \pm 0.19 \pm 0.40) \times 10^{−7}$. 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 $B^0_s$ mode, the fourth accounts for the uncertainty on the ratio of the probabilities for b quarks to hadronize into $B^0_s$ and $B^0$ mesons.

## 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 1.0 and 2.0  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 5 standard deviations. The analysis also results in an improved measurement of the branching fraction for the $B^0_s \to \pi^+\pi^-$ decay. The measured branching fractions are $\mathscr{B}(B^0 \to K^+K^−) = (7.80 \pm 1.27 \pm 0.81 \pm 0.21) \times 10^{−8}$ and $\mathscr{B}(B^0_s \to \pi^+π^-) = (6.91 \pm 0.54 \pm 0.63 \pm 0.19 \pm 0.40) \times 10^{−7}$. 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 $B^0_s$ mode, the fourth accounts for the uncertainty on the ratio of the probabilities for b quarks to hadronize into $B^0_s$ and $B^0$ mesons.

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