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Measurement of the charge asymmetry in $B^{\pm}\rightarrow \phi K^{\pm}$ and search for $B^{\pm}\rightarrow \phi \pi^{\pm}$ decays

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Abstract

The \CP-violating charge asymmetry in $B^{\pm}\rightarrow \phi K^{\pm}$ decays is measured in a sample of $pp$ collisions at 7 TeV centre-of-mass energy, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ collected by the LHCb experiment. The result is $\mathcal{A}_{CP}(B^{\pm}\rightarrow \phi K^{\pm}) = \rm 0.022\pm 0.021 \pm 0.009$, where the first uncertainty is statistical and the second systematic. In addition, a search for the $B^{\pm}\rightarrow \phi \pi^{\pm}$ decay mode is performed, using the $B^{\pm}\rightarrow \phi K^{\pm}$ decay rate for normalization. An upper limit on the branching fraction $\mathcal{B}(B^{\pm}\rightarrow \phi \pi^{\pm})< 1.5\times 10^{-7}$ is set at 90% confidence level.

Figures and captions

Lowest-order Feynman diagrams of the Standard Model for the decays $ B ^+ \!\rightarrow \phi K ^+ $ (top) and $ B ^+ \!\rightarrow \phi\pi ^+ $ (bottom). The diagrams with an external $\phi$ meson are OZI suppressed.

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BPHIPI.pdf [153 KiB]
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Distributions of the (a) $ K ^+ K ^- K ^- $ and (b) $ K ^+ K ^- $ masses of the selected $ B ^- \!\rightarrow \phi K ^- $ candidates, as well as of the (c) $ K ^+ K ^- K ^+ $ and (d) $ K ^+ K ^- $ masses of the selected $ B ^+ \!\rightarrow \phi K ^+ $ candidates. The solid blue curves represent the result of the simultaneous fit described in the text, with the following components: $ B ^\pm \!\rightarrow \phi K ^\pm $ signal (dotted red), nonresonant $ B ^\pm \!\rightarrow K ^+ K ^- K ^\pm $ background (dashed red), partially-reconstructed $b$-hadron background with (dotted blue) or without (dashed blue) a true $\phi$ meson, and combinatorial background with (dotted green) or without (dashed green) a true $\phi$ meson. Some of the components are barely visible because the corresponding yields are small. Normalized residuals are displayed below each histogram.

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BMass_Asymm_neg.pdf
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Distributions of the (a, c) $ K ^+ K ^- \pi ^\pm $ and (b, d) $ K ^+ K ^- $ masses of the selected $ B ^\pm \!\rightarrow \phi\pi ^\pm $ candidates, shown both with linear and logarithmic scales. The solid blue curves represent the result of the simultaneous fit described in the text, with the following components: $ B ^\pm \!\rightarrow \phi\pi ^\pm $ signal (dotted black), nonresonant $ B ^\pm \!\rightarrow K ^+ K ^- \pi ^\pm $ background (dashed black), $ B ^\pm \!\rightarrow \phi K ^\pm $ signal (dotted red), nonresonant $ B ^\pm \!\rightarrow K ^+ K ^- K ^\pm $ background (dashed red), partially-reconstructed $b$-hadron background with (dotted blue) or without (dashed blue) a true $\phi$ meson, and combinatorial background with (dotted green) or without (dashed green) a true $\phi$ meson. Normalized residuals are displayed below the histograms.

BMassP[..].pdf [39 KiB]
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BMassPi_PHIPI_Linear_Pad_cut.pdf
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PhiMassPi_PHIPI_Linear_Pad_cut.pdf
BMassP[..].pdf [23 KiB]
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BMassPi_PHIPI_Log.pdf
PhiMas[..].pdf [25 KiB]
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PhiMassPi_PHIPI_Log.pdf

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Tables and captions

Raw charge asymmetries for the $ B ^\pm \!\rightarrow \phi K ^\pm $ and $ B ^\pm \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^\pm $ decays, their difference $\Delta \mathcal{A}_{C\!P}$, and the fraction of $ B ^\pm \!\rightarrow \phi K ^\pm $ signal events in each trigger subsample for $k = \rm TOS, TIS$. All uncertainties are statistical only.

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Systematic uncertainties on the measurement of $\Delta\mathcal{A}_{C\!P}$.

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Supplementary Material [file]

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