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Evidence of $CP$ violation in $B^+\to p\bar{p}K^+$ decays

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Abstract

Three-body $B^+\to p \overline p K^+$ and $B^+\to p \overline p \pi^+$ decays are studied using a data sample corresponding to an integrated luminosity of 3.0 $fb^{-1}$ collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$ and $8$ TeV. Evidence of CP violation in the $B^+\to p \overline p K^+$ decay is found in regions of the phase space, representing the first measurement of this kind for a final state containing baryons. Measurements of the forward-backward asymmetry of the light meson in the $p\overline p$ rest frame yield $A_{\mathrm{FB}}(p \overline p K^+, m_{p\overline p}<2.85\mathrm{ Ge V /}c^2)=0.495\pm0.012 (\mathrm{stat})\pm0.007 (\mathrm{syst})$ and $A_{\mathrm{FB}}(p\overline p \pi^+, m_{p\overline p}<2.85\mathrm{ Ge V /}c^2)=-0.409\pm0.033 (\mathrm{stat})\pm0.006 (\mathrm{syst})$. In addition, the branching fraction of the decay $B^+\to\overline{\Lambda}(1520)p$ is measured to be $\mathcal{B}(B^+ \to \overline{\Lambda}(1520)p)=(3.15\pm0.48 (\mathrm{stat})\pm0.07 (\mathrm{syst})\pm0.26 (\mathrm{BF}))\times 10^{-7}$, where BF denotes the uncertainty on secondary branching fractions.

Figures and captions

Invariant mass distributions of (left) $p\overline p K ^+ $ and (right) $p\overline p \pi ^+ $ candidates. The points with error bars represent data. The solid black line represents the total fit function. The components are represented by blue dashed (signal), purple dotted (cross-feed), red long-dashed (combinatorial background) and green dashed-dotted (partially reconstructed background) curves.

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Background-subtracted and acceptance-corrected Dalitz-plot distributions for (left) $ B^+ \rightarrow p \overline p K ^+ $ and (right) $ B^+ \rightarrow p \overline p \pi ^+ $ .

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Background-subtracted and acceptance-corrected normalized distributions of $\cos\theta_p$ for $ B^+ \rightarrow p \overline p K ^+ $ and $ B^+ \rightarrow p \overline p \pi ^+ $ decays, for $m_{p\overline p }<2.85 {\mathrm{ Ge V /}c^2} $. The data points are shown with their total uncertainties.

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Forward-backward asymmetry in bins of $m_{p\overline p }$ for $ B^+ \rightarrow p \overline p K ^+ $ and $ B^+ \rightarrow p \overline p \pi ^+ $ decays. The data points are shown with their total uncertainties.

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Asymmetries of the number of signal events in bins of the Dalitz-plot variables for $ B ^\pm \rightarrow p \overline p K^{\pm}$ . The number of events in each bin is approximately 300.

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$N(B^-)-N(B^+)$ in bins of $m_{p\overline p }^2$ for $m_{Kp}^2<10 {\mathrm{ Ge V^2 /}c^4} $ (black filled circles) and $m_{Kp}^2>10 {\mathrm{ Ge V^2 /}c^4} $ (open triangles).

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Animated gif made out of all figures.

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Tables and captions

Event yields and selection efficiency for $ B^+ \rightarrow p \overline p K ^+ $ and $ B^+ \rightarrow p \overline p \pi ^+ $ final states.

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$ C P$ asymmetries for $ B ^\pm \rightarrow p \overline p K^{\pm}$ and $ B ^\pm \rightarrow p \overline p \pi^{\pm}$ decays. The systematic uncertainties are dominated by the precision on the measurement $ A_{ C P } ( B ^\pm \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^\pm )$.

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Supplementary Material [file]

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Created on 17 August 2019.Citation count from INSPIRE on 20 August 2019.