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Studies of the decays $B^+ \to p \bar p h^+$ and observation of $B^+ \to \bar{\Lambda}(1520)p$

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Abstract

Dynamics and direct $C\P$ violation in three-body charmless decays of charged $B$ mesons to a proton, an antiproton and a light meson (pion or kaon) are studied using data, corresponding to an integrated luminosity of 1.0$ {\,fb}^{-1}$, collected by the ${LHCb}$ experiment in $pp$ collisions at a center-of-mass energy of 7 TeV. Production spectra are determined as a function of Dalitz-plot and helicity variables. The forward-backward asymmetry of the light meson in the $p\bar p$ rest frame is measured. No significant $C\P$ asymmetry in $B^+ \to p \bar p K^+$ decay is found in any region of the Dalitz plane. We present the first observation of the decay $B^+ \to \bar{\Lambda}(1520)(\to K^+\bar p)p$ near the $K^+\bar p$ threshold and measure $\mathcal{B}(B^+ \to \bar{\Lambda}(1520)p)=(3.9^{+1.0}_{-0.9} (\mathrm{stat})\pm0.1 (\mathrm{syst})\pm0.3 (\mathrm{BF}))\times 10^{-7}$, where BF denotes the uncertainty on secondary branching fractions.

Figures and captions

Leading tree and penguin diagrams for $ B^+ \rightarrow p \overline p h^+$ decays.

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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. Blue dashed, purple dotted, red long-dashed and green dashed-dotted curves represent the signal, cross-feed, combinatorial background and partially reconstructed background, respectively.

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Efficiency-corrected differential yield as a function of $m_{p\overline p }$ for (left) $ B^+ \rightarrow p \overline p K ^+ $ and (right) $ B^+ \rightarrow p \overline p \pi ^+ $ . The data points are shown with their statistical and total uncertainties. For comparison, the solid lines represent the expectations for a uniform phase space production, normalized to the efficiency-corrected area.

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Efficiency-corrected differential yield as a function of $m_{Kp}^2$ for $ B^+ \rightarrow p \overline p K ^+ $ . The data points are shown with their statistical and total uncertainties. The solid line represents the expectation for a uniform phase space production, normalized to the efficiency-corrected area, for comparison.

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Efficiency-corrected differential yields as functions of $\cos\theta_p$ for (left) $ B^+ \rightarrow p \overline p K ^+ $ and (right) $ B^+ \rightarrow p \overline p \pi ^+ $ modes, after subtraction of the charmonium contributions. The data points are shown with their statistical and total uncertainties.

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Signal weighted Dalitz-plot distributions for (left) $ B^+ \rightarrow p \overline p K ^+ $ and (right) $ B^+ \rightarrow p \overline p \pi ^+ $ . Also shown are the iso-$\cos\theta_p$ lines corresponding to the $\cos\theta_p$ bin boundaries; $\cos\theta_p=-1$ (+1) is the uppermost (lowermost) line. The distributions are not corrected for efficiency.

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Distribution of $ A_{\mathcal{C}_{P} }$ for the Dalitz-plot projections on $m_{p\overline p }$ and $m_{Kp}^2$ for $ B ^\pm \rightarrow p \overline p K^{\pm}$ events. In the $m_{p\overline p }$ projection (left), the bin $[2.85,3.15] {\mathrm{\,GeV\!/}c^2} $ contains only the value of the charmless $p\overline p K ^\pm $ after subtraction of the $\eta _ c $ - $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ contribution. The $m_{Kp}^2$ projection (right) has been obtained after removing the charmonia bands.

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Invariant mass $m_{Kp}$ for the $ B^+ \rightarrow p \overline p K ^+ $ candidates near threshold.

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Fit to the $B$ signal weighted $m_{Kp}$ distribution.

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Projections of (left) $m_{Kp}$ and (right) $m_{p\overline p K ^+ }$ of the two dimensional fit used to obtain the $ B^+ \rightarrow \overline{\Lambda} (1520)p$ signal yield.

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Animated gif made out of all figures.

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Tables and captions

Fitted $ B^+ \rightarrow p \overline p K ^+ $ signal yield, including the charmonium modes, efficiency and relative systematic uncertainty, in bins of $p\overline p $ invariant mass. The error on the efficiency includes all the sources of uncertainty.

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Fitted $ B^+ \rightarrow p \overline p \pi ^+ $ signal yield, including the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ mode, $ B^+ \rightarrow p \overline p K ^+ $ cross-feed yield, signal efficiency, and relative systematic uncertainty in bins of $p\overline p $ invariant mass.

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Yields, efficiencies and relative systematic uncertainties of the charmonium modes from the combined $(m_{p\overline p h^+},m_{p\overline p })$ fits for the regions $m_{p\overline p }\in[2.85,3.15] {\mathrm{\,GeV\!/}c^2} $ (for both $ B^+ \rightarrow p \overline p K ^+ $ and $ B^+ \rightarrow p \overline p \pi ^+ $ ) and $[3.60,3.75] {\mathrm{\,GeV\!/}c^2} $ (for $ B^+ \rightarrow p \overline p K ^+ $ ).

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Fitted $ B^+ \rightarrow p \overline p K ^+ $ yields after subtracting the charmonium bands, efficiencies and relative systematic uncertainties in bins of $Kp$ invariant mass squared.

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Fitted $ B^+ \rightarrow p \overline p K ^+ $ yields, efficiencies and relative systematic uncertainties in bins of $\cos\theta_{p}$.

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Fitted $ B^+ \rightarrow p \overline p \pi ^+ $ signal yields, efficiencies and relative systematic uncertainties in bins of $\cos\theta_{p}$.

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Systematic uncertainties for the $\mathcal{B}( B ^+ \rightarrow \overline{\Lambda} (1520)(\rightarrow K^+\overline p )p)/\mathcal{B}( B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\rightarrow p\overline p ) K ^+ )$ branching fraction ratio. The total uncertainty is the sum in quadrature of the individual sources.

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