Dynamics and direct $CP$ 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 $pbar p$ rest frame is measured. No significant $CP$ 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 $B^+ to kern 0.1embar{kern -0.1emLambda}(1520)(to K^+bar p)p$ near the $K^+bar p$ threshold and measure $mathcal{B}(B^+ to kern 0.1embar{kern -0.1emLambda}(1520)p)=(3.9^{+1.0}_{-0.9} (mathrm{stat})pm0.1 (mathrm{syst})pm0.3 (mathrm{BF}))times 10^{-7}$, where BF denotes the uncertainty on secondary branching fractions.
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