Evidence for CP violation in B+ →p p ¯ K+ decays

Three-body B+→pp¯K+ and B+→pp¯π+ decays are studied using a data sample corresponding to an integrated luminosity of 3.0fb-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+→pp¯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 pp¯ rest frame yield AFB(pp¯K+,mpp¯<2.85GeV/c2)=0.495±0.012(stat)±0.007(syst) and AFB(pp¯π+,mpp¯<2.85GeV/c2)=-0.409±0.033(stat)±0.006(syst). In addition, the branching fraction of the decay B+→Λ¯(1520)p is measured to be B(B+→Λ¯(1520)p)=(3.15±0.48(stat)±0.07(syst)±0.26(BF))×10-7, where BF denotes the uncertainty on secondary branching fractions.