A search for the rare decays B 0 s ! þ À and B 0 ! þ À is performed at the LHCb experiment. The data analyzed correspond to an integrated luminosity of 1 fb À1 of pp collisions at a center-of-mass energy of 7 TeV and 2 fb À1 at 8 TeV. An excess of B 0 s ! þ À signal candidates with respect to the background expectation is seen with a significance of 4.0 standard deviations. A time-integrated branching fraction of BðB 0 s ! þ À Þ ¼ ð2:9 þ1:1 À1:0 Þ Â 10 À9 is obtained and an upper limit of BðB 0 ! þ À Þ < 7:4 Â 10 À10 at 95% confidence level is set. These results are consistent with the standard model expectations.

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A broad peaking structure is observed in the dimuon spectrum of B+ → K+ μ+ μ- decays in the kinematic region where the kaon has a low recoil against the dimuon system. The structure is consistent with interference between the B+ → K+ μ+ μ- decay and a resonance and has a statistical significance exceeding six standard deviations. The mean and width of the resonance are measured to be 4191(-8)(+9)  MeV/c2 and 65(-16)(+22)  MeV/c2, respectively, where the uncertainties include statistical and systematic contributions. These measurements are compatible with the properties of the ψ(4160) meson. First observations of both the decay B+ → ψ(4160)K+ and the subsequent decay ψ(4160) → μ+ μ- are reported. The resonant decay and the interference contribution make up 20% of the yield for dimuon masses above 3770  MeV/c2. This contribution is larger than theoretical estimates.

Direct and mixing-induced CP -violating asymmetries in B 0 s → K + K − decays are measured for the first time using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0 fb −1 , collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The results are C KK = 0.14 ± 0.11 ± 0.03 and S KK = 0.30 ± 0.12 ± 0.04, where the first uncertainties are statistical and the second systematic. The corresponding quantities are also determined for B 0 → π + π − decays to be C ππ = −0.38 ± 0.15 ± 0.02 and S ππ = −0.71 ± 0.13 ± 0.02, in good agreement with existing measurements.

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