# Observation of a resonance in B+→K+μ+μ− decays at low recoil

LHCb Collaboration; et al; Bernet, R; Müller, K; Steinkamp, O; Straumann, U; Vollhardt, A (2013). Observation of a resonance in B+→K+μ+μ− decays at low recoil. Physical Review Letters, 111:112003.

## Abstract

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+9−8  MeV/c2 and 65+22−16  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.

## Abstract

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+9−8  MeV/c2 and 65+22−16  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.

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