First observation of [¯ over B][superscript 0] → J/ψK[superscript +]K[superscript -] and search for [¯ over B][superscript 0] → J/ψϕ decays

Abstract

The first observation of the [¯ over B][superscript 0] → J/ψK[superscript +]K[superscript −] decay is presented with a data sample corresponding to an integrated luminosity of 1.0 fb[superscript −1] of pp collisions at a center-of-mass energy of 7 TeV collected with the LHCb detector. The branching fraction is measured to be B([¯ over B][superscript 0 → J/ψK[superscript +]K[superscript −]) = (2.53 ± 0.31 ± 0.19) × 10[superscript −6], where the first uncertainty is statistical and the second is systematic. An amplitude analysis of the final state in the [¯ over B][superscript 0] → J/ψK[superscript +]K[superscript −] decay is performed to separate resonant and nonresonant contributions in the K[superscript +]K[superscript −] spectrum. Evidence of the a[subscript 0](980) resonance is reported with statistical significance of 3.9 standard deviations. The corresponding product branching fraction is measured to be B([¯ over B][superscript 0] → J/ψa[subscript 0](980), a[subscript 0](980) → K[superscript +]K[superscript −]) = (4.70 ± 3.31 ± 0.72) × 10[superscript −7], yielding an upper limit of B([¯ over B][superscript 0] → J/ψa[subscript 0](980), a[subscript 0](980) → K[superscript +]K[superscript −]) < 9.0 × 10[superscript −7] at 90% confidence level. No evidence of the resonant decay [¯ over B][superscript 0] → J/ψϕ is found, and an upper limit on its branching fraction is set to be B([¯ over B][superscript 0] → J/ψϕ) < 1.9 × 10[superscript −7] at 90% confidence level.