First evidence reported for X(3872)→π⁰χ_c0 decay at 3.4σ, with branching fraction ratio 2.3 relative to π⁺π⁻J/ψ, upper limits on other modes, and no signal for X(3915)→π⁰χ_c1.
Determination of the X(3872) meson quantum numbers
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abstract
The quantum numbers of the X(3872) meson are determined to be JPC = 1++ based on angular correlations in B+ to X(3872) K+ decays, where X(3872) to pi+pi- J/psi and J/psi to \mu+\mu-. The data correspond to 1.0 fb-1 of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements, JPC=2-+, is rejected with a confidence level equivalent to more than eight Gaussian standard deviations using the likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X(3872) state.
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First observation of χ_c1(3872) → J/ψ μ⁺μ⁻ reported at 6.5σ significance with branching fraction ratio (1.68 ± 0.37) × 10^{-3} relative to the π⁺π⁻ mode.
Heavy-quark large-mass limit applied to E1 transitions of χ_c1(2P) yields decay rates that match LHCb measurements for χ_c1(3872) under the 2P assignment.
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