Determination of the X(3872) Meson Quantum Numbers

The quantum numbers of the X ( 3872 ) meson are determined to be J P C = 1 ++ based on angular correlations in B + → X ( 3872 ) K + decays, where X ( 3872 ) → π + π − J / ψ and J / ψ → μ + μ − . The data correspond to 1.0 fb − 1 of p p collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements J P C = 2 − + is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X ( 3872 ) state.