Abstract
Angular correlations in $B^+\to X(3872) K^+$ decays, with $X(3872)\to \rho^0 J/\psi$, $\rho^0\to\pi^+\pi^-$ and $J/\psi \to\mu^+\mu^-$, are used to measure orbital angular momentum contributions and to determine the $J^{PC}$ value of the $X(3872)$ meson. The data correspond to an integrated luminosity of 3.0 fb$^{-1}$ of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be $J^{PC}=1^{++}$. The $X(3872)$ is found to decay predominantly through S wave and an upper limit of $4\%$ at $95\%$ C.L. is set on the fraction of D wave.
Highlights
The Xð3872Þ state was discovered in Bþ;0 → Xð3872ÞKþ;0, Xð3872Þ → πþπ−J=ψ, J=ψ → lþl− decays by the Belle experiment [1] and subsequently confirmed by other experiments [2,3,4].1 Its production was studied at the LHC [5,6]
Using 1.0 fb−1 of pp collision data collected by LHCb, JPC 1⁄4 2−þ was ruled out in favor of the 1þþ assignment, using the angular correlations in the same decay chain, with the Xð3872Þ state produced in Bþ → Xð3872ÞKþ decays [17]
Both angular analyses assumed that the lowest orbital angular momentum between the Xð3872Þ decay products (Lmin) dominated the matrix element
Summary
Quantum numbers of the Xð3872Þ state and orbital angular momentum in its ρ0J=ψ decay. The data correspond to an integrated luminosity of 3.0 fb−1 of proton-proton collisions collected with the LHCb detector This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be JPC 1⁄4 1þþ. Using 1.0 fb−1 of pp collision data collected by LHCb, JPC 1⁄4 2−þ was ruled out in favor of the 1þþ assignment, using the angular correlations in the same decay chain, with the Xð3872Þ state produced in Bþ → Xð3872ÞKþ decays [17]. Both angular analyses assumed that the lowest orbital angular momentum between the Xð3872Þ decay products (Lmin) dominated the matrix element.
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