Radiative decays and the LHCb line-shape data are incompatible with a purely molecular X(3872) and favor a compact or partially composite state, with a proposed molecular-amplitude fit for a decisive test.
Galilean-Invariant XEFT at Next-to-Leading Order
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abstract
XEFT is a low-energy effective field theory for charm mesons and pions that provides a systematically improvable description of the $X(3872)$ resonance. To simplify calculations beyond leading order, we introduce a new formulation of XEFT with a dynamical field for a pair of charm mesons in the resonant channel. We simplify the renormalization of XEFT by introducing a new renormalization scheme that involves the subtraction of amplitudes at the complex $D^{*0} \bar D^0$ threshold. The new formulation and the new renormalization scheme are illustrated by calculating the complex pole energy of $X$ and the $D^{*0} \bar D^0$ scattering amplitude to next-to-leading order using Galilean-invariant XEFT.
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A short review on the compositeness of the $X(3872)$
Radiative decays and the LHCb line-shape data are incompatible with a purely molecular X(3872) and favor a compact or partially composite state, with a proposed molecular-amplitude fit for a decisive test.