Nature of X(3872) from its radiative decay

Abstract

We study the radiative decay of X(3872) based on the assumption that X(3872) is regarded as a cc‾ charmonium with quantum number JPC=1++ (J,P,C represent the spin, parity and charge conjugation, respectively). The form factors of X(3872) transitions to J/ψγ and ψ′γ (ψ′ denotes ψ(2S) throughout the paper) are calculated in the framework of the covariant light-front quark model. The phenomenological wave function of a meson depends on the parameter β, whose inverse essentially describes the confinement scale. In the present work, the parameters β for the vector J/ψ and ψ′ mesons will be determined through their decay constants, which are obtained from the experimental values of their partial decay widths to the electron-positron pair. For X(3872), we determined the value of β by the decay width of X(3872)→ψ′γ. Then, we examined the width of X(3872)→J/ψγ in a manner of parameter-free prediction and compared it with the experimental value. As a result, an inconsistency or contradiction occurs between the widths of X(3872)→J/ψγ and X(3872)→ψ′γ. We thus conclude that X(3872) cannot be a pure cc‾ resonance and that other components are necessary in its wave function.