The nature of the X(3872) enhancement is analysed in the framework of the Resonance-Spectrum Expansion, by studying it as a regular $J^{ PC}=1^{ ++}$ charmonium state, though strongly influenced and shifted by open-charm decay channels. The observed but Okubo-Zweig-Iizuka-forbidden $\rho^0 J/\psi$ and $\omega J/\psi$ channels are coupled as well, but effectively smeared out by using complex $\rho^0$ and $\omega$ masses, in order to account for their physical widths, followed by a rigorous algebraic procedure to restore unitarity. A very delicate interplay between the $D^0 D^{ *0}$, $\rho^0 J/\psi$, and $\omega J/\psi$ channels is observed. The data clearly suggest that the X(3872) is a very narrow axial-vector $c\bar{ c}$ resonance, with a pole at or slightly below the $D^0D^{ *0}$ threshold.
Categories: hep-ph hep-ex math-ph math.MP