On the nature of the X(3872) from QCD

Understand

We have studied some possible four-quark and molecule contents of the X(3872) using double ratios of sum rules, which are more accurate than the usual simple ratios often used in the literature for getting the hadron masses.

• We found that the different structures (\bar 3-3 and \bar 6-6 tetraquarks and D-D^{(*)} molecule) lead to the same prediction for the mass (within the accuracy of the method), indicating that the alone prediction of the X mass may not be sufficient to reveal its nature.
• In doing these analyses, we also find that (within our approximation) the use of the \bar{MS} running {\bar m}_c(m_c^2), rather than the on-shell mass, is more appropriate to obtain the J/\psi and X meson masses.
• Using vertex sum rules to roughly estimate the X(3872) hadronic and radiative widths, we found that the available experimental data does not exclude a \lambda-J/\psi-like molecule current.