Is X(3872) a bound state?

Abstract

All existing experimental evidence for the bound state nature of X(3872) relies on observing its decay products, which are measured with a finite experimental mass resolution that is typically deltam>2 MeV , and much larger than its alleged binding energy, Bx = 0.00(18) MeV. On the other hand, we have found recently that there is a clear cancellation in the 1++ channel of the invariant DD* mass around the threshold between continuum and the bound state. This is very much like a similar cancellation in the proton-neutron continuum with the deuteron in the 1++ channel. Based on comparative fits with a common Tsallis distribution of the experimental cross-sections for prompt production of deuterons and X(3872) in pp collisions with a finite Pt , we find a strong argument for questioning the bound state nature of this state, which also suggests that the large observed production rate could be consistent with a half-bound state.