Analysis of J/psi pi+ pi- and D0 D0-bar pi0 Decays of the X(3872)

TL;DR

This paper analyzes decay data of the X(3872) resonance, revealing its nature as a weakly-bound charm meson molecule by carefully considering the universal features of an S-wave threshold resonance and the effects of energy prescription choices.

Contribution

It provides a detailed analysis of X(3872) decay channels accounting for threshold resonance effects, leading to a refined mass measurement below the D*0 D0-bar threshold.

Findings

X(3872) mass is below the D*0 D0-bar threshold

The resonance is consistent with a weakly-bound charm meson molecule

Analysis accounts for non-integrable line shapes and energy prescription effects

Abstract

We analyze recent data from the Babar and Belle Collaborations on the X(3872) resonance in the J/psi pi+ pi- and D0 D0-bar pi0 decay channels, taking careful account of the universal features of an S-wave threshold resonance. Because the line shapes for such a resonance are not integrable functions of the energy, the resonance parameters depend on the prescriptions used to define them. In recent experimental analyses of the D0 D0-bar pi0 channel, an event near the D*0 D0-bar threshold was assumed to come from D*0 D0-bar or D0 D0*-bar and was therefore assigned an energy above the threshold. Taking this effect into account, our analysis of the D0 D0-bar pi0 data gives a mass for the X(3872) that is below the D*0 D^0-bar threshold. Our analyses in both the J/psi pi+ pi- and D0 D0-bar pi0 channels are consistent with the identification of the X(3872) as an extremely weakly-bound charm meson molecule.