Threshold Effects and the Line Shape of the X(3872) in Effective Field Theory

TL;DR

This paper develops an effective field theory to analyze the line shape and threshold effects of the X(3872) meson, aiding in accurately determining its pole position from experimental data.

Contribution

It introduces a new EFT framework considering Galilean invariance and pion interactions to study the X(3872)'s properties near threshold.

Findings

Derived relations between X(3872) mass, width, and line shape.

Provided a method to extract the pole position from near-threshold data.

Analyzed the impact of pion interactions on the X(3872) width.

Abstract

Latest measurements suggest that the X(3872) mass lies less than 200 keV away from the D0-Dbar0* threshold, reenforcing its interpretation as a loosely-bound mesonic molecule. This observation implies that in processes like D0-Dbar0-pi0 production, threshold effects could disguise the actual pole position of the X(3872). We propose a new effective field theory with D0, Dbar0 and pi0 degrees of freedom for the X(3872), considering Galilean invariance to be an exact symmetry. The D0* enters as a D0-pi0 p-wave resonance, allowing for a comprehensive study of the influence of pion interactions on the X(3872) width. We calculate relations between the mass of the X(3872), its width, and its line shape in D0-Dbar0-pi0 production up to next-to-leading order. Our results provide a tool for the extraction of the X(3872) pole position from the experimental data near threshold.