The role of the pion in the lineshape of the $X(3872)$

Abstract

We determine the contribution of long-range pion interactions to the $X(3872)$ dynamics, assuming it is a loosely bound $D^0{\bar{D}}^{\ast 0}$ molecule. Our result is based on the distorted wave Born approximation in non-relativistic quantum mechanics. Despite their long-range nature, we find that pion interactions cannot produce a large and negative effective range. Nonetheless, they introduce imaginary parts. In particular, they contribute to the total decay width of the $X(3872)$ with a term associated with, but not precisely corresponding to, the $D^{\ast }$ width. Our approach can also be applied to the recently discovered $T_{cc}^{+}$ states.

Comments: 9 pages, 1 figure. v2: minor changes. Comparison with ref. [26] improved