# Production of $X(3872)$ Accompanied by a Soft Pion at Hadron Colliders

## TL;DR

This paper explores the production mechanisms of the exotic state $X(3872)$ with a soft pion at hadron colliders, proposing that a narrow peak near the $D^* ar D^*$ threshold could be observed at the LHC due to charm-meson rescattering effects.

## Contribution

It introduces a novel production mechanism involving charm-meson rescattering leading to a detectable peak in the $X o X ext{ and } ext{pion}$ invariant mass distribution at hadron colliders.

## Key findings

- A narrow peak near the $D^* ar D^*$ threshold can appear in the $X ext{ and } ext{pion}$ invariant mass distribution.
- The peak's cross section ratio suggests it could be observable at the LHC.
- The mechanism involves charm-meson triangle singularity effects.

## Abstract

If the $X(3872)$ is a weakly bound charm-meson molecule, it can be produced by the creation of $D^{*0} \bar{D}^0$ or $D^{0} \bar{D}^{*0}$ at short distances followed by the formation of the bound state from the charm-meson pair. The $X$ can also be produced by the creation of $D^* \bar{D}^*$ at short distances followed by the rescattering of the charm-meson pair into $X \pi$. At a high-energy hadron collider, the prompt cross section from this mechanism has a narrow peak in the $X \pi$ invariant mass distribution near the $D^* \bar D^*$ threshold from a charm-meson triangle singularity. An order-of-magnitude estimate of the ratio of the cross section for producing the peak in the $X \pi^\pm$ distribution to the cross section for producing $X$ without an accompanying pion suggests that the peak may be observable at the LHC.