Heavy hadronic molecules with pion exchange and quark core couplings: a guide for practitioners

TL;DR

This paper explores the formation of heavy hadronic molecules near thresholds, emphasizing the roles of pion exchange and quark core couplings, with detailed analysis of interactions and channel effects.

Contribution

It provides a detailed framework for understanding hadronic molecules as mixtures of long-range hadron interactions and short-range quark structures, with practical insights for researchers.

Findings

Tensor force properties are crucial in pion exchange interactions.

More coupled channels increase attraction and molecule formation likelihood.

Heavier constituents reduce kinetic energy, favoring molecule stability.

Abstract

We discuss selected and important features of hadronic molecules as one of promising forms of exotic hadrons near thresholds. Using examples of $D \bar D^*$ systems such as $X(3872)$ and $Z_c$, emphasis is put on the roles of the one pion exchange interaction between them and their coupling to intrinsic quark states. Thus hadronic molecules emerge as admixtures of the dominant long-range hadron structure and short-range quark structure. For the pion exchange interaction, properties of the tensor force are analyzed in detail. More coupled channels supply more attractions, and heavier constituents suppress kinetic energies, providing more chances to form hadronic molecules of heavy hadrons. Throughout this article, we show details of basic ideas and methods.