Abstract:
A many-body system that includes loosely bound molecules can be described by an effective field theory with a relevant interaction whose strength is proportional to the small inverse scattering length of the constituents. The “contact” for such a system is the thermodynamic variable conjugate to the large scattering length. In the dilute limit, the number density of loosely bound molecules is proportional to the contact. A central relativistic heavy-ion collision produces an expanding hadron gas in which charm mesons are in thermal equilibrium. As a consequence, the production rate of loosely bound charm-meson molecules, such as X(3872), can be determined from the contact at the time of the kinetic freezeout of charm mesons.
