  We describe the application of effective field theories for quantum
chromodynamics (QCD) to two bound states involving heavy quarks: the $T_{cc}^+$
exotic meson and the $J/\psi$. We study the decay of the $T_{cc}^+$ in an
effective theory for hadronic molecules, and find agreement with experiment. We
also use the nonrelativistic QCD (NRQCD) factorization formalism to derive the
leading-order transverse momentum dependent fragmentation functions (FFs) for
quarks and gluons fragmenting to $J/\psi$. We then make use of these TMD FFs to
compare the $J/\psi$ production mechanisms of light quark fragmentation and
photon-gluon fusion, where the conclusions we draw can motivate future
experiments at the Electron Ion Collider, shedding light on the inner structure
of nucleons and testing ideas from NRQCD factorization. These results showcase
the utility of effective field theories in explaining experiments and testing
key concepts in nuclear/particle physics.
