In-medium hadron modification and meson spectroscopy

The theory of the strong interaction, Quantum Chromodynamics (QCD), has been remarkably successful in describing high-energy and short-distance-scale experiments involving quarks and gluons. However, applying QCD to low energy and large-distance-scale experiments has been a major challenge. At low energies, standard nuclear physics with nucleon and meson degrees of freedom work effectively in describing observations. The transition between the two descriptions of hadrons is one of the main goals of hadronic physics. Lattice QCD calculations have made tremendous progress and will one day give us a full description of strong interactions under all regimes. Meanwhile, effective theories incorporating some of the main features of QCD have been successfully developed and help us gain insight into the non-perturbative regime of QCD. All these models predict modifications of the properties of hadrons embedded in nuclear matter. Mesons with exotic quantum numbers are predicted at excitation energies below 2 GeV. Several experiments have been conducted with the Cebaf Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Laboratory (JLab) to test these predictions.