Adjoint hadrons reveal the pattern of exotic hidden-heavy hadrons
An overarching explanation of exotic hadrons containing a heavy quark-antiquark pair has eluded the theoretical physics community for more than two decades. A recent study by Eric Braaten (OSU, co-PI) and Roberto Bruschini (OSU, ExoHad postdoc) points out that the pattern of these exotic hidden-heavy hadrons is largely determined by the spectrum of adjoint hadrons, which are the energy levels of quarks and gluons bound to a static color-octet source. The study explains exotic hidden-heavy hadrons as bound states and resonances in potentials defined by the energy levels of QCD with two static color sources separated by a variable distance. Each potential connects a repulsive adjoint-hadron potential at short distances to a constant hadron-pair potential at long distances.
To support exotic hidden-heavy hadrons, such a potential must have a minimum at intermediate distances, where it describes a compact multiquark configuration. As an application of this pattern, the study uses existing data on the hidden-heavy tetraquarks to constrain the low-energy spectrum of adjoint mesons. A subsequent study by the same authors, in collaboration with Fareed Alasiri (OSU, ExoHad student), uses the expected low-energy spectrum of adjoint baryons to predict the quantum numbers, masses, and decay widths of hidden-heavy pentaquarks.
This unified picture of the exotic hidden-heavy hadrons indicates that a solution to this longstanding puzzle might be finally within reach.