Jozef Dudek
Jefferson Laboratory

Ryan Mitchell
Indiana University

Eric Swanson
University of Pittsburgh

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Kimberlee Choe
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INT Workshop INT-15-60W

Modern Exotic Hadrons

November 2-13, 2015


The recent high statistics confirmation of the Z(4430) by LHCb, and the startling demonstration of phase motion, has brought sharp focus on exotic hadronic matter. Indeed, the Z(4430) joins a long list of other putative exotic states, several of which have been reported in the past few years.

Although hadronic exotics such as glueballs, hybrids, and multiquark states have been long expected, the discussion of these states is primarily at the level of conjecture. Certainly, if the confirmation of the Z(4430) marks the beginning of the exploration of a new sector of matter, the current phenomenology concerning quark interactions will need to be radically overhauled. A compelling, unified understanding of the new states has not yet emerged. The gap between theory and experiment remains a major deficiency in our current level of understanding of elementary particle physics.

This gap has its roots in the famously difficult problem of solving QCD in its many-body, strongly interacting, relativistic regime. Effective field theories are inoperable in the excited spectrum, lattice field theory has difficulties with weakly bound diffuse systems, and extant models are insufficiently well-constrained to be confidently applied to exotic states. An instance where our lack of robust knowledge may have impact is in the analysis of the new states. For example, many Z states are seen in three body modes such as K pi J/psi, and correct interpretation of the results requires a good model of the K pi sub-dynamics.

It is expected that LHCb will continue to deliver new results in heavy quark spectroscopy for at least a decade. At the same time, BESIII at the Beijing Electron Positron Collider will continue its program to collect and analyze e+e- data in the energy region of the putative exotic states of charmonium. Furthermore, the GlueX experiment is due to start taking data in 2015. This experiment, situated at Hall D at JLab, is designed to discover and the explore the properties of light hybrid mesons. The COMPASS experiment at CERN has been, and will continue to be, very active in hadron spectroscopy. The PANDA experiment at FAIR is expected to start taking data in 2019; amongst its goals is the exploration of charmonium hybrids and other exotic states.

It is thus an opportune time to bring together a group of experts to assess the current experimental and theoretical situation concerning hadronic structure. The workshop will be structured to allow extensive discussions. A goal of the workshop will be to construct a concise list of questions that are meant to resolve the issues raised above, along with a suggested methodology for addressing those questions.