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Departmental Colloquium

The Fascinating Structure of Hadrons: What have we learned about excited protons?  
Guest Speaker
Volker Crede  
Guest Affiliation
Florida State University, Physics Department  
Guest Affiliation Url  
Kanzo Nakayama  
Thursday, April 4, 2013 4:00 pm - 5:00 pm  
Physics Auditorium (Rm 202)  

Hadrons are composed of quarks and gluons held together by the strong force. They can be categorized into two families: baryons, three-quark states such as the proton and the neutron, as well as mesons, quark-antiquark states such as the pion. Other types of hadrons may exist and much effort is invested in state-of-the art experiments around the world to search for new forms of matter, but no current evidence conclusively suggests the existence of unconventional or exotic hadrons. The composite nature of these particles manifests itself in the existence of a rich spectrum of excited states. The properties of these resonances can be identified by systematic investigations using electromagnetic and strong probes, primarily with beams of electrons, photons, and pions. In the spectroscopy of baryon resonances, after decades of research, the fundamental degrees of freedom underlying the baryon excitation spectrum are still poorly understood. The search for hitherto undiscovered bu
t predicted resonances continues at many laboratories worldwide. Recent results from photo- and electro-production experiments provide intriguing indications for new states and shed light on the structure of some of the known nucleon excitations. The continuing study of available data sets with consideration of new observables and improved analysis tools have also called into question some of the earlier findings in the field. I will present the hadron spectroscopy program at Jefferson Laboratory and will discuss recent progress toward understanding baryon resonances.