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      Nuclear Physics Colloquium
      
    Venue: Physics
          Building, Max-von-Laue-Str. 1, Seminar Room PHYS 2.116
      Time: Friday,
        May 19, 10:00am (s.t.)
      Contact: hees@fias.uni-frankfurt.de
    
    Proton
        remains puzzling
    Haiyan Gao (Duke University)
    Nucleons are building blocks of visible
      matter, and are responsible for more than 99% of the visible mass in the
      universe. Despite major progress made in the last two decades in
      understanding the proton spin "crisis",  discovered in the late 1980s
      by the European Muon Collaboration, the proton spin remains puzzling. At
      the same time, a new proton puzzle developed in the last several years
      concerning the proton charge radius, which is the charge weighted size of
      the proton. The ultrahigh precise value of the proton charge radius
      determined from muonic hydrogen Lamb shift measurements is about $7\sigma$
      smaller than the values determined from electron-proton scattering
      experiments and the CODATA value of the hydrogen Lamb shift measurements.
      In this talk I will review the latest situation concerning the proton spin
      and charge radius and discuss the 12 GeV SoLID project at Jefferson Lab
      and the PRad experiment, that was completed recently.
    
    
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