The Proton Radius Puzzle

  title={The Proton Radius Puzzle},
  author={Carl E. Carlson},
  journal={Progress in Particle and Nuclear Physics},
  • C. Carlson
  • Published 2015
  • Physics
  • Progress in Particle and Nuclear Physics
Abstract The proton size, specifically its charge radius, was thought known to about 1% accuracy. Now a new method probing the proton with muons instead of electrons finds a radius about 4% smaller, and to boot gives an uncertainty limit of about 0.1%. We review the different measurements, some of the calculations that underlie them, some of the suggestions that have been made to resolve the conflict, and give a brief overview new related experimental initiatives. At present, however, the… Expand

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