Proton Size Anomaly

Vernon Barger, Cheng-Wei Chiang, Wai-Yee Keung, and Danny Marfatia
Phys. Rev. Lett. 106, 153001 – Published 11 April 2011


A measurement of the Lamb shift in muonic hydrogen yields a charge radius of the proton that is smaller than the CODATA value by about 5 standard deviations. We explore the possibility that new scalar, pseudoscalar, vector, and tensor flavor-conserving nonuniversal interactions may be responsible for the discrepancy. We consider exotic particles that, among leptons, couple preferentially to muons and mediate an attractive nucleon-muon interaction. We find that the many constraints from low energy data disfavor new spin-0, spin-1, and spin-2 particles as an explanation.

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  • Received 18 November 2010


© 2011 American Physical Society

Authors & Affiliations

Vernon Barger1, Cheng-Wei Chiang2,3,1, Wai-Yee Keung4, and Danny Marfatia5,1

  • 1Department of Physics, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA
  • 2Department of Physics and Center for Mathematics and Theoretical Physics, National Central University, Chungli, Taiwan 32001, Republic of China
  • 3Institute of Physics, Academia Sinica, Nankang, Taipei 11925, Republic of China
  • 4Department of Physics, University of Illinois, Chicago, Illinois 60607, USA
  • 5Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA

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Vol. 106, Iss. 15 — 15 April 2011

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