Gil Paz
Wayne State University, Detroit
Recently, the charge radius of the proton was extracted for the first time from the Lamb shift in muonic hydrogen [1]. Very surprisingly, the value is more than five standard deviations away from the regular hydrogen result. The extraction of the proton radius from muonic hydrogen depends on a theoretical input. In this talk I will describe the study, done together with Richard J. Hill, of the hadronic uncertainty in the theoretical prediction, using the tool of an effective field theory, namely NRQED [2]. I will also describe the model-independent extraction of the charge radius from electron-proton scattering. We have shown that previous extractions, spanning a period of over 40 years, have underestimated their error sometimes by a factor of two or more [3].
[1] R. Pohl et al., Nature 466, 213 (2010), A. Antognini et al., Science 339, 417 (2013)
[2] R.J. Hill, G. Paz, PRL 107, 160402 (2011)
[3] R.J. Hill, G. Paz, PRD 82, 113005 (2010)
