Progress towards a new microwave measurement of the hydrogen n=2 Lamb shift: a measurement of the proton charge radius

We propose to make a more precise measurement of the atomic hydrogen n=2 Lamb shift using the Ramsey method of separated oscillatory fields. This new measurement (with an anticipated uncertainty of 2 kHz -- 5 times more accurate than the 1981 measurement of Lundeen and Pipkin), along with existing precise atomic theory calculations, will allow for a new determination of the proton charge radius to an accuracy of 0.6 percent. The measurement will shed light on the 5$\sigma$ discrepancy between proton radius recently obtained from muonic hydrogen [Pohl, et al, Nature 466, 213 (2010)] and the CODATA value.