The Radius of the Proton: Size Does Matter.

The measurement by Pohl et al. [1] of the 2S1/2F = 1 to 2P3/2F = 2 transition in muonic hydrogen and the subsequent analysis has led to a conclusion that the rms charge radius of the proton differs from the accepted (CODATA [2]) value by approximately 4%, leading to a 4.9σ discrepancy. We investigate the muonic hydrogen spectrum relevant to this transition using bound-state QED with Dirac wave-functions and comment on the extent to which the perturbation-theory analysis which leads to the above conclusion can be confirmed. [ABSTRACT FROM AUTHOR]