Thursday, May 23, 2013, 16:00
WHGA/Auditorium
J. McGovern, U. Manchester
Abstract:
In 2010 results of an experiment at PSI on the Lamb shift in muonic
hydrogen were published which implied a proton radius 4% - and at least 5 sigma -
below the previously accepted value. In the intervening time the older methods of
measuring this quantity - the hydrogen Lamb shift and electron-proton scattering -
have been re-evaluated without any errors being found, while further analysis of
the muonic data has increased the significance of the discrepancy.
This talk will review our knowledge of the proton radius and discuss one
particular aspect of its extraction from the muonic Lamb shift, the two-photon
exchange correction. Contrary to some claims, there seems no possibility that this is large
enough to explain the discrepancy.