Two ­photon exchange corrections to the Lamb shift in muonic Helium-­4

We calculate the two-photon exchange corrections to the Lamb shift in muonic Helium-4 atom within a dispersion relation framework.  These corrections are crucial to obtaining the Helium-4 radius from Lamb shift data, with an accuracy well beyond what has been obtained from electron scattering data.  Part of the effort entailed making analytic fits to the electron-He4 quasielastic scattering data set, for purposes of doing the dispersion integrals.  The results will be compared to results obtained from the very different calculations using a potential model and an effective field theory calculation.