General analysis of two--photon exchange in elastic electron--$^4He$ scattering and $e^++e^-\to π^++π^-.$

G. I. Gakh; E. Tomasi--Gustafsson

doi:10.1016/j.nuclphysa.2010.03.005

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arXiv · 0801.4646

General analysis of two--photon exchange in elastic electron--$^4He$ scattering and $e^++e^-\to π^++π^-.$

G. I. Gakh·E. Tomasi--Gustafsson

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Abstract

Using a general parametrization of the spin structure of the matrix element for the elastic $e^-+^4He$ scattering and for the annihilation $e^++e^-\to π^++π^-$ reactions in terms of two complex amplitudes, we derive general properties of the observables in presence of two--photon exchange. We show that this mechanism induces a specific dependence of the differential cross section on the angle of the emitted particle. We reanalyze the existing experimental data on the differential cross section, for elastic electron scattering on $^4He$, in the light of this result.

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G. I. Gakh, E. Tomasi--Gustafsson. 2008-01-30. General analysis of two--photon exchange in elastic electron--$^4He$ scattering and $e^++e^-\to π^++π^-.$. https://doi.org/10.1016/j.nuclphysa.2010.03.005

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