Abstract
The low momentum transfer region of strong-interaction processes may be discussed in terms of one-pion-exchange graphs. This success of "extrapolation to poles" suggests, as an extension, "extrapolation to cuts" corresponding to low-mass intermediate states containing two or more particles. We find that this extrapolation may be performed in the case of electromagnetic interactions, owing to the vanishing photon mass. For small-angle scattering of relativistic electrons in a pure Coulomb field, , where is given precisely by the one-photon pole and (obtained exactly to all orders in ) comes from the many-photon terms. For scattering by finite nuclei we further find that, for fixed momentum transfer, the ratio of second to first Born approximation decreases as at high energies. This leads to a simple approximate formula for the ratio of electron and positron scattering, and to a simple method of determining the charge form factors of intermediate- nuclei.
- Received 28 August 1961
DOI:https://doi.org/10.1103/PhysRev.125.1394
©1962 American Physical Society