Polarization effects for the reaction $e^++e^-\to \bar p+p $ in presence of two--photon exchange - Lecture Notes

TL;DR

This paper provides a detailed pedagogical derivation of polarization observables in electron-positron annihilation into nucleon-antinucleon pairs, considering one- and two-photon exchange mechanisms and their impact on form factors.

Contribution

It introduces a comprehensive method to derive polarization observables in annihilation reactions with two-photon exchange, emphasizing model-independent properties of form factors.

Findings

Derived general expressions for cross sections and polarization observables.

Expressed observables in terms of generalized form factors.

Suggested strategies for extracting physical form factors in presence of two-photon exchange.

Abstract

The aim of this work is to give a pedagogical derivation of polarization observables for the annihilation reaction $e^+ + e^- \to N+ \bar N$. The reaction mechanism is one photon + two photon exchange, the last is described by axial parametrization. After deriving the general expressions for the cross section of a binary process, the matrix element is written in terms of three complex amplitudes. The method to derive polarization observables is detailed and all expressions are given in terms of generalized form factors. The strategy for determining physical form factors in annihilation reactions in presence of two photon exchange is suggested, on the basis of model independent properties of the relevant observables.