On the definitions of the gamma*N -> N* helicity amplitudes

TL;DR

This paper clarifies the definitions and sign conventions for helicity amplitudes in gamma* N -> N* processes, facilitating consistent theoretical calculations and comparisons with experimental data.

Contribution

It provides standardized formulas and sign conventions for helicity amplitudes, addressing ambiguities in previous theoretical works.

Findings

Clearer definitions of sign conventions for amplitudes

Guidelines for consistent theoretical computations

Facilitates comparison with experimental data

Abstract

We present definitions and formulas that may be useful for a consistent computation of helicity amplitudes for the process gamma* N -> N* in theoretical approaches. Of particular importance is the correct determination of the common sign of the amplitudes and of the relative sign between the transverse (A12,A32) and longitudinal (S12) amplitudes. This clarification is necessary to clear up confusions present in theoretical works. Using the definitions presented in this paper will enable a direct comparison with amplitudes extracted from experimental data.