Spin versus helicity in processes involving transversity

TL;DR

This paper develops a spin formalism tailored for processes involving transversity, simplifying calculations compared to the traditional helicity approach, and applies it to specific processes including the quark dipole magnetic moment.

Contribution

It introduces a new spin formalism for transversity processes and establishes its correspondence with the helicity formalism, simplifying the analysis of such processes.

Findings

Spin formalism simplifies transversity process calculations.

Correspondence between spin and helicity formalisms is established.

Quark dipole magnetic moment is effectively treated within the spin formalism.

Abstract

We construct the spin formalism in order to deal in a direct and natural way with processes involving transversity which are now of increasing popularity. The helicity formalism which is more appropriate for collision processes of definite helicity has been so far used also to manage processes with transversity, but at the price of computing numerous helicity amplitudes generally involving unnecessary kinematical variables.In a second step we work out the correspondence between both formalisms and retrieve in another way all results of the helicity formalism but in simpler forms.We then compute certain processes for comparison.A special process:the quark dipole magnetic moment is shown to be exclusively treated within the spin formalism as it is directly related to the transverse spin of the quark inside the baryon.