Global Positioning of Spin GPS Scheme for Half-Spin Massive Spinors

TL;DR

This paper introduces a new method for tracking complex phases and spin axes of half-spin Weyl spinors in high-energy physics scattering amplitudes, applicable to both massless and massive cases, enhancing Monte Carlo simulations.

Contribution

It provides a simple, flexible approach for spin and phase tracking in scattering amplitudes, improving the accuracy of simulations involving unstable fermions.

Findings

Numerical validation for tau tau-bar production and decay.

Enhanced capability for combining photon emission effects with spin.

Potential application in Monte Carlo event generators for heavy particles.

Abstract

We present a simple and flexible method of keeping track of the complex phases and spin quantization axes for half-spin initial- and final-state Weyl spinors in scattering amplitudes of Standard Model high energy physics processes. Both cases of massless and massive spinors are discussed. The method is demonstrated and checked numerically for spin correlations in tau tau-bar production and decay. Its main application will be in the forthcoming work of combining effects due to multiple photon emission (exponentiation) and spin, embodied in the Monte Carlo event generators for production and decay of unstable fermions such as the tau lepton, t-quark and hypothetical new heavy particles.