Inserting physics associated with the transverse polarization of the quarks into a standard Monte Carlo generator, without touching the code itself

TL;DR

This paper introduces a method to incorporate the effects of quark transverse polarization into standard Monte Carlo generators like Pythia without modifying their source code, enabling simulation of polarization-dependent phenomena.

Contribution

It presents techniques to modify Monte Carlo output at the event level to include transverse polarization effects, specifically applied to generate Collins asymmetry in pion pairs.

Findings

Successfully modified Pythia events to produce nonzero Collins function

Demonstrated the generation of cos(Phi1+Phi2) asymmetry in pion pairs

Provided a practical approach to include polarization effects without changing generator code

Abstract

The transverse polarization of a quark is a degree of freedom that is not taken into account in the most commonly used Monte Carlo generators. For the case "e^+e^- -> hadrons" I show that it is possible to use these generators to simulate processes where the parent quark and antiquark are transversely polarized and the fragmentation process is affected by this polarization. The key point is that it is possible to obtain this without touching the generator code at all. One only works on the parton-level and hadron-level outputs that the Monte Carlo code has produced, modifying them in a correlated way. A group of techniques is presented to obtain this, matching the most obvious needs of a user (in particular: reproducing a pre-assigned final distribution). As an example these methods are applied to modify Pythia-generated events to obtain a nonzero Collins function and a consequent cos(Phi1+Phi2)-asymmetry of pion pairs.