Monte Carlo results on the Collins asymmetries in $e^+e^-$ annihilation

TL;DR

This paper introduces a Monte Carlo simulation incorporating quark spin effects to study Collins asymmetries in electron-positron annihilation, achieving results consistent with experimental data.

Contribution

It integrates the StringSpinner package with Pythia 8 to simulate quark spin effects in $e^+e^-$ annihilation, providing a novel approach to modeling Collins asymmetries.

Findings

Simulated Collins asymmetries agree with BELLE and BABAR data.

The method effectively reproduces experimental asymmetries.

The approach offers a new tool for spin effect studies in particle physics.

Abstract

The quark spin effects have been introduced in the Pythia 8 Monte Carlo event generator for the simulation of $e^+e^-$ annihilation by interfacing the generator with the StringSpinner package. The package allows to simulate quark spin effects in the string fragmentation routine of Pythia by using the string+${}^3P_0$ model, recently applied to the fragmentation of a string stretched between a quark-antiquark pair with correlated spin states. StringSpinner is used to carry out simulations of $e^+e^-$ annihilation at the center of mass energy of $10.6\,\rm{GeV}$. The Collins asymmetries are extracted from the simulated data for back-to-back pion pairs using both the thrust axis method and the hadronic plane method. The results are compared with the data from the BELLE and BABAR experiments, finding a satisfactory agreement.