Extending StringSpinner to handle vector-meson spin

TL;DR

This paper extends the StringSpinner package within PYTHIA 8 to include vector meson production, enabling more comprehensive simulations of polarized semi-inclusive deep inelastic scattering and spin effects in hadronization.

Contribution

The authors develop a major extension of StringSpinner to incorporate vector mesons, enhancing the modeling of spin-dependent hadronization processes in PYTHIA 8.

Findings

Enables simulation of vector meson production with spin effects

Allows study of transverse-spin effects in vector mesons

Works with PYTHIA 8.3 for more complete DIS event modeling

Abstract

Quark spin effects in hadronization were recently included in the PYTHIA 8 Monte Carlo event generator for the simulation of the deep inelastic scattering (DIS) process off a polarized proton or neutron target. The spin effects were activated via the external StringSpinner package, which is based on the string+${}^3P_0$ model of polarized hadronization, and were restricted to the production of pseudoscalar mesons in string fragmentation. The struck quark polarization could either be calculated using parametrizations of the transversity PDFs or be freely specified. In this article we present a major extension of StringSpinner that includes vector meson production in the PYTHIA 8 string fragmentation. The spin-dependent emission and decay processes of the vector mesons are described using the string+${}^3P_0$ model, which systematically accounts for the quark-spin degree of freedom in the fragmentation chain. The new package works with the version 8.3 of the PYTHIA event generator and it allows for a more complete and quantitative simulation of the final states in polarized semi-inclusive DIS events. Also, it can be used to study the transverse-spin effects for the production of vector mesons. After describing the new version of StringSpinner, examples of its usage in semi-inclusive DIS events are presented.