Extending StringSpinner to handle vector-meson spin

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+P03 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+P03 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. New version program summaryProgram Title: StringSpinnerCPC Library link to program files:https://doi.org/10.17632/37jrpmyz3t.2Developer's repository link:https://gitlab.com/albikerbizi/stringspinner.gitLicensing provisions: GNU GPL v2 or laterProgramming language:C++, FortranJournal reference of previous version: Comput. Phys. Commun. 272 (2022) 108234.Does the new version supersede the previous version?: YesReasons for the new version: Vector meson emission and decay is required for a more complete simulation of the DIS final states.Summary of revisions: The spin-dependence of the string fragmentation is extended to include the production and the decay of polarized vector mesons.Nature of problem: Vector meson contribute strongly to the final hadrons produced in DIS, and they can produce non-trivial effects on the spin-dependent observables.Solution method: Extend the previous version of StringSpinner to include polarized vector meson production and decay using a more complete model of polarized hadronization.