  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.
