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

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.