Speaker
Description
We present a recursive quantum mechanical model for the fragmentation of a string stretched between a quark and an antiquark with entangled spin states. The quarks are assumed to be produced in the $𝑒^+𝑒^−$ annihilation process via the exchange of a virtual photon and the correlations between their spin states are described by a joint spin density matrix. The string fragmentation process is formulated at the amplitude level by using the splitting matrices of the recent string+${}^3𝑃_0$ model of polarized quark fragmentation with pseudoscalar and vector meson emissions, and accounts for the systematic propagation of the spin correlations in the fragmentation chain. The model is formulated as a recursive recipe suitable for a Monte Carlo implementation and it is implemented in the Pythia 8.3 event generator allowing for the first time to simulate the $𝑒^+𝑒^−$ annihilation process to hadrons with quark spin effects. After validating the generator, we carry simulations of $e^+e^-$ annihilations and obtain the results for the Collins asymmetries for back-to-back hadrons. The comparisons of the simulation results with data from BELLE, BABAR and BESIII experiments are presented and discussed.
