Abstract
We present a model for Monte Carlo simulation of the fragmentation of a polarized quark. The model is based on string dynamics and the ${}^3P_0$ mechanism of quark pair creation at string breaking. The fragmentation is treated as a recursive process, where the splitting function of the subprocess $q \to h + q'$ depends on the spin density matrix of the quark $q$. The ${}^3P_0$ mechanism is parametrized by a complex mass parameter $\mu$, the imaginary part of which is responsible for single spin asymmetries. The model has been implemented in a Monte Carlo program to simulate jets made of pseudoscalar mesons. Results for single hadron and hadron pair transverse-spin asymmetries are found to be in agreement with experimental data from SIDIS and $e^+e^-$ annihilation. The model predictions on the jet-handedness are also discussed.
Highlights
The fragmentation of quarks into hadron jets is a nonperturbative QCD process and as such is still poorly understood theoretically
In order to study the transverse spin effects measured in semiinclusive deep inelastic scattering (SIDIS) off transversely polarized protons and in eþe− annihilation, fragmentation events have been generated for initial quarks fully polarized along a fixed yaxis orthogonal to the string axis
For the study of the asymmetries in the azimuthal distributions of the hadrons produced in eþe− annihilation a second sample of events has been generated with a fixed c.m. energy W 1⁄4 10 GeV corresponding to the BELLE energy
Summary
The fragmentation of quarks into hadron jets is a nonperturbative QCD process and as such is still poorly understood theoretically For this reason many simulation models based on the recursive splitting process q → h þ q0 [1,2] have been developed to account for the main jet properties, prepare high-energy experiments and analyze their results. The most elaborate one is the Lund symmetric model (LSM) [3], based on the semiclassical dynamics of a string or color flux tube This model is the basis of the fragmentation part in the event generator PYTHIA [4], which successfully describes the experimental data for different scattering processes. We remind that a different model of polarized quark fragmentation, based on the spin density matrix formalism within the extended quark-jet framework of Field and Feynman, has been recently proposed in Ref. We remind that a different model of polarized quark fragmentation, based on the spin density matrix formalism within the extended quark-jet framework of Field and Feynman, has been recently proposed in Ref. [13]
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