This study uses the full equations of motion of the massless relativistic string as a phenomenological model of color flux tubes in the process of hadronization in electron-positron annihilation. Perturbatively generated sets of partons are mapped onto color singlet strings, which fragment according to a generalization of the covariant decay law for point relativistic particles. String evolution is terminated when string masses are a few GeV above particle production threshold. Low-mass strings are decayed into primary hadrons using a parameterization of low-mass data. The complete model, which factorizes event evolution into three stages including perturbative QCD, string fragmentation and parameterized low-mass decays, is implemented as a Monte Carlo program known as the Caltech-II model of hadronization. An exact formalism is presented for the fragmentation function of heavy quarks within the string model.
The main results are, in their order of appearance: (1) The kinematics of the evolution and decay of arbitrarily complex massless relativistic strings is most conveniently expressed in terms of momentum currents. (2) The Caltech-II model, which uses the momentum current formalism to describe relativistic strings, provides a good description of electron-positron annihilation data over a wide range of center-of-mass energies. (3) Introducing transverse momentum at the sites of string breaks is conceptually necessary and may be required to further improve agreement between the Caltech-II model and data. (4) Fragmentation functions are predictions, not assumptions, of the string model in Caltech-II. The fragmentation function of heavy quarks in the Caltech-II string model is shown to exhibit the behavior expected from model-independent arguments. The discovery of the top quark or additional generations of heavy quarks will be a testing ground for future studies of hadronization.
