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This paper presents the charged particle multiplicity distributions for ee− annihilation at .sqrt.s = 29 GeV measured in the High Resolution Spectrometer. The data, which correspond to an integrated luminosity of 185 pb−1, were obtained at the ee− storage ring PEP. The techniques used to obtain the original distributions from the observed prong numbers are discussed. The multiplicity distribution of the charged particles with a two jet selection has a mean value Nch = 13.02 +- 0.03 +- 0.5; and a dispersion D = 3.84 +- 0.02 +- 0.1. The mean multiplicity increases with the event sphericity. No correlation is observed between the multiplicities in the two jets that characterize most of the events. For the single jets a value of D = 2.71 +- 0.02 +- 0.06 is measured which gives further support the idea of independent jet fragmentation. When compared with e+e− data at other energies, the multiplicity distributions exhibit the scaling behavior in the mean first suggested by Koba, Nielsen and Olsen (KNO). The KNO distribution in the central rapidity interval is broader than that for the whole rapidity span and agrees well with the generalized Bose-Einstein formula for three independent sources. 17 refs., 14 figs.
The study of multi-particle final state in high-energy reactions has a long history. Detailed studies of hadronic interactions at Fermilab and at the CERN ISR have shown that particles are emitted in clear jets of hadrons along the beam directions. For the highest energies, a small fraction of events contains large-angle jets originating from hard collisions, in addition to the beam and target fragmentation products. The clearest observation of jets has been in high-energy ee− reactions. Hadronic interactions contain 5 or 6 valence quarks already in the initial state. The final state in ee− annihilation represents at the parton level a relatively simple dynamical system: a q anti q state plus possibly a hard gluon therefore jets produced in e+e− annihilation have to be considered as the cleanest ones. The study of their properties can help, not only to understand quark fragmentation but may also serve as an important tool in the analysis of the much more complex mechanism in hadronic interactions. In this paper we present preliminary results of the overall features of our first sample of e+e− annihilation events at 29 GeV. The data were taken using the High Resolution Spectrometer (HRS) operated at the PEP storage ring at the Stanford Linear Accelerator Center.
consequence of the high decay multiplicity of the leading charmed particle.
We examine the distribution of particles in the three jet events of e e annihilation. The data was collected with the PEP-4/Time Projection Chamber detector at 29 GeV center-of-mass energy at PEP. The experimental distributions are compared to the predictions of several fragmentation models which describe the transition of quarks and gluons into hadrons. In particular, our study emphasizes the three fragmentation models which are currently in widest use: the Lund string model, the Webber cluster model and the independent fragmentation model. These three models each possess different Lorentz frame structures for the distribution of hadron sources relative to the overall event c.m. in three jet events. The Lund string and independent fragmentation models are tuned to describe global event properties of our multihadronic annihilation event sample. This tuned Lund string model provides a good description of the distribution of particles between jet axes in three jet events, while the independent fragmentation model does not. We verify that the failure of the independent fragmentation model is not a consequence of parameter tuning or of model variant. The Webber cluster model, which is untuned, does not describe the absolute particle densities between jets but correctly predicts the ratios of those densities, which are less sensitive to the tuning. These results provide evidence that the sources of hadrons are boosted with respect to the overall center-of-mass in three jet events, with components of motion normal to the jet axes. The distribution of particles close to jet axes provides additional support for this conclusion. 94 refs.