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Properties of Heavy Quark Jets Produced by Ee− Annihilation at 29 GeV.

Properties of Heavy Quark Jets Produced by Ee− Annihilation at 29 GeV.
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Release: 1985
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The Mark II detector in the ee− storage ring PEP at the Stanford Liner Accelerator Center (SLAC) is used to measure selected properties of hadronic events corresponding to produced bottom or charm quarks. Heavy flavor enrichment is accomplished by tagging events with prompt electrons or muons. Differences between bottom, charm and average jets are observed for momentum, transverse momentum, rapidity and jet mass distributions. A detailed study of the charged multiplicity of b- and c-enriched events finds the mean multiplicity of bottom and charm events to be 16.2 +- 0.5 +- 1.0 and 13.2 +- 0.5 +- 0.9, respectively, where the first error is statistical and the second is systematic. The corresponding 'non-leading' multiplicities of charged particles accompanying the pair of heavy hadrons are 5.2 +- 0.5 +- 0.9 for bottom, and 8.0 +- 0.5 +- 0.9 for charm. We find from these non-leading multiplicities that bottom and charm hadrons fragment with mean energy fractions of z/sub b/ = 0.79/sub -0.05//sup +0.10/ and z/sub c/ = 0.60/sub -0.11//sup +0.09/. These results confirm the expected hard fragmentation of heavy quarks and agree with previous measurements based on leptonic inclusive spectra and D* fragmentation. 48 refs., 29 figs.

Properties of Jets in High-E

Properties of Jets in High-E
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Release: 1983
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The properties of jets in high-E/sub tau/ events produced in pp collisions at .sqrt.s = 63 GeV have been studied at the CERN Intersecting Storage Rings. The fragmentation of the jets is found to be similar to that of jets produced in ee− annihilation. The jets are wider than calculated from a constituent scattering model with no hard bremsstrahlung component. The charge correlations of positive and negative particles show differences consistent with expectation from valence-quark scattering. 11 references.

Physics Briefs

Physics Briefs
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Total Pages: 864
Release: 1992
Genre: Physics
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Study of Quark Fragmentation at 29 GeV.

Study of Quark Fragmentation at 29 GeV.
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Release: 1983
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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.

Energy Research Abstracts

Energy Research Abstracts
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Total Pages: 872
Release: 1988
Genre: Power resources
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Study of Quark Fragmentation in Ee− Annihilation at 29 GeV

Study of Quark Fragmentation in Ee− Annihilation at 29 GeV
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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.

Comparison of Three-jet and Radiative Two-jet Events in Electron-positron Annihilation at 29 GeV.

Comparison of Three-jet and Radiative Two-jet Events in Electron-positron Annihilation at 29 GeV.
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Release: 1986
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By comparing 3-jet (ee− .-->. q anti q g) and radiative 2-jet (ee− .-->. q anti q .gamma.) events from electron-positron annihilation, we have studied the local and global effects of the presence of a hard bremsstrahlung gluon in hadronic events. Detector and event selection efficiencies and biases affect these two kinds of events almost equally because they have very similar kinematics and topologies. Accurate comparisons of q anti q g and q anti q .gamma. events can therefore be made. Globally, we observe a depletion of hadrons in q anti q g events relative to q anti q .gamma. events on the opposite side of the event plane from the gluon, in the angular region between the q and anti q jets. This depletion is shown to be in agreement with the predictions of Quantum Chromodynamics (QCD). The existence of this effect demonstrates that the presence of a gluon significantly alters the color forces and hence the fragmentation process in hadronic events. We also use these q anti q .gamma. and q anti q g events to compare low energy (4.5 GeV) gluon and quark jets. Our data indicate that gluon jets have softer x/sub p/ distributions than quark jets, while the transverse momentum distributions of these two types of jets are identical within our errors. Although we are unable to determine if the multiplicities of gluon (n/sub /) and quark (n/sub q/) jets are different, the ratio n/sub g//n/sub q/ = 9/4 predicted asymptotically in QCD would not be consistent with our data.