Particle multiplicity of unbiased gluon jets from e⁺e⁻ three-jet events
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Colleges, School and Institutes
The charged particle multiplicities of two- and three-jet events from the reaction e(+)e(-) --> Z(0) --> hadrons are measured for Z(0) decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jet,., are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from Y and Z(0) decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio r equivalent to N-g/N-q of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, r((1)) equivalent to (dN(g)/d(y))/(dN(q)/dy), and of curvatures, r((2)) equivalent to (d(2)N(g)/dy(2))/(d(2)N(q)/dy(2)), where y specifies the energy scale. At 30 GeV, we find r = 1.422 +/- 0.051, r((1)) = 1.761 +/- 0.071 and 7,(2) = 1.98 +/- 0.13, where the uncertainties are the statistical and systematic terms added in quadrature. These results axe in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of N-g and N-q to determine ail effective value of the ratio of QCD color factors, C-A/C-F.,. Our result, C-A/C-F = 2.23 +/- 0.14 (total), is consistent with the QCD value of 2.25.
|Number of pages||17|
|Journal||European Physical Journal C|
|Publication status||Published - 1 Apr 2002|