Kovalev, A.I
E+ E- --> GLUON X
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Test of QCD analytic predictions for the multiplicity ratio between gluon and quark jets.

The OPAL collaboration Alexander, G. ; Allison, John ; Altekamp, N. ; et al.
Phys.Lett.B 388 (1996) 659-672, 1996.
Inspire Record 423486 DOI 10.17182/hepdata.47714

Gluon jets with about 39 GeV energy are identified in hadronic Z 0 decays by tagging two jets in the same hemisphere of an event as quark jets. Identifying the gluon jet to be all the particles observed in the hemisphere opposite to that containing the two tagged jets yields an inclusive gluon jet definition corresponding to that used in analytic calculations, allowing the first direct test of those calculations. In particular, this jet definition yields results which are only weakly dependent on a jet finding algorithm. We find r ch. =1.552±0.0041 ( stat ) ±0.061 ( syst. ) for the ratio of the mean charged particle multiplicity in gluon jets to that in light quark uds jets, where the uds jets are identified using an inclusive jet definition similar to that used for the gluon jets. Our result is in general agreement with the prediction of a recent analytic calculation which incorporates energy conservation into the parton shower branching processes, but is considerably smaller than analytic predictions which do not incorporate energy conservation.

2 data tables
Table 1

Mean charged particle multiplicity in gluon jets.

Table 2

Mean charged particle multiplicity in single hemisphere light quark jets.


Measurement of the longitudinal, transverse and asymmetry fragmentation functions at LEP

The OPAL collaboration Akers, R. ; Alexander, G. ; Allison, John ; et al.
Z.Phys.C 68 (1995) 203-214, 1995.
Inspire Record 395450 DOI 10.17182/hepdata.48040

The fragmentation function for the process e+e−→h+X, whereh represents a hadron, may be decomposed into transverse, longitudinal and asymmetric contributions by analysis of the distribution of polar production angles. A number of new tests of QCD have been proposed using these fragmentation functions, but so far no data have been published on the separate components. We have performed such a separation using data on charged particles from hadronic Z0 decays atOpal, and have compared the results with the predictions of QCD. By integrating the fragmentation functions, we determine the average charged particle multiplicity to be\(\overline {n_{ch} }= 21.05 \pm 0.20\). The longitudinal to total cross-section ratio is determined to be σL/σtot=0.057±0.005. From the longitudinal fragmentation function we are able to extract the gluon fragmentation function. The connection between the asymmetry fragmentation function and electroweak asymmetrics is discussed.

4 data tables
Table 1

Transverse component of the fragmentation function.

Table 2

Longitudinal component of the fragmentation function.

Table 3

Asymmetry component of the fragmentation function.

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