The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z 0 decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is α s ( M Z ) = 0.124 −0.007 +0.006 (exp) ± 0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence.
SIG(Q=BQ, Q=CQ, Q=UDS) corresponds to BQ, CQ, and U,D,S quarks fragmentation into charged hadron.
alpha_s was evaluated from the scaling violation of the fragmentation func tions. The data from other experiments are used for the fitting procedure.
We have measured the total normalized cross section R for the process e + e − → hadrons at centre-of-mass energies between 14.0 and 46.8 GeV based on an integrated luminosity of 60.3 pb −1 . The data are well described by the standard SU(3) c ⊗SU(2) L ⊗U(1) model with the production of the five known quarks. No open production of a sixth quark with charge 2/3 or 1/3 occurs below a centre-of-mass energy of 46.6 or 46.3 GeV, respectively. A fitting procedure which takes the correlations between measurements into account was used to determine the electroweak mixing angle sin 2 θ w and the strong coupling constant α s ( S ) in second-order QCD. We applied this procedure to the CELLO data and in addition included the data from other experiments at PETRA and PEP. Both fits give consistent results. The fit to the combined data yields α s (34 2 GeV 2 ) = 0.165±0.030, and sin 2 θ w = 0.236±0.020. Fixing sin 2 θ w at the world average value of 0.23 yields α s (34 2 GeV 2 ) = 0.169±0.025.
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We report a high-precision measurement of the ratio R of the total cross section for e+e−→hadrons to that for e+e−→μ+μ−, at a center-of-mass energy of 29.0 GeV using the MAC detector. The result is R=3.96±0.09. This value of R is used to determine a value of the strong coupling constant αs of 0.23±0.06, nearly independent of fragmentation models. Two different analysis methods having quite different event-selection criteria have been used and the results are in agreement. Particular attention has been given to the study of systematic errors. New higher-order QED calculations are used for the luminosity determination and the acceptance for hadrons.
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The topology of hadronic e + e − annihilation events has been analysed using the sphericity tensor and a cluster method. Comparison with quark models including gluon bremsstrahlung yields good agreement with the data. The strong-coupling constant is determined in 1st order QCD to be α S =0.19±0.04 (stat) ± 0.04 (syst.) at 22 GeV and α S =0.16 ±0.02± 0.03 at 34 GeV. The differential cross section with respect to the energy fraction carried by the most energetic parton agrees with the prediction of QCD, but cannot be reproduced by a scalar gluon model. These results are stable against variations of the transverse momentum distribution of the fragmentation function within the quoted errors.
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