The production rate of final state photons in hadronic Z 0 decays is measured as a function of y cut = M ij 2 / E cm 2 the jet resolution parameter and minimum mass of the photon-jet system. Good agreement with the theoretical expectation from an O( αα s ) matrix element calculation is observed. Comparing the measurement and the prediction for y cut = 0.06, where the experimental systematic and statistical errors and the theoretical uncertainties are small, and combining this measurement with our result for the hadronic width of the Z 0 , we derived partial widths of up and down type quarks to be Γ u = 333 ± 55 ± 72 MeV and Γ d = 358 ± 37 ± 48 MeV in agreement with the standard model expectations. We compare our yield with the QCD shower models including photon radiation. At low γ cut JETSET underestimates the photon yield, and ARIADNE describes the production rate well.
It is assumed that the couplings of various up quarks to be the same.
It is assumed that the couplings of various down type quarks to be the same.
We present a measurement of the forward-backward charge asymmetry in hadronic decays of the Z 0 using data collected with the OPAL detector at LEP. The forward-backward charge asymmetry was measured using a weight function method which gave the number of forward events on a statistical basis. In a data sample of 448 942 hadronic Z 0 decays, we have observed a charge asymmetry of A h = 0.040±0.004 (stat.)±0.006 (syst.)±0.002 (B 0 B 0 mix.), taking into account the effect of B 0 B 0 mixing. In the framework of the standard model, this asymmetry corresponds to an effective weak mixing angle averaged over five quark flavours of sin 2 θ W = 0.2321 ± 0.0017 ( stat. ) ± 0.0027 ( syst. ) ± 0.0009 (B 0 B 0 mix.). The result agrees with the value obtained from the Z 0 line shape and lepton pair forward-backward asymmetry.
No description provided.
The second systematic error is due to the uncertainty in the correction for B.BBAR mixing which had been applied to the data.
The second systematic error is due to the uncertainty in the correction for B.BBAR mixing which had been applied to the data.
The production of the octet and decuplet baryons Λ, Ξ − , Σ (1385) ± , Ξ(1530) 0 and Ω − and the corresponding antibaryons has been measured in a sample of 485 000 hadronic Z 0 decays. Results on differential and integrated cross sections are presented. The differential cross section of Λ baryons is found to be softer than the one predicted by the Jetset and Herwig Monte Carlo generators. The measured decuplet yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is used. Comparisons of the momentum spectra for Λ and Ξ − with the predictions of an analytical QCD formula are also presented.
No description provided.
No description provided.
No description provided.
Results are reported of a study of neutral vector meson production in multihadronicZ0 decays in the OPAL experiment at LEP. Pions and kaons have been identified by specific ionisation energy loss andK±π∓ andK+K− mass spectra have been fitted, in bins of the scaled momentum variablexp, to combinations of resonance signals and non-resonant backgrounds. Rates are given forK*(892)° and ø(1020), and production cross sections are compared to the predictions of Monte Carlo models. Overall multiplicities have been determined as 0.76±0.07±0.06K*(892)° and 0.086±0.015±0.010 ø(1020) per hadronicZ0 decay (the quoted errors are respectively statistical and systematic). Momentum dependent distortions of the ππ mass spectra, possibly associated indirectly with Bose-Einstein effects, have prevented reliable measurement of the ρ(770)° cross section in this study.
No description provided.
No description provided.
No description provided.
Measurements are presented of the inclusive cross section for K ∗ (892) ± production in hadronic decays of the Z 0 using a sample of about half a million events recorded with the OPAL experiment at LEP. Charged K ∗ mesons are reconstructed in the decay channel K 0 S π ± . A mean rate of 0.72±0.02±0.08 K ∗ mesons per hadronic event is found. Comparison of the results with predictions of the JETSET and HERWIG models shows that JETSET overestimates the K ∗± production cross section while HERWIG is consistent with the data.
No description provided.
No description provided.
From a sample of 146900 hadronicZ0 decays recorded by the OPAL detector at LEP, we have studied the azimuthal correlations of particles in hadronic events. It is expected that these correlations are sensitive to interference effects in QCD. We have compared the data to QCD Monte Carlo models which include and which do not include interference effects. We find that the distributions of azimuthal correlations are not reproduced by the parton shower models we have tested unless interference effects are included, no matter which hadronisation scheme is used.
Corrected data for the EMMC.
Corrected data for the TPAC.
The cross section and jet rates ofZ0 decays into photons and quarks are compared with matrix element Monte Carlos ofO(ααs). Good agreement is found between data and theoretical predic
Corrected number of hadronc events that have a final state photon per 1000 multhadronic Z0 decays, using the E0 scheme.
Corrected number of hadronc events that have a final state photon per 1000 multhadronic Z0 decays, using the Durham scheme.
Corrected number of events that have a final state photon with 1, 2, 3, or more jets per 1000 multhadronic Z0 decays, using the E0 scheme.
New measurements of the hadronic and leptonic cross sections and of the leptonic forward-backward asymmetries ine+e− collisions are presented. The analysis includes data recorded up to the end of 1991 by the OPAL experiment at LEP, with centre-of-mass energies within ±3 GeV of the Z0 mass. The results are based on a recorded total of 454 000 hadronic and 58 000 leptonic events. A model independent analysis of Z0 parameters based on an extension of the improved Born approximation is presented leading to test of lepton universality and an interpretation of the results within the Standard Model framework. The determination of the mass and width of the Z0 benefit from an improved understanding of the LEP energy calibration.
Statistical and systematic point-to-point errors included. There is an additional 0.2 pct overall systematic uncertainty.
Systematic error of 0.45 pct not included.
Systematic error of 0.25 pct not included.
Quark and gluon jets with equal energies are identified in three-jet hadronicZ0 events, using reconstructed secondary vertices from heavy quark decay in conjunction with energy orderi
No description provided.
The production dynamics of baryon-antibaryon pairs are investigated using hadronic Z 0 decays, recorded with the OPAL detector, which contain at least two identified Λ baryons. The rapidly difference for Λ Λ pairs shows the correlations expected from models with a chain-like production of baryon-antibaryon pairs. If the baryon number of a Λ is compensated by a Λ , the Λ is found with a probability of 53% in an interval of ±0.6 around the Λ rapidity. This correlation strength is weaker than predicted by the Herwig Monte Carlo and the Jetset Monte Carlo with a production chain of baryon-antibaryon, and stronger than predicted by the UCLA model. The observed rapidity correlations can be described by the Jetset Monte Carlo with a dominant production chain of baryon-meson-antibaryon, the popcorn mechanism. In addition to the short range correlations, one finds an indication of a correlation of Λ Λ pairs in opposite hemispheres if both the Λ and the Λ have large rapidities. Such long range correlations are expected if the primary quark flavours are compensated in opposite hemispheres and if these quarks are found in energetic baryons. Rates for simultaneous baryon and strangeness number compensation for Λ Λ , Ξ − Ξ + and Ξ − Λ ( Λ + Λ ) are measured and compared with different Monte Carlo models.
No description provided.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified LAMBDA(LAMBDABAR). CT.= Data read from plot.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified XI-(XIBAR+). CT.= Data read from plot.
Forum