The strong coupling constant, αs, has been determined in hadronic decays of theZ0 resonance, using measurements of seven observables relating to global event shapes, energy correlatio
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
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.
The differential cross section for the reaction H2(γ,p)n has been measured at several center-of-mass angles ranging from 50° to 143° for photon energies between 0.8 and 1.8 GeV. The experiment was performed at the SLAC-NPAS facility with the use of the 1.6 GeV/c spectrometer to detect the high energy protons produced by a bremsstrahlung beam directed at a liquid deuterium target. Contributions from concurrent disintegration by the residual electron beam were determined by measuring the proton yield without the Cu photon radiator. At angles not very far from 90°, the energy dependence of the cross sections is consistent with predictions of scaling using counting rules for constituent quarks. At least one theoretical calculation based on a meson-baryon picture of the reaction is able to reproduce the magnitude and energy dependence of the 90° cross section. The angular distribution exhibits a large enhancement at backward angles at the higher energies.
THE QUOTED ERRORS ARE STATISTICAL ONLY.
The study of the K + total cross sections on a wide range of nuclei has revealed important modifications of the free-space K + -nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on 6 Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.
No description provided.
No description provided.
No description provided.
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.
The total cross section for pion production in the reaction pd→pdπ0 has been measured for bombarding energies from Tp=208.4 MeV to 294.6 MeV. This corresponds to maximum pion momenta η=pπ,c.m./mπc between 0.099 and 0.96. The experiment was performed using an electron-cooled proton beam and an internal deuterium gas jet target. The resulting σtot changes by almost four orders of magnitude over the covered energy range. The results are compared to a model which assumes quasi-free production via the pn→dπ0 elementary process.
Geometry 1.
Geometry 2.
No description provided.
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.
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.
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