The couplings of the Z 0 to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at centre of mass energies near to the mass of the Z 0 . The data are consistent with lepton universality. Using a parametrisation of the lepton pair differential cross section which assumes that the Z 0 has only vector and axial couplings to leptons, the charged leptonic partial decay width of the Z 0 is determined to be Г ol+ol− = 83.1±1.9 MeV and the square of the product of the effective axial vector and vector coupling constants of the Z 0 to charged leptons to be a ̌ 2 ol v ̌ 2 ol = 0.0039± 0.0083 , in agreement with the standard model. A parametrisation in the form of the improved Born approximation gives effective leptonic axial vector and vector coupling constants a ̌ 2 ol = 0.998±0.024 and v ̌ 2 ol = 0.0044±0.0083 . In the framework of the standard model, the values of the parameters ϱ z and sin 2 θ w are found to be 0.998±0.024 and 0.233 +0.045 −0.012 respectively. Using the relationship in the minimal standard model between ϱ z and sin 2 θ w , the results sin 2 θ SM w = 0.233 +0.007 −0.006 is obtained. Our previously published measurement of the ratio of the hadronic to the leptonic partial width of the Z 0 is update: R z = 21.72 +0.71 −0.65 .
Cross sections corrected for the effects of efficiency and kinematic cuts. Errors have systematic effects folded.
Acceptance corrected cross sections. Statistical errors only.
Acceptance corrected cross sections. Statistical errors only.
We have measured the partial width and forward-backward charge asymmetry for the reaction e + e - →Z 0 →μ + μ - (γ). We obtain a partial width Γ μμ of 83.3±1.3(stat)±0.9(sys) MeV and the following values for the vector and axial vector couplings: g v =−0.062 −0.015 +0.020 and g A =−0.497 −0.005 +0.005 . From our measurement of the partial width and the mass of the Z 0 boson we determine the effective electroweak mixing angle, sin 2 θ w =0.232±0.005, and the neutral current coupling strength parameter, ϱ =0.998±0.016.
No description provided.
Forward backward charge asymmetry.
No description provided.
We study the inclusive momentum distribution of charged particles in multihadronic events produced in e + e − annihilations at E CM ∼ M (Z 0 ). We find agreement with the analytical formulae for gluon production that include the phenomena of soft gluon interference. Using data from CM energies between 14 and 91 GeV, we study the dependence of the inclusive momentum distribution on the centre of momentum energy. We find that the analytical formulae describe the data over the entire energy range. Both the momentum distribution at a fixed energy and the change with energy are described by QCD shower Monte Carlo's which include either coherent gluon branchings or string fragmentation. Simple incoherent models with independent fragmentation fail to reproduce the energy dependence and momentum spectra.
Statistical errors only. Overall systematic error of 5%.
Using the ARGUS detector at the e + e − storage ring DORIS II at DESY, we have observed production of the charmed-strange baryon Ξ c + and its neutral isospin partner, the Ξ c 0 . The Ξ c + was reconstructed in the final state Ξ − π + π + , while the Ξ c 0 was seen in decay to Ξ − π + and Ξ − π + π + π − . The average Ξ c fragmentation spectrum has been determined, as well as the production cross section times branching ratio for each decay mode. The charged and neutral masses were measured to be 2465.1 ± 3.6 ± 1.9 MeV/ c 2 and 2472.1 ± 2.7 ± 1.6 MeV/ c 2 respectively, corresponding to a mass-splitting, M ( Ξ c + ) − M ( Ξ c 0 ), of −7.0±4.5±2.2 MeV/ c 2 .
Cross sections times branching ratios for $\Xi_c^0$ and $\Xi_c^+$ production at $E_{\mathrm{cms}} = 10.5$ GeV and $x_p > 0.5$.
Cross sections times branching ratios for $\Xi_c^0$ and $\Xi_c^+$ production at $E_{\mathrm{cms}} = 10.5$ GeV and all $x_p$.
Data requested from authors.
We present the charged-particle multiplicity distributions for e+e− annihilation at center-of-mass energies from 50 to 61.4 GeV. The results are based on a data sample corresponding to a total integrated luminosity of 30 pb−1 obtained with the AMY detector at the KEK storage ring TRISTAN. The charged-particle multiplicity distributions deviate significantly from the modified Poisson and pair Poisson distributions, but follow Koba-Nielsen-Olesen scaling and are well reproduced by the LUND parton-shower model.
Fully corrected charged particle multiplicity distributions. Errors for n=2 and 4 are systematic only since these were derived using the LUND 6.3 Monte Carlo normalized to the observations at higher n values.
No description provided.
The relative production ratio of 3-jet events to the total number of hadronic events was studied in e + e − annihilations at centre-of-mass energies between 54 and 61.4 GeV. The QCD scale parameter has been determined to be Λ MS =254 −47 +55 ±56 MeV on the basis of a QCD cascade with the next-to-leading logarithmic approximation.
Data are uncorrected for initial radiation, detector effects, and quark hadronization.
LAMBDA-MSBAR determined from the 3-jet ratio.
Search for baryon pairs production ine+e− annihilation at\(\sqrt s= 2386 MeV\) is reported. The data relate to a luminosity of 161 nb−1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe+e− annihilation into\(\Lambda \bar \Lambda \) and ofe+e−→\(p\bar p\) at this energy are presented. First observation of a goode+e−→\(n\bar n\) candidate is reported and upper limits are given fore+e−→\(n\bar n, \Lambda \bar \sum ^0+ c.c.\) and\(\Sigma ^0 \bar \Sigma ^0 \).
No description provided.
No description provided.
No description provided.
We present measurements of global event shape distributions in the hadronic decays of theZ0. The data sample, corresponding to an integrated luminosity of about 1.3 pb−1, was collected with the OPAL detector at LEP. Most of the experimental distributions we present are unfolded for the finite acceptance and resolution of the OPAL detector. Through comparison with our unfolded data, we tune the parameter values of several Monte Carlo computer programs which simulate perturbative QCD and the hadronization of partons. Jetset version 7.2, Herwig version 3.4 and Ariadne version 3.1 all provide good descriptions of the experimental distributions. They in addition describe lower energy data with the parameter values adjusted at theZ0 energy. A complete second order matrix element Monte Carlo program with a modified perturbation scale is also compared to our 91 GeV data and its parameter values are adjusted. We obtained an unfolded value for the mean charged multiplicity of 21.28±0.04±0.84, where the first error is statistical and the second is systematic.
Corrected Thrust distribution.
Corrected Major distribution.
Corrected Minor distribution.
None
Ratio per multihadron event for continuum data.
Ratio per multihadron event for continuum data.
Ratio per multihadron event for continuum data.
The reactionγγ→π+π−π+π− has been studied with the ARGUS detector. The rate in the invariant mass region below 1.8 GeV/c2 is found to be largely due toρ0ρ0 production. A spin-parity analysis shows a dominance of the partial wave (JP,Jz)=(2+, 2) with a small admixture fromJP=0+. The contribution of negative parity states is consistent with zero. The large ratio of cross sectionsσ(γγ→ρ0ρ0)/σ(γγ→ρ+ρ−)≃4, and the dominance of theJP=2+ wave in the reactionγγ→ρ0ρ0 is a signature consistent with the production of an exotic (I=2) resonance.
No description provided.
Statistical errors only.. Cross-section assuming phase-space distribution, as obtained by a 7 parameter fit.
Statistical errors only.. Cross-section assuming phase-space distribution, as obtained by a 7 parameter fit.
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