A precise measurement of the ratio R of the total cross section e+e−→hadrons to the pointlike cross section e+e−→μ+μ− at a center-of-mass energy of 29.0 GeV is presented. The data were taken with the upgraded Mark II detector at the SLAC storage ring PEP. The result is R=3.92±0.05±0.09. The luminosity has been determined with three independent luminosity monitors measuring Bhabha scattering at different angular intervals. Recent calculations of higher-order QED radiative corrections are used to estimate the systematic error due to missing higher-order radiative corrections in the Monte Carlo event generators.
No description provided.
We have studied the energy-energy correlation in e+e− annihilation into hadrons at √s =29 GeV using the Mark II detector at the SLAC storage ring PEP. We find to O(αs2) that αs=0.158±0.003±0.008 if hadronization is described by string fragmentation. Independent fragmentation schemes give αs=0.10–0.14, and give poor agreement with the data. A leading-log shower fragmentation model is found to describe the data well.
Correlation data from the original PEP-5 detector.
Correlation Asymmetry data from the original PEP-5 detector.
Correlation data from the upgraded detector.
We have measured the mass of the Z boson to be 91.14±0.12 GeV/c2, and its width to be 2.42−0.35+0.45 GeV. If we constrain the visible width to its standard-model value, we find the partial width to invisible decay modes to be 0.46±0.10 GeV, corresponding to 2.8±0.6 neutrino species, with a 95%-confidence-level upper limit of 3.9.
No description provided.
We have observed hadronic final states produced in the decays of Z bosons. In order to study the parton structure of these events, we compare the distributions in sphericity, thurst, aplanarity, and number of jets to the predictions of several QCD-based models and to data from lower energies. The data and models agree within the present statistical precision.
Corrected event shape distributions.
Corrected event shape distributions.
Corrected event shape distributions.
We have measured inclusive distributions for charged particles in hadronic decays of the Z boson. The variables chosen for study were charged-particle multiplicity, scaled momentum, and momenta transverse to the sphericity axes. The distributions have been corrected for detector effects and are compared with data from e+e− annihilation at lower energies and with the predictions of several QCD-based models. The data are in reasonable agreement with expectations.
Mean corrected charged particle multiplicity.
Corrected charged particle X distributions. Errors are statistical and systematic combined.
Corrected charged particle PTIN distributions. Errors are statistical and systematic combined.
Energy correlations have been measured with the MARK II detector at the PEP storage ring (Stanford Linear Accelerator Center) at c.m. energy of 29 GeV and are compared to first-order QCD predictions. Fragmentation processes are significant and limit the precision with which the first-order strong-coupling constant can be determined.
MEASUREMENT OF THE STRONG COUPLING CONSTANT.
We present a measurement of the cross section for hadron production by e+e− annihilation in the vicinity of the previously observed resonance near 3.77 GeV. The data are used to determine the parameters of the ψ(3770) resonance. The values found are: mass, 3764±5 MeV/c2, total width, 23.5±5 MeV, and partial width to electron pairs, 276±50 eV.
PEAK CROSS SECTION FOR D MESON PAIR PRODUCTION AT PSI(3770) RESONANCE. J/PSI, PSI(3684) AND CONTINUUM BACKGROUND (R=2.5) SUBTRACTED.
This final analysis of hadronic and leptonic cross-sections and of leptonic forward-backward asymmetries in e+e- collisions with the OPAL detector makes use of the full LEP1 data sample comprising 161 pb^-1 of integrated luminosity and 4.5 x 10^6 selected Z decays. An interpretation of the data in terms of contributions from pure Z exchange and from Z-gamma interference allows the parameters of the Z resonance to be determined in a model-independent way. Our results are in good agreement with lepton universality and consistent with the vector and axial-vector couplings predicted in the Standard Model. A fit to the complete dataset yields the fundamental Z resonance parameters: mZ = 91.1852 +- 0.0030 GeV, GZ = 2.4948 +- 0.0041 GeV, s0h = 41.501 +- 0.055 nb, Rl = 20.823 +- 0.044, and Afb0l = 0.0145 +- 0.0017. Transforming these parameters gives a measurement of the ratio between the decay width into invisible particles and the width to a single species of charged lepton, Ginv/Gl = 5.942 +- 0.027. Attributing the entire invisible width to neutrino decays and assuming the Standard Model couplings for neutrinos, this translates into a measurement of the effective number of light neutrino species, N_nu = 2.984 +- 0.013. Interpreting the data within the context of the Standard Model allows the mass of the top quark, mt = 162 +29-16 GeV, to be determined through its influence on radiative corrections. Alternatively, utilising the direct external measurement of mt as an additional constraint leads to a measurement of the strong coupling constant and the mass of the Higgs boson: alfa_s(mZ) = 0.127 +- 0.005 and mH = 390 +750-280 GeV.
The cross section for hadron production corrected to the simple kinematic acceptance region defined by SPRIME/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
The cross section for E+ E- production corrected to the simple kinematic acceptance region defined by ABS(COS(THETA(C=E-))) < 0.7 and THETA(C=ACOL) < 10 degrees. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross sectionat the central value of SQRT(S).
The cross section for mu+ mu- production corrected to the simple kinematic acceptance region defined by N = M(P=3_4)**2/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
Relative production rates of multijet hadronic final states of Z 0 boson decays, observed in e + e − annihilation around 91 GeV centre of mass energy, are presented. The data can be well described by analytic O( α s 2 ) QCD calculations and by QCD shower model calaculations with parameters as determined at lower energies. A first judgement of Λ MS and of the renormalization scale μ 2 in O( α s 2 ) QCD results in values similar to those obtained in the continuum of e + e − annihilations. Significant scaling violations are observed when the 3-jet fractions are compared to the corresponding results from smaller centre of mass energies. They can be interpreted as being entirely due tot the energy dependence of α s , as proposed by the nonabelian nature of QCD, The possibility of an energy independent coupling constant can be excluded with a significance of 5.7 standard deviations.
Data are corrected for final acceptance and resolution of the detector. No explicit corrections for hadronisation effects are applied.
We report on a measurement of the mass of the Z 0 boson, its total width, and its partial decay widths into hadrons and leptons. On the basis of 25 801 hadronic decays and 1999 decays into electrons, muons or taus, selected over eleven energy points between 88.28 GeV and 95.04 GeV, we obtain from a combined fit to hadrons and leptons a mass of M z =91.154±0.021 (exp)±0.030 (LEP) GeV, and a total width of Γ z =2.536±0.045 GeV. The errors on M z have been separated into the experimental error and the uncertainty due to the LEP beam energy. The measured leptonic partial widths are Γ ee =81.2±2.6 MeV, Γ μμ =82.6± 5.8 MeV, and Γ ττ =85.7±7.1 MeV, consistent with lepton universality. From a fit assuming lepton universality we obtain Γ ℓ + ℓ − = 81.9±2.0 MeV. The hadronic partial width is Γ had =1838±46 MeV. From the measured total and partial widths a model independent value for the invisible width is calculated to be Γ inv =453±44 MeV. The errors quoted include both the statistical and the systematic uncertainties.
Errors are statistical and point to point systematic luminosity error of 1 pct.
Measured values of e+ e- --> e+ e- cross section.
Corrected cross section. Corrections are for t-channel effects and loss of acollinear events near the boundary of the acceptance.