The forward-backward asymmetry of bottom quarks is measured with statistics of approximately 80 000 hadronic Z 0 decays produced in e + e − collisions at a centre of mass energy of √ s ≈ M z . The tagging of b quark events has been performed using the semileptonic decay channel b→X+ μ . Because the asymmetry depends on the weak coupling, this leads to a precise measurement of the electroweak mixing angle sin 2 θ w . The experimental result is A FB b = 0.115±0.043(stat.)±0.013(syst.). After correcting the value for the B 0 B 0 mixing this becomes A FB b =0.161±0.060(stat.)±0.021(syst.) corresponding to sin 2 θ W MS =0.221±0.011( stat. )±0.004( syst. ) .
Experimentally measured asymmetry.
Asymmetry corrected for mixing using mixing parameter 0.143 +- 0.023.
SIN2TW measured in MSBAR scheme.
Particle production in proton-induced reactions at 14.6 GeV/c on Be, Al, Cu, and Au targets has been systematically studied using the E-802 spectrometer at the BNL-Alternating Gradient Synchrotron. Particles are measured in the angular range from 5° to 58° and identified up to momenta of 5, 3.5, and 8 GeV/c for pions, kaons, and protons, respectively. Mechanisms for particle production are discussed in comparison with heavy-ion-induced reactions at the same incident energy per nucleon.
No description provided.
No description provided.
No description provided.
The L3 detector at LEP has been used to determine the number of light neutrino families by measuring the cross section of single photon even in e + e − collisions at energies near the Z 0 resonance. We have observed 61 single photon candidates with more than 1.5 GeV of deposited energy in the barrel electromagnetic calorimeter, for a total integrated luminosity of 3.0 pb −1 . From a likelihood fir to the single photon cross sections, we determin N ν =3.24 ± 0.46 ( statistical ) ±0.22 ( systematic ).
Corrected single photon cross sections. Errors represent 68 pct CL intervals and take into account the background fluctuations.
An analysis of the production of strange particles from the decays of the Z 0 boson into multihadronic final states is presented. The analysis is based on about 90 000 selected hadronic Z 0 decays collected by the DELPHI detector at LEP in 1990. K s 0 , K ∗± , Λ( Λ ) and Ξ − ( Ξ + ) have been identified by their characteristic decays. The measured production cross sections are compared with predictions of the Lund Monte Carlo tuned to data at PEP/PETRA energies.
No description provided.
No description provided.
No description provided.
The charged particle multiplicity distribution of hadronic Z decays was measured on the peak of the Z resonance using the ALEPH detector at LEP. Using a model independent unfolding procedure the distribution was found to have a mean 〈 n 〉=20.85±0.24 and a dispersion D =6.34±0.12. Comparison with lower energy data supports the KNO scaling hypothesis in the energy range s =29−91.25 GeV. At s =91.25 GeV the shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production. The same model also successfully describes the energy dependence of the mean and width of the multiplicity distribution. A next-to-leading order QCD prediction in the framework of the modified leading-log approximation and local parton-hadron duality is found to fit the energy dependence of the mean but not the width of the charged multiplicity distribution, indicating that the width of the multiplicity distribution is a sensitive probe for higher order QCD or non-perturbative effects.
Unfolded charged particle multiplicity distribution. The entry for N=2 is from the LUND 7.2 parton shower model.
Leading moments of the charged particle multiplicity. R2 is the second binomial moment given by MEAN(MULT(MULT-1))/(MEAN(MULT))**2.
Antiproton production cross sections have been measured for minimum bias and central Si+Al and Si+Au collisions at 14.6 A GeV c . The data presented cover the range of transverse momentum from 0.3 to 1.2 GeV c and lab rapidities from 1.1 to 1.7 units. The relative p π − and p K − yields are found to be the smallest for the heaviest system measured, central Si+Au collisions. For these collisions, the p π − ratio, determined from integrated yields for 1.1⩽ y ⩽1.7, is (0.84±0.07)×10 −3 . In the same rapidity interval, the average antiproton inverse m ⊥ slope is 141±14 MeV for central Si+Al and central Si+Au collisions.
Definition of the CENTRAL and MINIMUM BIAS events see text.
Definition of the CENTRAL and MINIMUM BIAS events see text.
We have measured the ratio of the strong coupling constants α s for bottom quarks and light quarks at the Z 0 resonance, in order to test the flavour independence of the strong interaction. The coupling strength α s has been determined from the fraction of events with three jets, measured for a sample of all hardronic events, and for inclusive muon and electron events. The b purity is evaluated to be 22% for the first data set and 87% for the inclusive lepton sample. We find α s ( b ) α s ( udsc ) =1.00± 0.05 ( stat. )±0.06 ( syst. ) .
No description provided.
None
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The properties of theZ resonance are measured on the basis of 190 000Z decays into fermion pairs collected with the ALEPH detector at LEP. Assuming lepton universality,Mz=(91.182±0.009exp±0.020L∶P) GeV,ГZ=(2484±17) MeV, σhad0=(41.44±0.36) nb, andГjad/Гℓℓ=21.00±0.20. The corresponding number of light neutrino species is 2.97±0.07. The forward-back-ward asymmetry in leptonic decays is used to determine the ratio of vector to axial-vector coupling constants of leptons:gv2(MZ2)/gA2(MZ2)=0.0072±0.0027. Combining these results with ALEPH results on quark charge and\(b\bar b\) asymmetries, and τ polarization, sin2θW(MZ2). In the contex of the Minimal Standard Model, limits are placed on the top-quark mass.
Statistical errors only.
No description provided.
No description provided.
The total and differential cross-sections for the reaction e + e − → γγ ( γ ) are measured at centre of mass energies around 91 GeV using an integrated luminosity of 4.7 pb −1 . The aggreement with QED prediction is good. Consequently there is no evidence for non-standard channels which would have the same experimental signature. The lower limits on the QED cuttoff parameters are Λ + > 113 GeV and Λ − > 95 GeV. An upper limit on the effective coupling between a possible excited electron and the gamma is derived. At 95% confidence level the branching ratios for Z 0 decay into π 0 γ, ηψ and γγγ are below 1.5 × 10 −4 , 2.8 × 10 −4 and 1.4 × 10 −4 respectively.
Radiative effects are subtracted.
Radiative effects subtracted.
Forum