MEASUREMENT OF THE PROCESSES e+ e- ---> e+ e- AND e+ e- ---> gamma gamma AT PETRA

Cross sections for the reactionse + e −→e + e − (Bhabha scattering) ande + e −→γγ are measured for center-of-mass (c.m.) energies s√ between 12.0 and 34.6 GeV. The results agree with the predictions of Quantum Electrodynamics (QED) and the cut-off parameters are determined. From Bhabha scattering at the highest energy, ⟨s√⟩=34.6GeV , the 1 δ limits 0.12<sin2 ϑ w <0.38 are obtained for the weak mixing angle. The higher order (α3) QED processese + e −→e + e −γ ande + e −→γγγ are also studied and are found to agree with the α3 QED predictions. A search for excited electrons is carried out by investigating the (e ±γ) invariant mass distribution in the reactione + e −→e + e −γ

Tests of the standard model in leptonic reactions at PETRA energies

An analysis of the three leptonic reactionse + e −→e + e −,μ + μ − andτ + τ − over a wide range of energy, 12<s√<46.78GeV is presented. The data were obtained with the JADE detector at thee + e − storage ring PETRA. They are compared to predictions of electroweak theories, in particular the standard model. For the total cross-sections of all three reactions and for the differential cross-section of Bhabha scattering no deviation from QED is found over the entire energy range. The differential cross-sections of μ and τ pairs at high energies show the angular asymmetry predicted by electroweak interference. The axial-vector and vector weak coupling constant, sin2 θ W andM Z are determined and compared to other measurements. Finally, limits on deviations from the standard model are given

Test of QCD analytic predictions for the multiplicity ratio between gluon and quark jets

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Jets and QCD: A Historical Review of the Discovery of the Quark and Gluon Jets and its Impact on QCD

The observation of quark and gluon jets has played a crucial role in establishing Quantum Chromodynamics [QCD] as the theory of the strong interactions within the Standard Model of particle physics. The jets, narrowly collimated bundles of hadrons, reflect configurations of quarks and gluons at short distances. Thus, by analysing energy and angular distributions of the jets experimentally, the properties of the basic constituents of matter and the strong forces acting between them can be explored. In this review, which is primarily a description of the discovery of the quark and gluon jets and the impact of their observation on Quantum Chromodynamics, we elaborate, in particular, the role of the gluons as the carriers of the strong force. Focusing on these basic points, jets in e+e− collisions will be in the foreground of the discussion and we will concentrate on the theory that was contemporary with the relevant experiments at the electron-positron colliders. In addition we will delineate the role of jets as tools for exploring other particle aspects in ep and \hbox{$pp/p\bar{p}$} collisions  −  quark and gluon densities in protons, measurements of the QCD coupling, fundamental 2-2 quark/gluon scattering processes, but also the impact of jet decays of top quarks, and W ± , Z bosons on the electroweak sector. The presentation to a large extent is formulated in a non-technical language with the intent to recall the significant steps historically and convey the significance of this field also to communities beyond high energy physics