[en] The Mark-J detector is designed to measure and distinguish hadrons, electrons, neutral particles, and muons. It covers a solid angle of phi = 2π and theta = 9⁰ to 171⁰ (theta is the polar and phi is the azimuthal angle). The detector is symmetrical in both phi and theta directions. The physics objectives of this detector are: to measure the interference effects between weak and electromagnetic interactions by studying the charge asymmetry in the reaction e⁺e^- → μ⁺μ^- with an accuracy of 1%, to measure the total hadron production cross section, to study various quantum electrodynamic processes, to measure μe and μ hadron events and to study asymmetries associated with these events which can come from weak interaction effects, and to search for new quarks and heavy leptons

[en] This paper reports the results of a study of hadron production in e⁺e^- collisions at c.m. energies of 33, 35, and 35.8 GeV. Production of a new quark flavor has been sought. The measured values of the total cross section, the thrust distributions, and the study of inclusive muon production show no evidence for the production of a new charge-2/3e quark near threshold. In addition, during an energy scan in the region 29.9< or =√s< or =31.6 GeV, no hadron resonance indicating the existence of a bound state composed of charge-2/3e quarks has been found

[en] A study of hadron production in e⁺e^- collisions at the highest PETRA energies reached so far is reported. Production of a new quark flavor was sought at cms energies of 33, 35, and 35.8 GeV. The measured values of the total cross section, the thrust distributions, and the study of inclusive muon production show no evidence for the production of a new charge 2/3e quark near threshold. In addition, during an energy scan zn the region 29.9 less than or equal to √s less than or equal to 31.6 GeV, no hadron resonance indicting the existence of a bound state composed of charge 2/3e quarks was bound. 4 figures, 1 table

[en] During the initial running of PETRA at 27.4 GeV, we have measured the reaction e⁺e^- → hadrons using the MARK J detector. We find a value of R of 4.1 +- .5 (statistical) +- .7 (systematic). Events are analyzed in terms of thrust and sperocity. Overall, we find no evidence for a new threshold in hadron production up to the present energy. (orig.)

[en] This report reviews the experimental investigation of high energy e⁺e^- interactions by the MARK J collaboration at PETRA, the electron-positron colliding beam accelerator at DESY in Hamburg, Germany. The phyiscs objectives include studies of several purely electromagnetic processes and hadronic final states, which further our knowledge of the nature of the fundamental constituents and of their strong, electromagnetic and weak interactions. Before discussing the physics results, the main features and the principal components of the MARK J detector are discussed in terms of design, function, and performance. Several aspects of the on-line data collection and the off-line analysis are also outlined. Results are presented on tests of quantum electrodynamics using e⁺e^- → μ⁺μ^- and tau⁺tau^-, on the measurement of R, the ratio of the hadronic to the point-like muon pair cross section, on the search for new quark flavors, on the discovery of three jet events arising from the radiation of hard noncollinear gluons as predicted by quantum chromodynamics, and on the determination of the strong coupling constant αsub(s). (orig.)

[en] We report the measurement of the reaction e⁺ + e^- → hadronic jets at a center-of-mass energy √s = 30 GeV using the MARK-J detector at PETRA. By measuring the energy and angular distribution of both neutrals and charged particles we were able to isolate unambiguously the three-jet events in a kinematic region where the backgrounds from q anti q and phase space contributions and other processes are small. Various comparisons of the data with quantum chromodynamics were made. The relative yield of three-jet events and the shape distribution of the events enable us to determine αsub(s) = 0.23 +- 0.02 (statistical error) with a systematic error of +- 0.04. (orig.)

[en] We report on the measurement of the reaction e⁺e^- → e⁺e^- with a large--solid-angle electromagnetic shower detector at center-of-mass energies √s < 13 and 17 GeV. Comparison of our results with predictions of quantum electrodynamics shows excellent agreement in both the angular distribution and energy dependence. Values of cutoff parameters are also given

[en] We report the first measurement of the ratio R < (sigma/sub e/+/sub e/-atsub tsarrow-righttshadronsat)/(sigma/sub e/+/sub e/-atsub tsarrow-righttsmuat+/sub μ/-) (with negligible tau-lepton contribution) at a center-of-mass energy √s < 13 GeV and √s < 17 GeV, from the just finished electron-positron colliding-beam facility PETRA. The detector, MARK-J, has an approximately 4π solid angle and measures γ,e,μ, and charged and neutral hadrons simultaneously. Our results yield R (√s < 17 GeV) < 4.9 +- 0.6 (statistical) +- 0.7 (systematic error), and R (√s < 13 GeV) < 4.6 +- 0.5 (statistical) +- 0.7 (systematic error). The ratio R (√s < 17 GeV)/R (√s < 13 GeV) is 1.08 +- 0.18

[en] This paper reports on the first results of the study of e⁺e^- collisions at √s=27.4 GeV and √s=27.7 GeV at PETRA, using the 4π-sr electromagnetic and calorimetric detector MARK-J. We obtain an average R=sigma (e⁺e^- → hadrons)/sigma (e⁺e^- → μ⁺μ^-) =3.8 +- 0.3 (statistical) +- 0.6 (systematic) and a relative R=1.0 +- 0.2 between the two energies. The R values, the measured thrust distribution, and average spherocity show no evidence for the production of new quark flavors

[en] The authors report on the results of the study of e⁺e^- collisions at the highest PETRA energy of √s = 31.57 GeV, using the 4π sr, electromagnetic and calorimetric detector Mark J. Based on 88 hadron events, and an integrated luminosity of 243 nb^-1 they obtain R = sigma(e⁺e^- → hadrons)/sigma(e⁺e^-→μ⁺μ^-) = 4.0 +- 0.5 (statistical ) +- 0.6 (systematic). The R value, the measured thrust distribution and average spherocity show no evidence for the production of new quark flavors. (Auth.)