M. Rohde

New particle searches

Abstract PETRA, the e + e − collider, has operated at a maximum CM energy of 46.78 GeV. We update our previous results on new particle searches and set significantly better mass limits on some.

Experimental Study of Inclusive Muon Spectra at PETRA

The results of a high-statistics study of inclusive muon spectra at PETRA are reported. Improved mass limits have been obtained for heavy quarks, heavy leptons, and charged Higgs particles. It is shown that the fragmentation properties of b quarks and c quarks are different, with the mean fragmentation variables = 0.75 +- 0.03 +- 0.06, = 0.46 +- 0.02 +- 0.05 and the average semileptonic branching ratio for the B and C hadrons BR(B) = (10.5 +- 1.5 +- 1.3)%, BR(C) = (11.5 +- 1.0 +- 1.7)%.

Physics with high energy electron-positron colliding beams with the MARK J detector

Abstract 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 physics 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 − → e + e − , μ + μ − and τ + τ − , 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 α s .

Tests of quantum chromodynamics and a direct measurement of the strong coupling constant αs at √s=30 GeV

Abstract 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 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 αs = 0.23 ± 0.02 (statistical error) with a systematic error of ± 0.04.

PHOTOPRODUCTION OF NEUTRAL RHO MESONS.

We present results of measurements on photoproduction of ϱo mesons. Analysis of 105 measured π-pairs on protons in the energy region 2.6 − 6.8 GeV using various assumptions of rho production. indicates that dσ/dt(t = 0) decreases with increasing energy similar to πN scattering. Analysis of 106 measured π-pairs from 13 complex nuclei in a four-dimensional data matrix dσ/dΩdm(A.m.p.t⊥) with dimensions 13.20.6 and 20. yields precise information on nuclear density distributions determined by ϱ-production. We obtain for the Woods-Saxon radii R(A) = (1.12 ± 0.02) A13 fm. and using the vector-dominance model, σϱN = 26.7 ± 2.0 mb and γϱ2/4π = 0.57 ± 0.10.

Search for Charged Higgs, Scalar Taus, and a Test of Technicolor Models

Abstract We have used our measurements of final states from e+e− containing an isolated muon and a hadronic or electron shower to search for new spin 0 charged particles. We exclude (95% CL) a supersymmetric partner of the τ with a mass less than 14 GeV/c2. We obtain upper limits on the branching ratio to τvτ for charged Higgs particles or technipions with masses up to 14 GeV/c2. This disagrees with some technicolor model predictions.

UNIQUE SOLUTION FOR THE WEAK NEUTRAL CURRENT COUPLING-CONSTANTS IN PURELY LEPTONIC INTERACTIONS

Abstract By combining results from the MARK-J at PETRA on Bhabha scattering, μ + μ - and τ + τ - production with recent world data from neutrino-electron scattering experiments, we determine unique values for the leptonic weak neutral current coupling constants g V and g A in the framework of electroweak models containing a single Z 0 . In contrast to previous analyses, we only use data from purely leptonic interactions, and therefore avoid the inherent uncertainties resulting from the use of hadronic targets. From the MARK-J data alone in the context of the standard SU(2) ⊗ U (1) model of Glashow, Weinberg and Salam, we find sin 2 θ W =0.24±0.11.

Discovery of the new particle J

Abstract We present a description of an experiment carried out at the 30 GeV Alternating Gradient Synchrotron of the Brookhaven National Laboratory. The experiment used a high intensity slow extracted proton beam of between 10 10 and 2·10 12 protons per pulse and measured the e + e − mass spectrum from the reaction p + Be→e + e − + X. The results of this experiment shows the production of a new type of particle, J, which decays to e + e − with a width consistent with zero.

Virtual compton scattering at high energies

Abstract We have measured the large-angle asymmetrical electron-positron pair yields of the reaction γ + C → C + e + + e − and γ + Pd → Pd + e + +e − . As a means of determining the phase and magnitude of virtual Compton scattering amplitude at high energies (4–6 GeV) on complex nuclei. The first reaction was studied at an invariant pair mass m = m ϱ , the mass of ϱ O ; the second reaction over a mass interval 300 ⩽ m ⩽ 550 MeV.

Observation of coherent interference pattern between ϱ, ω decays

Abstract We report a high-statistics experiment measuring the structure of e+e− mass spectrum from photoproduction of ϱ- and ω-mesons. At 5.1 GeV, based on 4000 events, analysis of the spectra yields a ratio of vector-meson-photon coupling constants γ ω 2 σ ϱ N γ ϱ 2 σ ω N = 9.4 −1.6 +2.6 and a ϱ, ω production phase difference ϕωϱ = 41° ± 20°.