A new drift chamber concept with a special charge-sampling geometry, pulse shaping electronics and a 100 MHz flash ADC readout was for the first time operated in a colliding e+ e− beam environment. The detector formed part of the MARK J experiment at PETRA (DESY) during the last year before its final shutdown in November 1986. Operated with a CO2/i-C4H10 gas mixture at 1.9 bar, an intrinsic resolution of 40 μm for Bhabha events has been achieved.

In a Time Expansion Chamber two high resolution drift volumes on both sides of a small detection gap are separated from the gap by a fine grid wire plane. The charge asymmetry induced on the grid wires in the vicinity of an anode is used to resolve the right-left ambiguity. It is the only method which is fast enough for a first level trigger and which does not deteriorate the necessary field homogeneity.

A high-resolution drift chamber based on the time expansion principle has been built as a vertex detector for the Mark J experiment at DESY. The chamber design and the associated control and readout system are described. Results on chamber performance obtained from test beam measurements and first results from running at PETRA are reported.

The Mark J Collaboration at the DESY e+e− collider PETRA presents results on the electroweak reactions e+e−→μ+μ−τ+τ−,μ+μ−γ, and e+e−μ+μ−. The c.m. energy range is 12 to 46.78 GeV. In the μ+μ− and τ+τ− channels the total cross sections and the forward-backward asymmetries are reported and compared with other experiments. The results are in excellent agreement with the standard model. The weak-neutral-current vector and axial-vector coupling constants are determined. The values for muons and τ's are compatible with universality and with the predictions of the standard model. In the μ+μ−γ channel, all measured distributions, including the forward-backward muon asymmetry, are in excellent agreement with the electroweak theory. Our data on the two-photon process, e+e−μ+μ−, agrees with QED to order α4 over the entire energy range and the Q2 range from 0.7 to 166 GeV2.Received 29 April 1988DOI:https://doi.org/10.1103/PhysRevD.38.2665©1988 American Physical Society

The design and results from a beam test for a small vertex detector, now installed in the DESY MARK J experiment, are presented. The concept of this drift chamber is based on the time expansion principle with readout planes inclined to solve the left-right ambiguity. A spatial resolution of 35 μm, varying weakly as a function of drift length and azimuthal angle, has been achieved.

A study of τ-lepton production in the CMS energy region from 14 to 46.8 GeV at PETRA is reported. The cross section, the decay branching ratio into μνν, and the electroweak parameters are determined with a total integrated luminosity of 115 pb−1.

The strong interaction coupling constant αs has been measured with a new method, the planar triple energy correlation in the reaction e+e- → hadrons at center-of-mass energies ranging from 14 GeV to 46.78 GeV. A complete second-order perturbative QCD calculation was used. ΛMS = 110 ± 30 −55+70 MeV is found.

We describe a fast and economical CAMAC auxiliary crate controller (ACC 9445) based on Fairchild's F9445 16-bit microprocessor. Design and performance as well as examples of applications are given.

The minimal model based on spontaneously broken supergravity predicts upper bounds on the mass of a neutral scalar Higgs particle. It is shown that these bounds are very restrictive if the mass of the top quark is less than 50 GeV. For a top quark mass of 30 (40) GeV the upper bound on the light Higgs is given by 11 (24) GeV respectively.