E. Daubie

Performance of MSGC on electronically and ionically conductive substrata in various operational conditions

Abstract Recent measurements realized with Microstrip Gas Chambers (MSGC) manufactured on glass substrata in a range of bulk resistivity are presented. Chambers made on electronically conductive supports with resistivity of 10 9 ω cm and gold strips show a stable behaviour during long term irradiation up to an accumulated charge of 130 mC/cm of strip when operated in an argon-dimethylether (DME) mixture. Similar measurements realised with argon-methane show instead a fast degradation of gain already at collected charge of around 5 mC/cm. Further investigation of MSGC performance with different Ar-DME compositions show that the larger stable gain can be achieved with a 50-50 mixture. We present also results of beam runs performed with MSGC manufactured on Hoya SL glass with an anode to cathode distance of 200 μm and a 2 mm gas layer. The dependence of efficiency and spatial resolution on the incidence angle of track was measured with argon-DME and xenon-DME gas mixtures; for minimum ionizing particles perpendicular to the chambers (0°) the spatial resolution for Xe gas mixture is 65 μm rms and the efficiency 98%. For incidence angles up to 10° a small degradation of both parameters was observed.

Drift chambers operated in the limited streamer mode

Abstract Successful operation of a drift chamber with 10 cm drift in the limited streamer mode is demonstrated. Good results were obtained with a 50-50 argon-isobutane gas mixture. A preliminary search for alternative gas mixtures avoiding the hydrocarbon quencher component is described.

The MICROMEGEM detector

Abstract This article introduces the MICROMEGEM detector, a position-sensitive proportional gas counter produced using advanced Printed Circuit Board (PCB) technology. The detector is equipped with a Gas Electron Multiplier (GEM) foil placed 50 μm above a plane of pick-up strips. The GEM produces a first gas amplification which is extended below the GEM foil by applying a strong electric field between the strips and the lower electrode of the GEM. The array of strips is used for read-out to obtain 1-D positional information. We present results on the gas gain, the energy resolution and the rate capability. The behaviour in an intense beam of 300 MeV /c pions in presence of heavily ionizing particles has also been investigated.

Drift chambers with delay line readout operated in the limited streamer mode

Abstract This report presents the performance of drift chambers operated in the limited streamer mode with 9.4 cm maximum drift distance and position sensing along the 4.35 m long anode wire through delay line timing. Using only three timing channels a position resolution of 1×3 mm 2 is obtained over a detector surface of 19×435 cm 2 . In this contribution, the emphasis is mainly put on the performance of the delay line and on the drift behaviour in streamer mode using safe gas mixtures.

The forward muon detector of the DELPHI experiment at LEP

Abstract The layout and construction of the muon drift chambers equipping the end caps of the DELPHI detector are described. The performance of this forward muon detection system, determined from cosmic ray tests and data collected during the first year of LEP operation, is presented.

Performance of the delay lines of the delphi forward muon chambers

Abstract This report presents the performance of 4.35 m long delay lines used for position sensing along the anodes of drift chambers operated in the limited-streamer mode. Using only the time difference between the signals at the two ends of the delay line, a spatial resolution ranging from 1.5 to 2.5 mm is obtained, equivalent to 0.06% of the 4.35 m length of the line. The linearity of the time-to-distance relation is also studied.

Performance improvement of streamer drift chambers by the addition of organic vapours to the gas mixture

Abstract The stability of operation and the detection efficiency of drift chambers running in streamer mode are substantially improved when adding a few percent of organic vapour to gas mixtures composed of Ar, CO2 and iC4H10.

Determination of 55-155-155-1in second order QCD from hadronic Z decays

Distributions of event shape variables obtained from 120600 hadronicZ decays measured with the DELPHI detector are compared to the predictions of QCD based event generators. Values of the strong coupling constant αs are derived as a function of the renormalization scale from a quantitative analysis of eight hadronic distributions. The final result, αs(MZ), is based on second order perturbation theory and uses two hadronization corrections, one computed with a parton shower model and the other with a QCD matrix element model.

Measurement of the partial width of the Z0 into b {Mathematical expression} final states using their semi-leptonic decays

AbstractThe spectra of prompt electrons and muons from the semi-leptonic decays of heavy hadrons produced inZ0 decays have been used to measure the coupling of theZ0 tob quarks weighted by theB hadrons mean semi-leptonic branching fraction, giving a value: