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The muon detector of the HERA-B experiment at DESY (Hamburg, Germany) is a gaseous detector that provides muon identification in a high-rate environment. Pairs of muons with an invariant mass in the region of the J//spl psi/, meson ensure the first-level trigger for the experiment. Three different types of gas proportional chambers are employed: tube, pad, and pixel. The muon detector is fully installed and has been continuously running since November 1999. A clear signal for J//spl psi//spl rarr//spl mu//spl mu/, is reconstructed from data taken during the commissioning run. Design of the muon system as well as experience gained with detector commissioning are presented in this paper. The severe radiation environment of the HERA-B experiment leads to a maximum charge deposit on a wire, within the muon detector, of 200 mC/cm per year. We report recent results of aging studies performed by irradiating proportional wire chambers filled with Ar/CF/sub 4/,/CK and Ar/CF/sub 4//CO/sub 2/ mixtures under various conditions. These results show that aging rates obtained by irradiating a small region of the wire with a radioactive source cannot be extrapolated to the irradiation of large areas in an environment of hadronic interactions. Our experience shows that the aging rate depends not only on the total collected charge but also on the mode of operation and area of irradiation.

We have implemented a cost-effective design for the readout electronics of both the anode wires and the cathode pads of large area proportional wire chambers for the HERA-B muon system based on the ASD-08 integrated circuit. To control and monitor the large number of readout channels, we have built a distributed control system based on Philips Semiconductors' I2C bus and microcontrollers. To date we have installed about 10800 channels of muon chambers and electronics. The average single channel noise occupancy is less than 10**-5, and the detectors have been operated with target interaction rates as high as 70 MHz., Comment: 9 pages, 13 figures; submitted to IEEE Transactions on Nuclear Science; to appear in Conference Record of 1998 IEEE NSS in Toronto

The HERA-B experiment is designed to study beauty particle production and decay using the HERA 920 GeV proton beam interactions with an internal target. The Muon detector provides identification for muons having momenta greater than 5 GeV/c and triggering on the muon pair from J/ψ decay. Three different chamber types are employed for operation in a high-rate environment. The overall design, performance and current status are discussed.

Results of experimental studies of the performance of the uranium calorimeter with gas sampling detectors are presented. There is further evidence showing the importance of the contribution of the neutron component of a hadronic shower to the detected signal. The response and the resolution of the uranium calorimeter are measured in the momentum range 0.3–6.0 GeV/ c for the different incident particles and different gases that are used in the detectors. For a calorimeter structure with double-gas-detector layers, the correlation between signals from two calorimeters formed by chambers filled with different gas mixtures is measured. The topics that are relevant to the performance of the L3 uranium-gas sampling calorimeter - such as its operation in the magnetic field, the energy dependence of muon response, the uranium noise, as well as the electronics optimization - are discussed.