Z. Zheng

The Outer Tracker detector of the HERA-B experiment—Part I: Detector

Abstract The HERA-B Outer Tracker is a large system of planar drift chambers with about 113xa0000 read-out channels. Its inner part has been designed to be exposed to a particle flux of up to 2 × 10 5 cm - 2 s - 1 , thus coping with conditions similar to those expected for future hadron collider experiments. Thirteen superlayers, each consisting of two individual chambers, have been assembled and installed in the experiment. The stereo layers inside each chamber are composed of honeycomb drift tube modules with 5 and 10 mm diameter cells. Chamber aging is prevented by coating the cathode foils with thin layers of copper and gold, together with a proper drift gas choice. Longitudinal wire segmentation is used to limit the occupancy in the most irradiated detector regions to about 20%. The production of 978 modules was distributed among six different laboratories and took 15 months. For all materials in the fiducial region of the detector good compromises of stability versus thickness were found. A closed-loop gas system supplies the Ar/CF 4 /CO 2 gas mixture to all chambers. The successful operation of the HERA-B Outer Tracker shows that a large tracker can be efficiently built and safely operated under huge radiation load at a hadron collider.

The Outer Tracker detector of the HERA-B experiment. Part II: Front-end electronics

The HERA-B Outer Tracker is a large detector with 112674 drift chamber channels. It is exposed to a particle flux of up to 2x10^5/cm^2/s thus coping with conditions similar to those expected for the LHC experiments. The front-end readout system, based on the ASD-8 chip and a customized TDC chip, is designed to fulfil the requirements on low noise, high sensitivity, rate tolerance, and high integration density. The TDC system is based on an ASIC which digitizes the time in bins of about 0.5 ns within a total of 256 bins. The chip also comprises a pipeline to store data from 128 events which is required for a deadtime-free trigger and data acquisition system. We report on the development, installation, and commissioning of the front-end electronics, including the grounding and noise suppression schemes, and discuss its performance in the HERA-B experiment.

Aging studies for the large honeycomb drift tube system of the Outer Tracker of HERA-B

Abstract The HERA-B Outer Tracker consists of drift tubes folded from polycarbonate foil and is operated with Ar/CF4/CO2 as drift gas. The detector has to stand radiation levels which are similar to LHC conditions. The first prototypes exposed to radiation in HERA-B suffered severe radiation damage due to the development of self-sustaining currents (Malter effect). In a subsequent extended R&D program major changes to the original concept for the drift tubes (surface conductivity, drift gas, production materials) have been developed and validated for use in harsh radiation environments. In the test program various aging effects (such as Malter currents, gain loss due to anode aging and etching of the anode gold surface) were observed, and cures by tuning of operation parameters were developed.

The outer tracker detector of the HERA-B experiment. Part III: Operation and performance

Abstract In this paper we describe the operation and performance of the HERA-B Outer Tracker, a 112xa0674 channel system of planar drift tube layers. The performance of the HERA-B Outer Tracker system fullfilled all requirements for stable and efficient operation in a hadronic environment, thus confirming the adequacy of the honeycomb drift tube technology and of the front-end readout system. The detector was stably operated with a gas gain of 3 × 10 4 in an Ar / CF 4 / CO 2 (65:35:5) gas mixture, yielding a good efficiency for triggering and track reconstruction, larger than 95% for tracks with momenta above 5 GeV / c . The hit resolution of the drift cells was 300– 320 μ m and the relative momentum resolution can be described as: σ ( p ) / p [ % ] = ( 1.61 ± 0.02 ) + ( 0.0051 ± 0.0006 ) · p [ GeV / c ] . At the end of the HERA-B running no aging effects in the Outer Tracker cells were observed.