Design and tests of the z-coordinate drift chamber system for the opal central detector at LEP

A system of drift chambers has been designed to make high resolution measurements of the z-coordinates of charged tracks at the outer radius of the OPAL central detector at LEP. The unit module of this detector is a 25 cm drift length bidirectional cell with six sense wires in a thin 50 cm wide by 29 mm high drift slot. Tests indicate that the chamber has a wide and stable electric field operating range and its performance is unaffected by small misalignments between the drift electric field and an external magnetic field. The drift cell was found to have uniform acceptance up to its geometrical boundaries, and the z-resolution for beam tracks normal to the chamber was measured to be in the range of 40–175 μm.     

Large diameter radial semiconductor drift chambers for low noise radiation detection

A semiconductor drift chamber with cylindrical symmetry has been investigated theoretically for its suitability as a low noise radiation detector. The signal/noise of a silicon drift chamber at room temperature is likely to be determined by the detector dark current and the drift chamber should be superior in performance to a conventional pn junction detector of equivalent dimensions. A device of 48 mm diameter and 300 μm thickness is predicted to be capable of an energy resolution of less than 5 keV fwhm at 300 K. This is about seven times better than that predicted for its conventional counterpart.     

A simultaneous hit finding and timing method for pulse shape analysis of drift chamber signals

An algorithm for the analysis of the digitized signal waveform of drift chamber pulses is described which yields a good multihit resolution and an accurate drift time determination with little processing time. The method has been tested and evaluated with measured pulse shapes from the full size prototype of the OPAL central detector which were digitized by 100 MHz FADCs.     

Charge division in a small proportional chamber constructed with aluminized mylar tubes

A tracking detector composed of aluminized mylar drift tubes is under development for the Fermilab experiment 760. A prototype chamber has been constructed. Results on the longitudinal coordinate determined by charge division are given. Spatial resolution values below 2 mm (rms) were found, corresponding to <1% of the chamber length. Results on chamber ageing are also discussed.     

Track fitting in the OPAL vertex detector with stereo wires

The geometry of the vertex chamber for the OPAL detector at LEP is reviewed and expressions for the coordinates of the hits are given in terms of the measured drift distance and z-coordinate. The tracks are fitted by a procedure based on the Lagrange multipliers method. The increase in the accuracy of the fit due to the use of the stereo wires is discussed.     

A sectorised ionisation chamber: The MEΩ detection system

A detection system consisting of a sectorised ionisation chamber coupled with parallel plate avalanche counters and plastic scintillator telescopes is described. The active area is 120 cm² corresponding to angular apertures of 30° in plane and ±1° out of plane (experimental configuration). The sectorisation allows both an improved counting rate capability of the detector and a great versatility in its use. The addition of plastic scintillators in the rear part of the detector permits to enlarge the dynamic range of the charge measurement up to energetic light charged particles. A radial grid (θ grid) gives a precise in plane localisation (0.1°) while drift time measurement allows the determination of the out of plane coordinate. The energy resolution of the ionisation chamber is 1% for 120 MeV ³²S and the energy loss resolution is 3–5% depending on the anode section considered. The charge resolution is therefore better than 1.8%.     

Liquid argon ionization drift chamber with coordinate resolution of σx ∼ 20 μm

Estimates of the spatial resolution of a liquid argon ionization drift chamber are presented in the paper. The results obtained exhibit a possibility to construct a simple coordinate detector with a spatial resolution of σ_x = 20 μm and a two-track separation better than 1 mm, while good energy resolution characteristics for the LA detector are being conserved. The calculations were performed for an ionization cylindrical chamber with the cathode and anode diameter 4 cm and 0.1 mm, respectively. The fluctuations of ionization losses in thin samples and the noise jitter after shaping were taken into account in the analysis.     

Radial wire drift chambers for CDF forward tracking

We describe the design, construction, and operating experience of unique drift chambers with radially strung wires for the Collider Detector of Fermilab (CDF) [1] which cover forward and backward cone angles between 2° and 10°, and 170° and 178°. The chambers are capable of operating in our high rate and high track multiplicity environment with excellent multitrack resolution of 2–3 mm and high tracking accuracy of 140 μm per wire. Results from the recent running experience will be presented.     

A three dimensionally position sensitive large area detector

A large area detector consisting of a parallel plate avalanche counter (PPAC) and a trapezohedral ionization chamber (TIC) is described. Its active area is 184 cm². The time resolution of the PPAC is 175 ps. The energy resolution of the TIC is 0.4%, the energy loss resolution 2.8%, the nuclear charge resolution 2.3%. The TIC is position sensitive in three dimensions. The position x is measured via a saw-tooth anode with a resolution of 0.7 mm; the drift time coordinate shows a resolution of δy ? mm. The range z is determined by a new technique, a graded density Frisch grid. It enlarges the dynamic range of the charge measurement down to the Bragg maximum at E/A ～ 1 MeV. The resolution is δZ/Z ? 3.5%     

Signal rise times and energy resolution in radial semiconductor drift chambers

The risetimes expected in a semiconductor drift chamber (SDC) incorporating a constant drift field component to the electric field have been calculated. The combined influence of systematic risetime broadening and the random broadening processes has been determined and applied to some hypothetical test cases. It is predicted that the resolution of a 50 mm diameter SDC at 300 K will be limited by straggle in the dead layer for alpha particle spectrometry. The same detector could also detect 10 keV X-rays with an anticipated σ of 1.4 keV, limited by the electronic noise.     

Apparatus for precise drift time change measurements by means of photoelectrons emitted from the cathode

A drift chamber which measures the drift time of photoelectrons emitted from the cathode surface by means of a UV laser pulse has been built. The chamber is used for monitoring the drift time changes in the muon chambers of the L3 detector at CERN due to changes of gas parameters with the accuracy of 0.1%. The construction and experiments to determine the accuracy and stability of the device are described.     

Test of a high resolution drift chamber prototype

The performance of a drift chamber prototype for a colliding beam vertex detector in a test beam at DESY is described. At one (two) atmosphere gas pressure a spatial resolution of 40 μm (30 μm) per wire for one cm drift length was achieved with a 100 MHz Flash-ADC system. An excellent double track resolution of better than 300 μm over the full drift length of 5 cm can be estimated.     

Tension measurement of 7.6 m drift tubes of the VENUS muon detector

A semiautomated tension measurement system was developed and constructed for 7.6 m long drift tubes of the VENUS detector at KEK. The system utilizes the wire vibration method and consists of a 400 G, 40 cm long dipole magnet and two CAMAC modules. The voltage and phase shift induced in an anode wire are measured to detect the resonance frequency of wire vibration when an alternating current is applied to the wire in a magnetic field. Eight wires in a module can be consecutively measured by a computer control. The reproducibility of data measured by the system was found to be excellent and the accuracy of the measurement was also found to be satisfactory. Tension data obtained for 800 wires of 70 μm in diameter have the mean value of 394.4 gw with the rms deviation of 7.2 gw for the intended wire tension of 400 gw.     

A simple drift chamber using double sense wire readout

A new simple high aspect ratio drift chamber is discussed. By using two central sense wires the left-right position ambiguity is resolved within just one detector plane.     

A drift chamber with variable drift velocity

A wedge-type drift chamber is planned to be used as part of the inner detector of the DELPHI experiment at the large electron-positron (LEP) collider at CERN. The chamber features drift velocities (carefully controlled) proportional to the total drift distance to facilitate triggering. The gas choice and its consequencea for calibration with and without magnetic field are discussed. Long-term stability and the effect of a magnetic field have been measured with a prototype chamber. Most tests reported here have been done with a laser beam with single wire accuracies below 20 μm. The single wire accuracy for measuring minimum ionizing particles was found to be 80 μm.     

A twin ionization chamber for fission fragment detection

A twin ionization chamber for fission fragment detection is described. The detector permits measurement of the two fission fragment kinetic energies in an advantageous 2×2π geometry with an energy resolution of <0.5 MeV. The fission fragment emission angle θ with respect to the symmetry axis of the chamber is measured with a resolution in cos θ of <0.05. The fission fragment nuclear charge distributions can be determined and a timing signal can be extracted which allows a determination of the instant of fission with a time jitter of <0.7 ns. A pulse pileup rejection technique was developed which reduces pulse pileup by more than a factor 30. The electronic treatment of the chamber pulses and the data handling procedures including several of the necessary corrections are described in detail.     

Cathode readout of limited streamer tubes with conductive plastic walls

The performance of cathode readout on the limited streamer drift tubes with conductive plastic wall was studied. Cathode strips were placed on the outside of tubes in parallel and perpendicular to the anode wires. It was found that conductive plastic walls broadened the induced charge distribution on the cathode strips perpendicular to the anode wire. Position resolution of 420–450 μm was obtained along the anode wire, and parallel strips were found to be useful to solve left-right ambiguities in the drift chamber readout.     

Parallel pulse processing for mercuric iodide gamma-ray detectors

Mercuric iodide, a high-Z, wide band-gap semiconductor material, is a room temperature gamma-ray detector. Poor hole transport properties limit the detector performance. By parallel pulse processing schemes we are exploring this problem and making corrections to enhance resolution. This yields interaction depth information which is used to estimate hole collection deficits. Deficit estimates are used as corrections to pulse height to enhance resolution, or to reject pulses from high-deficit regions. These techniques have been implemented by several schemes for filtering the pulses using off-the-shelf amplifiers and computer simulation of amplifiers on detectors from 1–3 mm thick. Hardware and simulated results are compared and improved spectral performance is discussed. A resolution better than 7% for correction and 2.5% for rejection of hole deficit is obtained.     

CDF central muon detector

Design, construction and performance characteristics of the streamer chambers for the central muon detector at CDF are described. A single hit TDC is used for measurements in the drift (azimuth) direction while charge division is used for measurements along the sense wire (pseudorapidity). The chambers operate in the limited streamer mode with a 50%/50% ratio of argon/ethane bubbled through ethanol. Measurements in a cosmic ray test stand, pion test beam and as part of the CDF detector indicate that an rms resolution of 250 μm in the drift direction and an rms resolution of 1.2 mm along the sense wire are attainable.     

Pulse shape simulation for drift chambers with long drift paths

A detailed Monte Carlo program for the simulation of drift chamber pulse shapes is described. It has been applied to the case of a jet chamber with drift paths up to 24 cm. Results on pulse shapes and corresponding spatial and double hit resolution are discussed and compared to recent measurements of the OPAL central detector jet chamber full size prototype and to measurements of a small 20-wire prototype, which was designed to study the pulse shapes generated by tracks in a magnetic field. Simulated pulse shapes and spatial resolutions agree well with the experimental data. Clustering, saturation and wire crosstalk are shown to be necessary ingredients in the simulation. A deterioration in resolution due to the influence of crosstalk signals is correctly reproduced, as well as the cancellation of this effect by a hardwired first and second neighbour crosstalk compensation. The simulation correctly describes the asymmetry in spatial resolution observed for tracks with positive or negative inclination against the wire plane when a magnetic field is present. The effect of saturation on double hit resolution is found to be small. The magnetic field is predicted to improve the double hit resolution.