I. ten Have

Performance of the ALEPH Time Projection Chamber

Abstract The performance of the ALEPH Time Projection Chamber (TPC) has been studied using data taken during the LEP running periods in 1989 and 1990. After correction of residual distortions and optimisation of coordinate reconstruction algorithms, single coordinate resolutions of 173 μm in the azimuthal and 740 μm in the longitudinal direction are achieved. This results in a momentum resolution for the TPC of Δp / p 2 = 1.2 × 10 −3 (GeV/ c ) −1 . In combination with the ALEPH Inner Tracking Chamber (ITC), a total momentum resolution of Δp / p 2 = 0.8 × 10 −3 (GeV/ c ) −1 is obtained. With respect to particle identification, the detector achieves a resolution of 4.4% for the measurement of the ionisation energy loss.

GaAs solid state detectors for particle physics

Abstract We report on progress with Schottky diode and p-i-n diode GaAs detectors for minimum ionising particles. The radiation hardness and potential speed of simple diodes is shown to be more than competitive with silicon detector. A discussion is given of the present understanding of the charge transport mechanism in the detectors since it influences their charge collection efficiency. Early results from microstrip detectors are also described.

Heavy flavour production in large transverse momentum proton-antiproton collisions

We discuss the question of heavy flavour production in hard proton-antiproton collisions at the CERN SppS Collider. Our emphasis in this paper is mainly on the inclusive muon and dimuon cross sections recently measured by the UA1 collaboration. We estimate contributions to these final states from both strong and weak production processes using perturbative quantum chromodynamics, QCD. We find that large pt production of heavy flavours at the CERN collider energies is quantitatively well described by QCD. We present a detailed calculation to estimate the ratio of same-sign to opposite-sign dimuon production rate R(±±/+−) at the CERN pp collider, making use of the extensive data available on the production and decays of bottom and charmed hadrons in e+e− annihilation experiments. The calculated ratio R(±±/+−) is found to be significantly lower than the UA1 measurements. We argue that this ratio is theoretically well reproduced if one assumes substantial Bs0−Bs0 mixing. We determine the 2σ lower limit on the mixing probability rs ≡ Γ(Bs0 → l−νlX)/Γ(Bs0 → l+νlX) to be big than 0.14. In the standard model this gives a lower bound on the Kobayashi-Maskawa matrix element Vts which we estimate. Flavour correlations confirming Bs0 − Bs0 mixing in future experiments are emphasized.

Charge transport properties of undoped SI LEC GaAs solid-state detectors

Abstract The GaAs detectors for minimum ionizing particles fabricated with commercial undoped SI GaAs show good quality as minimum ionizing particle detectors. A discussion is given of the present understanding of the charge transport mechanism in the detectors since it influences their charge collection efficiency.

Gallium arsenide microstrip detectors for charged particles

Microstrip detectors have been constructed from gallium arsenide (GaAs) wafers made from undoped LEC (liquid-encapsulated Czochralski) semi-insulating substrate material. Tests were performed using minimum ionising particles to ascertain their properties as charged particle detectors. The results show that the devices work wellm, with good signal-to-noise ratio (typically 7). The effects of gamma ray and neutron irradiation have been studied and shown to be small up to levels exceeding 20 Mrad and 1014 n/cm2, respectively.

Gallium arsenide charged particle detectors; trapping effects

The progress on the development of gallium arsenide particle detectors is reviewed. The limitation to the performance is the presence of traps. Studies of the trap properties using α particle DLTS measurements and C-V measurements are described.

Gallium arsenide detectors for minimum ionizing particles

Abstract Progress on the development of GaAs solid state detectors is presented. 80% charge collection efficiency has been achieved, and double sided detectors with metal rectifying contacts have been tested. Measurements of capacitance and tests with SEM are giving more information on the behaviour of these devices.

First results from GaAs double-sided detectors

Abstract Preliminary results are presented on the performance of double-sided microstrip detectors using Schottky contacts on both sides of a semi-insulating (SI) GaAs substrate wafer, after exposure to 1014 neutrons cm−2 at the ISIS facility. A qualitative explanation of the device behaviour is given.

LEC SI-GaAs detectors for gamma rays

Abstract Detectors with a p-i-n structure based on Liquid Encapsulated Czochralski (LEC) grown Semi-Insulating (SI) GaAs have been fabricated. The current-voltage ( I – V ) characteristics and their response to γ-rays have been studied. Measurements of the peak charge collection efficiency (cce) have been compared with a model assuming a uniform electric field. The comparison indicates that this field is not uniform. The peak cce at 500 V is found to be 52% and 82% in 400 μm and 200 μm thick detectors respectively. The resolution of the 57 Co full energy peak is between 10% and 13% at 400 V.

GaAs solid state detectors for physics at the LHC

The authors report on progress with Schottky diode and p-i-n diode GaAs detectors for minimum ionizing particles. The radiation hardness and potential speed of simple diodes are shown to be more than competitive with silicon detectors. A discussion is given of the present understanding of the charge transport mechanism in the detectors as it influences their charge collection efficiency. Early results from microstrip detectors which are relevant for high radiation regions of Large Hadron Collider (LHC) detectors near the beam pipe and in the forward region are also described. The authors have established the ability of GaAs Schottky diode detectors to tolerate radiation loads at the level expected in more than one year of running at a radial distance of only a few cm from the intersection point of the proposed LHC collider at nominal luminosity. The diode output signal of only a few nanoseconds is very satisfactory for the new colliders.<<ETX>>