A.W. Halley

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.

Performance of a cluster of multi-anode photomultipliers equipped with lenses for use in a prototype RICH detector

A cluster of multi-anode photomultiplier tubes (MaPMTs) equipped with focusing lenses in front of the tubes was tested in a prototype ring imaging Cherenkov (RICH) detector in a charged particle beam. The readout electronics were capable of capturing the data at 40 MHz. The effects due to charged particles and magnetic field on the MaPMT performance were also studied. The results are used to evaluate the MaPMT as a possible photodetector for the LHCb RICH detectors.

THE NEW ALEPH SILICON VERTEX DETECTOR

The ALEPH collaboration, in view of the importance of effective vertex detection for the Higgs boson search at LEP 2, decided to upgrade the previous vertex detector. Main changes were an increased length (+/- 20 cm), a higher granularity for r phi view (50 mu m), a new preamplifier (MX7 rad hard chip), a polymide (upilex) fan-out on z side to carry the signals from the strips to the front-end electronics outside the fiducial region reducing consequently the passive material in the central region by a factor of two. The detector, the running experience and its performance will be described

First observation of Cherenkov ring images using hybrid photon detectors

Abstract A ring-imaging Cherenkov detector, equipped with hybrid photon detectors, has been operated in a charged-particle beam. Focussed ring images from various particle types were detected using silica aerogel, air and C 4 F 10 gas radiators. The detector, a prototype for the CERN LHC-B experiment, is described and first observations are reported.

Latest beam test results from RICH prototypes using hybrid photo detectors and multi anode PMTs

Abstract Beam tests were performed in 1998 to investigate the performance of a prototype of the downstream RICH of the LHCb using hybrid photo-diodes and multi anode PMTs. The angular resolutions obtained from these photodetectors under various experimental configurations are compared with the expectations from simulation.

The spatial resolution of the ALEPH TPC

The present understanding of the factors which limit the rφ measurement accuracy of the ALEPH time projection chamber is outlined. The resolution for high-momentum tracks is shown to be dominated by the E × B and angular affects.

Construction and performance of the new ALEPH Vertex Detector

A new Silicon Vertex Detector was developed for the ALEPH experiment and first installed for the high energy run at 130 GeV at the end of 1995. The detector has an active length of 40 cm and consists of two concentric layers of silicon wafers with double-sided readout. It extends the angular coverage, has only half the passive material as the former detector in the tracking volume and is radiation hard to cope with the higher level of radiation background expected for the LEP2 phase. The construction and the performance of the detector is described.

Irradiation tests of double-sided silicon strip detectors with a special guard ring structure

The results of the first irradiation tests of newly designed silicon microstrip detectors performed with 21 MeV protons at the Max-Planck-Institut in Heidelberg are presented. The detectors were developed and produced by the semiconductor laboratory of the Max-Planck-Institut in Munich. Novel guard ring structures allow operation of the detectors at voltages exceeding 300 V.

The FASTBUS readout system for the Aleph time projection chamber

The readout system for the Aleph central tracking detector, a large time projection chamber (TPC), consists of more than 100 FASTBUS crates with approximately 1000 FASTBUS modules. The detector and its associated electronics are briefly presented, followed by a more detailed description of the readout and control system. The discussion covers the sector readout, electronics calibration, front-end data acquisition, data pipelining, and service request handling. Experiences with the system are discussed. >

Monitoring the Stability of the ALEPH Vertex Detector

Abstract The ALEPH Silicon Vertex Detector features an optical fibre laser system to monitor its mechanical stability. The operating principle and the general performance of the laser system are described. The experience obtained during 1997 and 1998 operations confirms the important role that such a system can have with respect to the detector alignment requirements. In particular, the laser system has been used to monitor short-term temperature-related effects and long-term movements. These results and a description of the laser-based alignment correction applied to the 1998 data are presented.