Howarth, Christopher; (1990) Studies of small-angle electron positron collisions at high energy. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is based on work performed on the forward detectors for the JADE experiment at DESY, Hamburg, and the OPAL detector at CERN, Geneva. The forward detectors are both used to monitor the luminosity of the colliders, by measuring the rate of small angle Bhabha scattering, and to tag single electrons in photon-photon scattering events. The JADE forward detector is an electromagnetic calorimeter of the lead/scintillator sandwich type. An energy calibration of this calorimeter was made, using data taken towards the end of PETRA running, increasing its resolution by almost a factor of two. The performance of the detector was modelled using a Monte Carlo program which reproduced the major features of the real data; in particular the behaviour of the ratios of pulse heights in adjacent blocks of the calorimeter. These ratios could then be calibrated to give radial and azimuthal positions of showers as well as to determine the detector acceptance. This permitted a calculation of the luminosity to be made, for comparison with that calculated from looking at Bhabha events in the lead glass barrel. The acceptance measurement has also been adopted for use in two photon physics studies (see paper [30]). A study of the systematic errors incurred in making a luminosity measurement using the fine luminosity counters and calorimeter of the OPAL forward detector were studied including beam parameter fluctuations, counter position uncertainties, beampipe interactions and accidental coincidences.

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