Observations of Cerenkov radiation produced in large cosmic ray showers at 1500m above sea-level

Abstract

An experiment designed to measure Cerenkov radiation from cosmic ray extensive air showers was deployed at Dugway, Utah from October 1977 to March 1980. This thesis is concerned with Cerenkov light measurements made at Dugway during the second season of observation from October 1978 to March 1979.An introduction to cosmic rays and extensive air showers is followed by a review of previous studies (both theoretical and experimental) of Cerenkov radiation from EAS. Particular attention is given to Cerenkov light parameters which relate to the depth of electron cascade maximum. A detailed account of the design and performance of the array of Cerenkov light detectors is then given, combined with an account of the first season of observation from October to December 1977.The calibration of the equipment during the second season of observation is discussed, indicating the sensitivity of the equipment to a light flux. This is followed by a description of the procedure employed to reduce the data from the experiment. A small sample of the recorded showers was selected to form the basis of a preliminary analysis presented in this thesis. Analysis of this sample of showers enabled the average characteristics of Cerenkov radiation from showers of energy 5x10(^16) - 5x10(^17)eV to be determined. The study of the average characteristics of Cerenkov radiation indicated that the lateral distribution of photon density, the peak height and FWHM of the Cerenkov pulses were sensitive to the zenith angle and energy of the showers. From the lateral distribution of photon density a primary energy estimator was established. Consistency was found between the preliminary results presented here and computer simulations. There were also favourable comparisons between the results of the Dugway experiment and similar measurements made at other establishments. A survey of vertically incident computer simulations of extensive air showers indicated that the basic assumptions behind the recently introduced elongation theorem may not be valid. Finally, a review of the future work of the Dugway experiment is presented.