Single and Double Direct Photon Production in Pion-Proton Interactions at 280 GeV/c

[摘要] This thesis presents results on single and double direct photon production in pi-p interactions at an incident beam momentum of 280 GeV/c, using data recorded by the CERN experiment WA70 at the Omega Prime Spectrometer in October and November 1986. The single direct photon cross-section is measured over the transverse momentum (pt) range 4.5+7.0 GeV/c and the Feynman x range -0.45→+0.45. The ratio of single direct photon to pi production was measured over the same pt range. The double direct photon cross-section is measured over the pt range 3.0→6.0 GeV/c. Chapter One contains a short overview of Quantum Chromodynamics (QCD) and a discussion of the theoretical framework used to describe single and double direct photon production. A brief review of recent experimental results concludes the chapter. Chapter Two describes the experimental apparatus used by WA70, in particular the large fine-grained calorimeter which was built specifically for the experiment. Chapter Three discusses the computer programs used in the processing and analysis of the data. The reconstruction programs GLOBAL, OMGEANT and TRIDENT are described, as are the LUND and TWISTER Monte Carlo programs. Chapter Four consists of a detailed discussion of the cuts made to isolate the single direct photon and pi signals, with special note being made of the problem of muon 'halo' contamination. Chapter Five describes the determination of the detection efficiencies and acceptances for the single direct photon and pi signals and the calculation of the background to the single direct photon signal. In Chapter Six the single direct photon and pi cross-sections are presented. A parametrisation of both is made, and the current results compared with those from the 1984 and 1985 experimental runs. The direct photon cross-section is compared with results published by the contemporary direct photon experiments NA24 and UA6. This cross-section is then compared with the predictions from recent Beyond-Leading-Log (BLL) QCD calculations. A discussion of how the data can be used to measure the gluon distribution function and the fundamental QCD parameter AQCD is also given. Chapter Seven is devoted to the topic of double direct photons. The cuts used to isolate this signal are listed, followed by a detailed description of the background calculation. The detection efficiency and acceptance are discussed, and the final double direct photon cross-section presented. A description of the measurement of the coupling strength of the strong force aS using the double and single direct photon cross-sections is given. The chapter concludes with a discussion of how the choice of scaling affects the interpretation of these measurements. Conclusions are presented in the short Chapter Eight.

[发布机构] University:University of Glasgow

[关键词] High energy physics