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UBC Theses and Dissertations

A Monte Carlo study of Pion Beta Decay in the RMC spectrometer Veillette, Sacha


Through Monte Carlo simulation, this thesis assesses the efficiency, strengths and weaknesses of the TRIUMF Radiative Muon Capture pair-spectrometer for the purpose of performing a measurement of Pion Beta Decay. We discuss the importance of Pion Beta Decay in terms of current theories of particle physics, with a special emphasis on the Standard Model. Properties of this weak process are described and some past and ongoing experimental efforts are briefly reviewed. The actual Radiative Muon Capture facility is described since on its configuration, the signatures of the relevant processes, the Pion Beta Decay signal and the experimental backgrounds. The detailed manner by which the respective rates have to be evaluated is also explained. We concentrate on the work done to obtain a realistic simulation for processes with branching ratios of the order 10- 8 or less. The basic Monte Carlo software used, CERN's GEANT 3 program, is introduced before the major modifications made to the package are described in detail. The optimal analysis scheme for the present detector is assessed by studying a variety of energy and geometry cuts on the Monte Carlo data. The expected experimental rates are obtained from a complete analysis by combining various cuts. We discuss the results in terms of the present experimental setup. Some possible modifications to the RMC pair-spectrometer are discussed based on the simulated properties of Pion Beta Decay. Other possible modifications as well as alternative detector designs are also discussed briefly. This study shows that, due to an overall low acceptance for two-photon events, the present detector is not suitable for a Pion Beta Decay measurement. However, because of its unique features for the reconstruction of photons from e+e- conversion pairs, the spectrometer does present great advantages for background reduction for a Pion Beta Decay signal if a factor of 10 increase in the pion flux (π+) could be obtained.

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