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UBC Theses and Dissertations

The Chaos second level trigger McFarland, Sheila Joy


In the summer of 1993, a group at TRIUMF commissioned the Canadian High Acceptance Orbit Spectrometer (CHAOS). This is a 360° spectrometer that was built to study Π[sup ±]p elastic scattering and the (Π, 2 Π) reaction in order to investigate the possible effects of chiral symmetry in QCD. An important part of the vast readout electronics is the second level trigger, which performs several fast calculations in hardware to determine the merit of an event before writing it to tape. The trigger performs various cuts on single outgoing tracks: momentum, polarity, distance of closest approach to the origin of CHAOS, and momentum versus scattering angle. In addition, the trigger can look for two such acceptable tracks and then perform cuts based on the sum of the momenta and the comparison of the polarities; this section in particular is crucial for the success of the (Π, 2 Π) program. Finally, the second level trigger can survey the incoming beam and reject events in which an incident pion decayed to a muon before reaching the CHAOS target. This thesis will first provide an introduction to the theoretical motivation behind CHAOS and also outline the various components of the spectrometer in brief. The remainder of the thesis will discuss in detail the purpose and operation of the different sections of the second level trigger.

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