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UBC Theses and Dissertations

Improvements to the Range Stack Straw Chambers for the measurement of K+-(pi)+vv Li, Xinghua

Abstract

Experiments E787/E949 at Brookhaven National Lab are aiming to measure the rare decay K⁻ —> π⁺ vv, expected in the Standard Model to have a branching ratio on the order of 10 ⁻¹⁰ . This thesis is related to improvements to the performance of one of the subsystems - the Range Stack Straw Chambers (RSSCs) which are designed to assist in the charged particle tracking and range measurements. There was a longstanding problem of poor resolution in the RSSCs longitudinal (z) measurement. In this thesis, we focus on understanding the sources of the problem and testing of a solution - a new electronics front end amplifier board developed by the TRIUMF electronics group. The new electronics uses two discriminator thresholds: the high threshold serves to remove cross talk effects and the low threshold serves to reduce time walk effects, resulting in improved resolution. Bench tests of the new system at TRIUMF from 1999 - 2001 showed significantly improved z resolution. A factor of 2 improvement was obtained, giving a z resolution of 1.5 cm. Initial results from E949 cosmic ray and muon data show a substantial z measurement improvement.

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