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A helium high temperature drift chamber

University of British Columbia

We have built and operated a high temperature TPC which was integral to a polarized target originally designed for a triton detector at TRIUMF. The TPC is the key part for the improvement of the measurement accuracy in the study of the spin dependence of the reaction: μ⁻ + ³He → ³H + vμ. This spin dependence is very sensitive to the induced pseudoscalar form factor, Fp, which is very important for our understanding of strong interactions at low energies, but about which relatively little is known experimentally. The nuclear capture rate in ³He is proportional to (1 + AvPv cos θ), where Pv is the muon polarization and θ is the angle between the muon polarization and the direction of the recoil triton. The last E683 data run at TRIUMF gives Av = 0.59 ± 0.09 ± 0.10 using a Princeton ionization chamber as the triton detector. The design, construction and development of the TPC is the main emphasis of this thesis. An extensive study of the TPC performance as a function of the electric field at various temperatures and different helium-nitrogen mixtures has been made. The properties of electron transport and gas amplification in mixtures of helium with a variety of molecular additives have been studied and compared with a standard argon based gas mixture. The optimized operating condition using helium/nitrogen(97:3) mixture achieves an angular resolution of about ±1 degree. The directional information can be obtained by fitting the anode pulse shapes based on a detailed model of the detector. Future improvements of the detector will make the TPC a candidate for a new generation of this experiment, which should then provide a more precise measurement of Av and hence, a more precise form factor, Fp. Thus, it will provide a better test of our understanding of QCD at low energy.

Thesis/Dissertation

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2009-06-30

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http://hdl.handle.net/2429/9884

Physics

University of British Columbia

UBCV

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