A study of semileptonic and 2-body decays of charm strange baryons, a search for CP violation in Xi hyperon decays and a study of surface-treated planar microstrip gas chambers

Mary Bishai, Purdue University

Abstract

Using the CLEO II detector at the Cornell Electron Storage Ring we search for evidence of [special characters omitted] production at e+e − machines in the decay mode Ωc → Ω e+νe. We find 10.4 ± 3.8 candidate events. The probability that the background accounts for all events in the signal region as a statistical fluctuation is 7.7 × 10−4. Our result is B([special characters omitted] → Ω−e+ν e) · σ(e+ e− → [special characters omitted]X) = 0.22 ± 0.08pb. We have measured the product of the decay asymmetry parameters, αΛα Ξ, in the decay chain Ξ− → Λπ −, Λ → p+π −. We find αΛαΞ = −0.293 ± [special characters omitted] which is in good agreement with the current world average α ΛαΞ = −0.293 ± 0.007. Using our reconstructed sample of 4204 ± 75 Ξ− and similar number of Ξ+, we search for evidence of direct CP violation by measuring the asymmetry, [special characters omitted], in the angular distribution of Ξ → Λπ charge conjugate states. In the Standard Model, direct CP violation in hyperons is expected to occur at the 10−4–10−5 level. The observation of CP violation at a higher level may indicate the presence of new physics. We find no evidence of CP violation: [special characters omitted] ≃ AΞ + A Λ = −0.057 ± 0.064 ± 0.028. Given the world average AΛ = −0.03 ± 0.06, we find AΞ = −0.03 ± 0.06 ± 0.07. The systematic error is dominated by the AΛ measurement. We have measured the [special characters omitted] decay asymmetry parameter in the decay [special characters omitted] → Ξ−π+. We find [special characters omitted]αΞ = 0.26 ± [special characters omitted], using the world average of αΞ = −0.456 ± 0.014 we obtain [special characters omitted] = −0.56 ± [special characters omitted] where [special characters omitted] is <0.1 at the 90% CL. The central value occupies the middle of the theoretically expected range but is not yet precise enough to choose between models. We report on the study of surface treated planar microstrip gas chambers. We present the first observation of gas gain suppression in an ion-implanted kapton detector. We report on the results from a beam test on Kapton detectors carried out at the TRIUMF research facility in Vancouver, Canada. A study of the performance of microstrip gas chambers passivated by thin semiconducting glass and plastic films is presented.

Degree

Ph.D.

Advisors

Shipsey, Purdue University.

Subject Area

Particle physics

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