Search for CPT Violation with the FOCUS Experiment and Measurement of Λ_b lifetime in the decay Λ_b → J / Ψ Lambda with the D0 Experiment

Abstract

This dissertation describes two different projects from two different experiments. We have performed a search for CPT violation in neutral charm meson oscillations using data from the FOCUS Experiment. While flavor mixing in the charm sector is predicted to be small in the Standard Model, it is still possible to investigate CPT violation through a study of the proper time dependence of a CPT asymmetry in right-sign decay rates for D 0 → K − π + and D0 → K + π − . This asymmetry is related to the CPT violating complex parameter ξ and the mixing parameters x and y: A CP T ∝ Re ξ y − Im ξ x. We determine a 95% confidence level limit of −0.0068 < Re ξ y − Im ξ x < 0.0234. Within the framework of the Standard Model Extension incorporating general CPT violation, we also find 95% confidence level limits for the expressions involving coefficients of Lorentz violation of (−2.8 < N (x, y, δ)(∆a 0 + 0.6 ∆a Z ) < 4.8) × 10 −16 GeV, (−7.0 < N (x, y, δ)∆a X < 3.8) × 10 −16 GeV, and (−7.0 < N (x, y, δ)∆a Y < 3.8) × 10 −16 GeV, where N (x, y, δ) is a normalization factor that incorporates mixing parameters x, y and the doubly Cabibbo suppressed to Cabibbo favored relative strong phase δ.We also present measurements of the Λ 0 b lifetime in the exclusive decay channel Λ 0 b → J/ψΛ with J/ψ → µ + µ − and Λ → pπ − , the B 0 lifetime in the decay B 0 d → J/ψK 0 S with J/ψ → µ + µ − and K 0 S → π + π − , and the ratio of these lifetimes. The analysis is based on approximately 225 pb −1 of data recorded with the DØ detector in pp collisions at √ s = 1.96 TeV.The Λ 0 b lifetime is determined to be τ (Λ 0 b ) = 1.36 ± 0.30 (stat) ± 0.07(syst) ps, the B 0 lifetime τ (B d ) = 1.43 ± 0.12 (stat) ± 0.04 (syst) ps, and the ratio τ (Λ b ) τ (B d ) = 0.95 ± 0.22 ± 0.05. viiIn contrast with previous measurements using semileptonic decays, this is the first determination of the Λ 0 b lifetime based on a fully reconstructed decay channel.viii