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Type: Thesis
Title: Direct CP Violation in B Meson Decays
Author: Hockley, Liam Christopher
Issue Date: 2020
School/Discipline: School of Physical Sciences
Abstract: The matter-antimatter asymmetry observed in nature is one of the largest open questions in particle physics and CP violation is a key requirement for such an asymmetry to exist. Although measurements of CP violation are typically too small to account for this asymmetry, in 2017 the Belle Collaboration reported a significant CP violation of ACP = -0.:90 ± 0.17 ± 0.03 in the 0.8 ≤ mKK ≤ 1.:1 GeV=c2 region of the K+K¯π± invariant mass in B± -> K+K¯ decays. Direct CP violation in B meson decays arises through the interference of tree and penguin amplitudes and can only occur if there are both strong and weak phase differences between the diagrams. We present several models for tree and penguin diagrams which proceed through a two stage decay process. These involve the f0(980) and φ(1020) resonances, both with masses around 1 GeV=c2, and we also test models involving non-resonant tree decay. Using these models, we calculate the CP asymmetry ACP in an attempt to justify the Belle results. We use an effective Hamiltonian based on the four-fermion interaction and the Operator Product Expansion to calculate the tree and penguin amplitudes, with Naive Factorisation applied to the hadronic matrix elements. We take several form factor descriptions of the factorised matrix elements, namely monopole and dipole dominance models. We find evidence that there may be a significant asymmetry present in the case of f0(980) tree interference with φ(1020) penguin intermediate states, although other models involving non-resonant tree decays perform better when taking into account the finite resolution of detectors. We present the following estimates of the CP asymmetry; ACP = -0:0007 to -0:0554 for the case of a tree diagram involving the f0(980) and a penguin involving the φ(1020); ACP = -0:0819 to -0:346 for the case of a non-resonant tree diagram and a penguin involving the f0(980); ACP = -0:0196 to -0:101 for the case of a tree amplitude receiving both non-resonant and f0(980) contributions, and a penguin involving the f0(980). Future work could look to use QCD factorisation or Lattice QCD to compute the hadronic matrix elements. If narrower constraints are placed on the properties of the f0(980) and the CKM matrix parameters, a more definitive conclusion may be reached on the influence of the f0(980) on the Belle result.
Advisor: Thomas, Anthony
Young, Ross
Dissertation Note: Thesis (MPhil) -- University of Adelaide, School of Physical Sciences, 2020
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