Controlling penguin contributions to CP violation in B⁰→J/ψX decays

Abstract

Modern particle physics experiments are constantly searching for signs pointing to New Physics (NP) beyond the Standard Model (SM). One possible source for finding NP effects is Charge-Parity (CP) violation in particle-anti-particle mixing of neutral B_d(s) mesons. The strength of this CP violation can be parameterised by a weak mixing phase φ_d(s). Accurately measuring the weak mixing phase φ_d(s) and comparing it to SM predictions can provide a signal for NP. Because these mixing phases cannot be directly calculated from Quantum Chromodynamics (QCD), they require experimental input in order to make predictions. It has been known for some time that the results for the mixing phases based on experiments are contaminated by contributions from higher order Feynman diagrams known as penguin diagrams. Controlling these penguin contributions will be necessary in order to improve the precision of these mixing phases in the future. In this thesis the formalism for controlling these penguin contributions is explored. Using the GammaCombo software package a fit is made to the parameters describing these contributions as well as the weak mixing phase φ_d(s). Experimental input in the form of CP asymmetries in B⁰s→J/ψK0S, B⁰d→J/ψK⁰S, B⁰d→J/ψπ⁰, B⁰s→J/ψφ and B⁰d→J/ψρ⁰ decays is used for making a global fit to all parameters. This global fit allows for a direct extraction of the mixing phase φ_d(s) from the experimental input and does not require input from QCD calculations. The values for the mixing phases found using this approach agree with currently available measurements. Finally, the signal for NP is explored, also looking at how it might change with more accurate experimental input in the future.