CP violation at LHCb and a novel measurement of hadronic charm inputs at BESIII

Thesis

The angle γ of the Unitarity Triangle is measured by studying CP violation in B0 → DK∗(892)0 decays, where D denotes a superposition of the D0 and D0 mesons. The value γ = (49+22−19)◦ is determined, where the uncertainty combines the statistical and systematic sources. The measurement is made using a dataset with an integrated luminosity of 9fb-1, and is collected by the LHCb experiment in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The procedure examines CP violation across the kinematic phase space of the D to K0Sπ+π- and D to K0SK+K- decays. The angle γ is interpreted from the data using hadronic inputs describing the D decays. The values of these inputs are provided by the BESIII experiment using quantum-correlated DD meson pairs, rather than relying on those provided by an amplitude model.

The second half of this thesis presents the determination of a hadronic charm parameter, specifically the strong-phase difference between D0 and D0 decays to the K-π+ final state, δKDπ. A dataset, which is collected by the BESIII experiment in e+e- collisions at centre-of-mass energies between 4.13 and 4.23 GeV, and has an integrated luminosity of 7.13fb-1, is used for the analysis. The parameter δKDπ is measured by exploiting interference in DD to K-π+ vs. X decays, where X is a CP eigenstate or K0Sπ+π-. It is determined to be δKDπ = (192.8+11.0+1.9-12.4-2.4)◦, where the first uncertainty is statistical and the second is systematic. The study presented is the first to observe and use the quantum correlations in DD pairs produced above the ψ(3770) resonance. At these higher energies, the DD pairs are produced in even and odd eigenstates of the charge-conjugation operator, C, compared to only the latter at ψ(3770). Simultaneously using the C-even and C-odd DD pairs allows access to novel experimental observables that significantly reduce systematic uncertainties.

Authors: MacKay, I

• DOI: 10.5287/ora-b7amqea9x
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: LHCb; BESIII; CP violation; strong phase
• Subjects: CP violation (Nuclear physics)