CP violation in B->Dh decays where D->Ksh'h'

Thesis

This thesis presents a measurement of the Cabibbo-Kobayashi-Maskawa angle gamma using B->DK and B->Dpi decays, where the D meson decays to one of the final states KsPiPi and KsKK. The measurement relies on the distribution of signal decays over the phase space of the D decay, analysed using a model-independent method based on strong-phase measurements by the CLEO and BESIII collaborations. The measurement is performed using proton-proton collision data collected by the LHCb experiment during the full Run 1 and 2 of the Large Hadron Collider, corresponding to a total integrated luminosity of 8.7 inverse femtobarn at centre-of-mass energies of 7, 8, and 13 TeV. The measurement determines that gamma equals 68.7 degrees (plus 5.2 degrees, minus 5.1degrees defined the 1sigma confidence band), with an alternative solution corresponding to gamma+180 degrees. This is the most precise stand-alone measurement of gamma to date, and achieves a precision that is comparable to all earlier measurements of gamma combined.

The thesis also presents a phenomenological study of the impact of neutral kaon CP violation and material interaction on gamma measurements with B+/- -> Dh decays where the D meson decays in the final states KsPiPi and KsKK. The existing literature at the outset of the thesis work had estimated the potential bias to be O(1 degree) in B->DK decays and to scale with 1/r_B. This suggests potentially large biases for a measurement with B->Dpi decays, since r_B(Dpi) is much smaller than r_B(DK). However, the thesis argues that the actual impact is an order of magnitude smaller, as long as the CP-violation observables are determined based on the phase-space distribution of signal decays. This is demonstrated in a number of numerical studies that take the geometries of the LHCb and Belle II detectors into account.

Authors: Bjoern, M

• Alternative title: A measurement of the CKM angle γ at LHCb and understanding the impact of neutral kaon CP violation
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: LHCb; B Physics; CP Violation; Flavour Physics; Particle Physics; CKM Triangle
• Subjects: Particle Physics