Model-independent measurement of the CKM angle γ in B±→ [h+h−π+π−]Dh′± (h = K, π) decays at LHCb and BESIII

Thesis

This thesis describes two complementary analyses related to the four-body D0 → K+K−π+π − and D0 → π+π−π+π − decays, where the ultimate objective is to study CP violation and measure the CKM angle γ. First, a model-independent determination of parameters describing the strong-phase difference between the D0 and D0 → K+K−π+π − decays is performed. The analysis uses a sample of quantum-correlated DD pairs produced in e+e − collisions at the ψ(3770) resonance. The data sample corresponds to an integrated luminosity of 16 fb−1, recorded by the BESIII detector. The measurement is performed in bins of phase space, using a five-dimensional binning scheme optimised for sensitivity to γ.

In the second part, a sample of pp collisions collected by the LHCb detector, corresponding to 9 fb−1 of integrated luminosity, is used to obtain a model-independent measurement of γ with the B± → Dh± decay, where h = K or π. The neutral charm meson subsequently decays to the four-body D → K+K−π+π − or π+π−π+π − modes. This is the first binned measurement of γ using these multi-body decays, utilising strong-phase parameters from BESIII as external inputs. Additionally, a study of the phase-space integrated CP-violating effects is also performed.

The result is γ = (53.6+8.6−6.7)◦, which is a combination of both phase-space binned and phase-space integrated CP-violating observables. It is one of the most precise stand-alone measurements of the CKM angle γ. The uncertainties are currently statistically dominated.

Authors: Tat, MD

• DOI: 10.5287/ora-gjveje5e9
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: B physics; BESIII; CKM; gamma; charm physics; CP violation; LHCb
• Subjects: Physics