This thesis investigates the resonant structure of the Cabibbo-suppressed decay $D^0 \to \pi^+ \pi^- \pi^0$, the needed theoretical approach and the relevant experimental techniques to measure the time-integrated CP asymmetries using an amplitude analysis. The measurement uses a sample of $pp$ collisions recorded by the LHCb experiment during 2015-2018, corresponding to an integrated luminosity of 5.7 ${\rm fb}^{-1}$. The $D^0$ mesons are reconstructed from prompt $D^{*+}$ meson decaying into $D^0 \pi^+$, allowing the flavour at production to be assigned from the pion charge. The selected sample contains more than $2350 \times 10^{-3}$ signal events with a signal purity of about 90\%, allowing the most precise amplitude modelling of this $D^0$ decay to date. An amplitude analysis exploiting the rich intermediate resonant structure provided by the three-body phase space is performed. The magnitudes and phases for various decay channels are extracted from data using an unbinned maximum likelihood fit, from which their fractions can be inferred. The variations of the model acceptance across the phase space are also corrected from the theoretical formulation. The obtained amplitude model identifies a total of 10 intermediate resonant components and one non-resonant $\pi^+\pi^-$ S-wave component. The prominent contributions are found to be the $\rho(770)$ resonances, with fit fractions 74.28\% ($\rho^+(770)$), 26.88\% ($\rho^0(770)$), 40.25\% ($\rho^-(770)$).
- Amplitude analysis
- High-Energy physics experiment
- Charm physics
- CP violation
Amplitude analysis and search for CP violation with $D^0 \to \pi^+ \pi^- \pi^0 $ decay with Run-II data
Li, L. (Author). 1 Aug 2023
Student thesis: Master of Science by Research