Search for CP Violation in charm meson decays to final states with at least one neutral particle

Abstract

CP violation is a phenomenon embedded within the Standard Model to explain the matter anti-matter asymmetry seen in the universe today. Searches for CP violation in hadrons containing charm quarks are interesting in the field of flavour physics because they contain up-type quarks which could be sensitive to new interactions/particles that would leave down-type quarks unaffected. Beyond Standard Model (BSM) physics can enhance the magnitude of CP violation in decays of hadrons containing charm quarks, hence measurements of CP asymmetry in charm decays provide an excellent laboratory to probe the precision of the standard model. The decay of neutral charm mesons into a final state containing at least one neutral particle are sensitive to beyond standard model physics. One family of decays known as radiative charm decays of the form D0 → V γ (V = φ, ρ, K∗) can have CP asymmetries reaching O(10^−3) in the standard model and can be enhanced by an order of magnitude by new particles entering quantum loop transitions which are an inherent feature of radiative decays. Measurement of CP asymmetries and branching fractions of radiative charm decays has never been performed at a hadron collider due to busy collision environment. In this thesis, a method to measure the CP asymmetries and branching fractions of the family of radiative decays is presented as well as a proof of principle on how to extract the signal yield in the D0 → φγ channel by performing multidimensional fits to data recorded in the first operational run of the LHC. Including data from the second operational run would allow LHCb to make the most precise measurement of the CP asymmetries and branching fractions for radiative decays, an unprecedented feat for a hadron collider. This thesis also analyses D0 → π−π+π0 decays which have non-trivial phase space due to contributions from various resonances that contribute to strong phase varying across the Dalitz space. This can provide additional sensitivity to CP violation. The search for CP violation is performed using a statistical method known as the energy test which computes a T value that is converted into a p-value to quantify whether the data is consistent with the null hypothesis of CP symmetry. A p-value of 0.62 was obtained once the energy test was applied to the D0 → π−π+π0 channel which is consistent with the null hypothesis of CP symmetry.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Christopher Parkes (Supervisor) & Marco Gersabeck (Supervisor)