Charmingly Radiative CP Violation

Fundamental symmetries have proven to be essential in our evolving understanding of elementary particle interactions. Two of the most common examples are the discrete parity (P) and charge conjugation (C) symmetries. While P represents a system that remains unchanged under space reflection, C describes a property between particles and their anti-particles. Both C and P are preserved by strong and electromagnetic processes but violated in weak decays. The violation of the combined charge-parity (CP) symmetry is one of the requirements of the generation of baryon asymmetry in the Universe. CP violation was first observed in 1964 in decays of particles containing one strange quark. Further measurements allowed to establish CP violation also in the bottom quark meson system, leading to the Nobel prize win for Kobayashi and Maskawa in 2008. Despite its many successes, the amount of CP violation predicted by their theory is orders of magnitude smaller than what is required to explain the observed matter-antimatter asymmetry in the Universe. It is therefore crucial to continue experimental investigations to search for possible new sources of CP violation. In decays of particles containing charm quarks, CP violation is expected to be small and challenging to observe experimentally. So far CP violation in charm has only been observed by the LHCb experiment in 2019. Decays in which one photon is radiated off the charm particle are of particular interest. CP violation effects in these radiative decays can be enhanced by non-standard dynamics. The latter can also affect the polarization of the photon and alter the lifetime of the charm particle. These decays therefore offer several ways to search for new physics. The latest generation of heavy-flavor experiments is hosted at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan. The asymmetric energy collider SuperKEKB accelerates electrons and positrons on a total circumference of 3km at respective beam energies of 7 and 4GeV. Located at the interaction point of both beams, the Belle II experiment is perfectly suited to study charm decays. The determination of flavor, i.e. the quark content of the charm particle at the time of production is crucial for these measurements. A new approach will be used which infers the charm flavor from all the other particles produced in a collision. This algorithm will be further improved with advanced machine learning techniques and by exploiting all the production mechanisms for charm particles. The newly-developed detectors of the Belle II experiment are able to measure lifetimes of charm particles with sub-percent precision. This will allow for a deeper insight into the understanding of radiative charm decays.