School of Science Department of Physics 58 Investigation of CP Symmetry in Neutrino Oscillation Supervisor: LUK Kam Biu / PHYS Student: LAI Chun Kit / PHYS Course: UROP 1100, Fall Neutrino oscillation is a phenomenon describing the inter-conversion between neutrino flavors. As neutrinos are typically known for only participating in weak interactions which violates CP-symmetry, whether this phenomenon also breaks the symmetry is also of interest. This project attempts to find how well the CPviolating phase can be determined through simulation of muon neutrino converting into electron neutrino, finding its probability which has dependence on such phase. This is a progress report reflecting what I have learnt about the fundamentals of neutrino interaction and the cross-section for different types of scattering. Search for Light Dark Matter with Positronium Supervisor: LUK Kam Biu / PHYS Student: LAM Chi-yin Sienna / PHYS-IRE Course: UROP 3200, Fall This project aims to examine positronium decay, using quantum dot-doped scintillators and photomultipliers to observe the decay branching ratios. Positronium decay is theoretically understood and experimentally verified, so any anomalies in the decay pathways could indicate the presence of dark matter candidates. There are 2 forms of the positronium, orthopositronium and parapositronium. Orthopositronium is the preferred form because it produces 3 photons, which are easier to triangulate. The ratios of the positronium forms are determined by the medium. Ideally, the medium would also be a scintillator because it could immediately detect when a positron enters it, making it far simpler to determine when positronium is formed. Search for Light Dark Matter with Positronium Supervisor: LUK Kam Biu / PHYS Student: YU Ho Hin / PHYS-IRE Course: UROP 1100, Spring Studies have shown that some energy has disappeared when a positronium decays, hinting the existence of invisible light dark matter. An experiment is designed and to be constructed to search for the light dark matter. A sodium-22 source emits a positron during decay, which enters silica aerogel and linear alkyl benzene to form positronium. The positronium decays into gamma rays, which are detected by hodoscopes or cesium iodide photocathodes. Four designs of a detector using hodoscopes are proposed, approximating a spherical shell, approximating a spherical shell with hodoscope rotations, a polygon cylinder, and a polygon cylinder with shifting. The experiment is still in progress, with the data analysis to be initiated once the experiment design is completed and constructed.
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