UNC-CH Physics and Astronomy Dissertation Defense

Chelsea Bartram

“CALIOPE, A Search for CPT-Violation in Positronium”

We present the results of a search for CPT-violation in ortho-positronium decay with CALIOPE, or CPT Aberrant Leptons in Ortho-Positronium Experiment. Positronium, a bound state of an electron and positron, occurs in both the singlet and triplet state. The triplet state, ortho-positronium (o-Ps), decays primarily into three gamma rays. CPT-violation could potentially manifest itself in angular correlations between the directions of the three photons and the spin of the o-Ps. The APEX annular array of NaI(Tl) detectors is located at Triangle Universities Nuclear Laboratory (TUNL) and has been dedicated solely to CALIOPE since August of 2018. We present the results of several months of continuous data-taking with 75% angular coverage, in addition to a comprehensive systematics study. We suggest improvements that would make our search competitive with the most sensitive CPT-violation searches in o-Ps performed to date.