Glimpsing one of Nature’s Secrets: The po Lifetime

Dr. Dustin E. McNulty
Department of Physics
University of Massachusetts


The p-mesons are nature’s lightest and simplest hadronic systems.  As such, they are readily produced in the laboratory and lend themselves as a test-bed for checking the predictions of fundamental theories of the standard model; one such prediction concerns the lifetime of the po with a mean lifetime of approximately 10-16 seconds, the po decays electromagnetically into 2 photons 99% of the time, and it turns out that this decay is dominated by a quantum anomaly. In other words, the relatively quick decay proceeds only because a symmetry of the classical theory is anomalously broken or violated in the quantized version. A measure of the po togg  decay rate or partial decay width, Ggg , represents a direct probe of the anomaly and a test of the underlying theory. The PrimEx Collaboration at Jefferson Lab has extracted Ggg from precision measurements of  po photo-production cross sections. Measurements were made using 5% radiation length nuclear targets of 12C and 208Pb with incident photons between 4.9 and 5.5GeV tagged by the Hall B tagger facility. The po decay photons were detected by a specially constructed high resolution hybrid calorimeter. In this presentation, recent results from the PrimEx measurements will be given along with a general introduction and overview of the physics, experimental design and setup, detector performances, and data analysis strategies and techniques.