The Standard Model of physics is likely the most self-consistent theory in modern science. The theory accounts for all the types of particles and interactions in nature and makes many detailed predictions concerning the yet unobserved phenomena. Pions and muons have historically provided essential information regarding electroweak interactions and in modern times are studied to a high precision as
pion decays are used as sensitive probles for physics Beyond the Standard Model (BSM). Comparisons of the π→μν(γ) and the chirally supressed π→eν(γ) presents the best test for electron-muon universality, an assumed feature of the Standard Model. Violations of universailty may indicate BSM features such as
leptoquarks, massive neutrinos, or several other new possibilities.
The PEN collaboration, led by a group from the University of Virginia, has undertaken to measure the pion electronic decay branching ratio (π→eν(γ)/Γ(π→μν(γ)) with a relative uncertainty of 5 X 10-4 or better. The experiment uses an active target and beam counters, a mini-time projection chamber for beam tracking
as well as multi-wire proportional chambers, plastic scintillating hodoscopes and a spherical pure CsI electromagnetic calorimeter. This talk will cover the analysis methods and backgrounds encountered in the PEN experiment as well as the various challenges and systematics that arises. A brief overview of an upcoming experiment will also be mentioned.
