Testing Lepton Flavor Universality with Rare Pion Decays

The Standard Model (SM) of particle physics is the best available
theoretical framework to predict the subatomic interactions between
the fundamental elements of known matter. The PIENU experiment at
TRIUMF makes a precise measurement for one of the SM’s best
calculated predictions involving the force that governs radioactive
decays. If a measurement is consistent with the SM, better
constraints can be set on theories which extend the SM. In some
instances, these constraints can far exceed the reach of direct
searches at high energy colliding beam facilities like the Large
Hadron Collider at CERN. Most remarkably, a deviation from the SM
expectation could imply the presence of new physics effects not
included in the SM. This work describes the analysis of a dataset
including 3 million π+ → e + ν_e events. Major experimental
systematic problems have been solved, allowing for increased
precision by a factor of two over PIENU’s previous measurement from
2015.

Additionally, a new generation experiment of rare pion decay
measurement to reach SM calculation levels is under consideration
and the plan was presented at SNOWMASS 2020.

https://www.snowmass21.org/docs/files/summaries/RF/SNOWMASS21-RF2_RF3-048.pdf [www.snowmass21.org]

http://hdl.handle.net/2429/69938