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Precision measurements of rare pion decays in the Pioneer experiment

Speaker(s) / Presenter(s):
Tim Gorringe (University of Kentucky)

Precision measurements of rare decays of charged pions offer important tests of the standard model. The ratio of pi+ -> e+ nu to mu+ nu decay provides the best test of electron–muon weak universality and is uniquely sensitive to non-V-A exotic currents. The rate of pion beta decay pi+ -> pi0 e nu offers a theoretically pristine sensitivity to the Vud matrix element of the CKM matrix.

In this talk I'll discuss the plans by the Pioneer collaboration for a twenty-fold improvement in the determinations for the rare pi+ -> e+ nu and pi+ -> pi0 e nu decays. These determinations involve measurements of relative yields from stopped pions of 70 MeV monoenergetic electrons from pi+ -> e+ nu decay, coincident photons from pi0's produced in pi+ -> pi0 e nu decay, and the 0-53 MeV Michel electrons from mu decay.  
The measurements demand both high statistics and careful understanding of systematic effects. To reach these goals we plan to utilize emergent technologies for both electromagnetic calorimetry and 4-dimensional, high-granularity tracking of pions, muons and electrons.
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