Detector for measuring the π+ → e+νe branching fraction

A. A. Aguilar-Arevalo, M. Aoki, M. Blecher, D. Vom Bruch, D. Bryman, J. Comfort, S. Cuen-Rochin, L. Doria, P. Gumplinger, A. Hussein, Y. Igarashi, N. Ito, S. Ito, S. H. Kettell, L. Kurchaninov, L. Littenberg, C. Malbrunot, R. E. Mischke, A. Muroi, T. NumaoG. Sheffer, A. Sher, T. Sullivan, K. Tauchi, D. Vavilov, K. Yamada, M. Yoshida

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


The PIENU experiment at TRIUMF is aimed at a measurement of the branching ratio Re/μ = Γ((π+→e+νe)+(π+→e+νeγ))/Γ((π+→μ+νμ)+(π+→μ+νμγ)) with precision <0.1%. Incident pions, delivered at the rate of 60 kHz with momentum 75 MeV/c, were degraded and stopped in a plastic scintillator target. Pions and their decay product positrons were detected with plastic scintillators and tracked with multiwire proportional chambers and silicon strip detectors. The energies of the positrons were measured in a spectrometer consisting of a large NaI(Tl) crystal surrounded by an array of pure CsI crystals. This paper provides a description of the PIENU experimental apparatus and its performance in pursuit of Re.

Original languageEnglish (US)
Pages (from-to)38-46
Number of pages9
JournalNuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
StatePublished - Apr 25 2015


  • CsI
  • NaI(Tl)
  • Pion decay
  • Scintillation detectors

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Instrumentation


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