Search for Free Decay of Negative Pions in Water and Light Materials
  We report on a search for the free decay component of pi- stopped in water and light materials. A non-zero value of this would be an indication of anomalous nu_e contamination to the nu_e and nu_mu_bar production at stopped-pion neutrino facilities. No free decay component of pi- was observed in water, Beryllium, and Aluminum, for which upper limits were established at 8.2E-4, 3.2E-3, and 7.7E-3, respectively. 
T. Numao, Yu.I. Davydov, J-M. Poutissou, T.C. Awes, V. Cianciolo, S.   Berridge, W. Bugg, Yu. Efremenko, R. Gearhart and S. ...