Search for massive neutrinos in π→eν decay

We describe the details of an experiment designed to search for the admixture of massive neutrinos into electron-flavor neutrinos by observation with high resolution of the positron momentum spectrum in pi --> e + nu decay. No indication was found for such an admixture and the corresponding mixing amplitude was constrained below the U(ei)2 less-than-or-equal-to 10(-6) region for neutrinos of approximately 30 MeV/c2 mass.