Search for Massive Neutrinos in the Decay pi --> e nu

TL;DR

This paper reports a search for massive neutrinos in pion decay, setting upper limits on neutrino mixing matrix elements in the 60-129 MeV/c^2 mass range, with implications for neutrino physics.

Contribution

The study provides new upper limits on neutrino mixing matrix elements in a previously unexplored mass range, improving constraints on neutrino properties.

Findings

Upper limits on |U_ei|^2 at 10^-8 level

Mass range 60-129 MeV/c^2 constrained

Suppressed background from decay chain

Abstract

Evidence of massive neutrinos in the pi --> e nu decay spectrum was sought with the background pi --> mu --> e decay chain highly suppressed. Upper limits (90% C.L.) on the neutrino mixing matrix element |U_ei|^2 in the neutrino mass region 60--129 MeV/c^2 were set at the level of 10^-8.