Search for Free Decay of Negative Pions in Water and Light Materials

TL;DR

This study searches for free decay of negative pions in water and light materials to detect potential anomalous neutrino contamination, but finds no evidence and sets upper limits on decay rates.

Contribution

It provides the first upper limits on free decay of pi- in water and light materials, informing neutrino contamination models.

Findings

No free decay component observed in water, Beryllium, and Aluminum.

Established upper limits on free decay rates for each material.

Results constrain models of anomalous neutrino contamination.

Abstract

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.