The Search for Neutrino Oscillations numubar->nuebar with KARMEN

TL;DR

The KARMEN experiment searched for muon antineutrino to electron antineutrino oscillations at 17.7m, setting new limits that challenge previous LSND evidence, with no oscillation events observed.

Contribution

This study provides the first stringent upper limit on muon to electron antineutrino oscillations at short baseline, constraining the parameter space suggested by LSND.

Findings

No oscillation events observed in data from 1997-1998.

Set an upper limit on mixing angle: sin^2(2θ) < 1.3×10^{-3} at 90% CL.

Excluded most of the parameter space favored by LSND evidence.

Abstract

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS. It provides numu's, nue's and numubar's in equal intensities from the pi+ mu+ decay at rest (DAR). The oscillation channel numub->nueb is investigated in the appearance mode with a 56t liquid scintillation calorimeter at a mean distance of 17.7m from the nu source looking for p(nue,e+)n reactions. The cosmic induced background for this oscillation search could be reduced by a factor of 40 due to an additional veto counter installed in 1996. In the data collected through 1997 and 1998 no potential oscillation event was observed. Using a unified approach to small signals this leads to an upper limit for the mixing angle of sin**2(2t) < 1.3x10^{-3} (90%CL) at large Dm**2. The excluded area in (sin**2(2t),Dm**2) covers almost entirely the favored region defined by the LSND numub->nueb evidence.