KARMEN Limits on nu_e -> nu_tau Oscillations in 2-neutrino and 3-neutrino Mixing Schemes

TL;DR

The KARMEN experiment searched for nu_e to nu_tau oscillations using a high-resolution detector and found no evidence, setting limits on oscillation parameters in both two- and three-neutrino mixing schemes.

Contribution

This study provides the first comprehensive analysis of nu_e to nu_tau oscillations with five years of data, including a complete three-flavor mixing analysis and new limits on oscillation parameters.

Findings

No evidence for nu_e->nu_tau oscillations was observed.

Set 90% CL limits on sin^2(2θ) for various dm^2 ranges.

Performed a complete three-flavor neutrino mixing analysis.

Abstract

The 56 tonne high resolution liquid scintillation calorimeter KARMEN at the beam stop neutrino source ISIS has been used to search for neutrino oscillations in the disappearance channel nu_e->x. The nu_e emitted in mu+ decay at rest are detected with spectroscopic quality via the exclusive charged current reaction 12-C(nu_e,e-)12-N_g.s. almost free of background. Analysis of the spectral shape of e- from the nu_e induced reaction as well as a measurement of the absolute nu_e flux allow to investigate oscillations of the type nu_e->nu_tau and nu_e->nu_mu . The flux independent ratio R(CC/NC) of charged current events 12-C(nu_e,e-)12-N_g.s. to neutral current events 12-C(nu,nu')12-C* provides additional information in the oscillation channel nu_e->x . All three analysis methods show no evidence for oscillations. For the nu_e->nu_tau channel 90%CL limits of sin^2(2t)<0.338 for dm^2>100eV^2 and dm^2<0.77eV^2 for maximal mixing in a simple 2 flavor oscillation formalism are derived. A complete 3 flavor analysis of the experimental data from five years of measurement with respect to nu_e<->nu_tau and nu_e<->nu_mu mixing is presented.