Neutrino oscillations at accelerators: LSND, KARMEN and MiniBooNE

Abstract

The current status of accelerator based ν-oscillation searches in the appearance channel ν μ → ν e is reviewed. While two experiments (LSND and KARMEN) at the beam stops of 800 MeV proton accelerators have finished data taking, a third experiment (MiniBooNE) at the Fermilab Booster will soon start measurements. All three experiments are short baseline oscillation experiments performed at L/E ≈ 1, corresponding to a sensitivity to the Δ m 2-scale above 0.1 eV 2. The LSND experiment at LANSCE in Los Alamos has taken data from 1993–98 and observed an excess of ν e events interpreted as evidence for ν μ → ν e appearance. Final results from the entire LSND data sample suggest oscillations parameters in the range Δ m 2 = 0.2–10 eV 2, implying that at least one neutrino could have a mass greater than 0.4 eV. The neutrino experiment KARMEN at the spallation source ISIS in England has searched for ν μ → ν e oscillations from 1997–2001, following an extensive upgrade which eliminated cosmic ray induced background reactions. Analysis of three years of data from 1997–2000 shows no oscillation signal. The corresponding KARMEN2 oscillation limit excludes a large part of the LSND parameter space while leaving some statistical space for oscillations at small values of Δ m 2. The MiniBooNE experiment has the sensitivity to search for ν μ → ν e oscillations in the same parameter range as LSND and KARMEN with entirely different systematics. MiniBooNE is expected to improve the final KARMEN2 sensitivity by another factor of 2 so that its results should clarify the contradictory results of KARMEN and LSND.