The Lsnd Puzzle in the Light of Miniboone Results

Reconciling the LSND evidence1 for ν̄μ → ν̄e oscillations with the global neutrino data reporting evidence and bounds on oscillations remains a long-standing problem for neutrino phenomenology. Recently the MiniBooNE experiment 2,3 added more information to this question. This experiment searches for νμ → νe appearance with a very similar L/Eν range as LSND. No evidence for flavour transitions is found in the energy range where a signal from LSND oscillations is expected (E > 475 MeV), whereas an event excess is observed below 475 MeV at a significance of 3σ. Two-flavour oscillations cannot account for such an excess and currently the origin of this excess is under investigation 2, see also 4. MiniBooNE results are inconsistent with a two-neutrino oscillation interpretation of LSND at 98% CL3, see also 5. The exclusion contour from MiniBooNE is shown in Fig. 1 (left) in comparison to the LSND allowed region and the previous bound from the KARMEN experiment6, all in the framework of 2-flavour oscillations.