The search for neutrino oscillations with KARMEN

Abstract

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS. It provides νµ's, νe's andνµ's in equal intensities from the π + -µ + -decay at rest (DAR). The oscillation channelνµ→νe is investigated in the appearance mode with a 56 t liquid scintillation calorimeter at a mean distance of 17.7 m from the ν-source looking for p (νe , 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 (2Θ) < 1.3 · 10 −3 (90% CL) at large ∆m 2 . The excluded area in (sin 2 (2Θ),∆m 2 ) covers almost entirely the favored region defined by the LSNDνµ→νe evidence.

Phenomenology of neutrino oscillations

“…The region of neutrino mixing parameters indicated by the results of the LSND experiments is presently explored also by the KARMEN experiment [375,[377][378][379][380][381][382]. The KARMEN experiment is located at the ISIS spallation neutron facility of the Rutherford Laboratories (UK).…”

“…In 1996 the experiment was upgraded to KARMEN 2, eliminating the main cosmic ray induced background component in the search forν µ →ν e oscillations [379]. So far, the KARMEN 2 experiment measured no events [375,[380][381][382], also no background events, of which 2.88 ± 0.13 events were expected. The resulting exclusion curve obtained with a Bayesian analysis [375] is shown in Fig.…”

Resolving the solar neutrino problem with KamLAND

“…All experiments that measure the solar neutrino flux (Homestake [6], SAGE [7], GALLEX [8], Kamiokande [9] and SuperKamiokande [10]) find a deficit of 1/2 to 1/3 of the Standard Solar Model prediction [11]. LSND [12], an accelerator experiment, finds evidence forν µ →ν e and ν µ → ν e oscillations, a result that is not excluded by KARMEN [13] and awaits confirmation by MiniBooNE [14]. The current generation of nuclear reactor experiments (Palo Verde [15] and CHOOZ [16]) find null oscillation results and rule outν e →ν x oscillations for ∆m 2 21 > ∼ 10 −3 eV 2 at maximal mixing and sin 2 2 θ 13 > 0.1 for larger ∆m 2 21 (at the 95% confidence level).…”

Neutrino mass matrix suppression by Abelian charges with see-saw mechanism

“…We consider it relatively hopeless to incorporate the neutrino oscillations observed by LSDN [6] which are partly excluded by Karmen 2 [7], especially insofar as in the present article we adopt the philosophy that only particles which are mass protected by the Standard Model (SM) gauge symmetries are sufficiently light to be observed at present. Thus we do not have sterile neutrinos in the model, which we will explain.…”