The KARMEN time anomaly; status and perspectives

by Guido DREXLIN (FZ Karlsruhe)

Tuesday 23 Nov 1999, 16:30 → 16:45 Europe/Zurich

500/1-001 - Main Auditorium (CERN)

The KARMEN experiment at the pulsed spallation facility ISIS at RAL makes use of neutrinos from the pion-muon decay chain at rest to search for oscillations of muon- to electron-type antineutrinos, as well as to investigate neutrino interactions with nuclei. Analysis of data taken from 1990-95 (KARMEN1) and 97-99 (KARMEN2) show no evidence for oscillations (constraining the allowed LSND parameter space), and experimental CC and NC cross-sections agree with theory. However, a distinct excess of single isolated neutrino events centered around 3.6 microseconds after beam-on-target has been observed, which is called the KARMEN time anomaly. As the probability for a statistical fluctuation is exceedingly small (4.3 sigma effect) and no systematic explanation for the effect has been found, we propose as a working hypothesis that the origin of the 100 excess events observed so far could come from a rare decay of a pion into a muon together with a massive neutral particle X with 33.9 MeV mass. A detailed likelihood analysis of the entire data set for this hypothesis is presented, and prospects for further experimental tests are outlined.

Organiser(s): Jasper Kirkby / EP Division