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Upper limits for neutrino oscillations muon-antineutrino to electron-antineutrino from muon decay at rest

KARMEN collaboration, B. Armbruster, I. M. Blair, B. A. Bodmann, N. E. Booth, G. Drexlin, J. A. Edgington, C. Eichner, K. Eitel, E. Finckh, H. Gemmeke, J. Hoessl, T. Jannakos, P. Juenger, M. Kleifges, J. Kleinfeller, W. Kretschmer, R. Maschuw, C. Oehler, P. Plischke, J. Reichenbacher, C. Ruf, M. Steidl, J. Wolf, B. Zeitnitz

Abstract

The KARMEN experiment at the spallation neutron source ISIS used \numub from \mup--decay at rest in the search for neutrino oscillations \numubnueb in the appearance mode, with p(\nueb,e+)n as detection reaction of \nueb. In total, 15 candidates fulfill all conditions for the \nueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta)<1.7x10e-3 for Dm^2>100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for \numubnueb.

Upper limits for neutrino oscillations muon-antineutrino to electron-antineutrino from muon decay at rest

Abstract

The KARMEN experiment at the spallation neutron source ISIS used \numub from \mup--decay at rest in the search for neutrino oscillations \numubnueb in the appearance mode, with p(\nueb,e+)n as detection reaction of \nueb. In total, 15 candidates fulfill all conditions for the \nueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta)<1.7x10e-3 for Dm^2>100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for \numubnueb.

Paper Structure

This paper contains 31 sections, 20 equations, 14 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Experimental Configuration
  3. The neutrino source ISIS
  4. The KARMEN detector
  5. Oscillation signature
  6. $\bar{\nu}_{e}$ absorption on protons
  7. Positron signal
  8. Neutron capture signal
  9. Neutron detection efficiency
  10. $\bar{\nu}_{e}$ absorption on carbon
  11. General event requirements
  12. Background reactions
  13. Cosmic induced background
  14. Throughgoing muons
  15. Stopped muons
  16. ...and 16 more sections

Figures (14)

  • Figure 1: (a) Time and (b) energy distribution of neutrinos at the ISIS beam stop for a beam current of $I = 200\,\mu$A: $\bar{\nu}_{\mu}$ from $\mu^{+}$ decay (solid), $\bar{\nu}_{e}$ from $\mu^{-}$ decay (dashed).
  • Figure 2: (a) Front view of the KARMEN detector with details of the central detector region and a single module. (b) Side view, the ISIS target is located to the right.
  • Figure 3: Expected e$^{+}$ signal from p ( $\bar{\nu}_{e}$ , $e^+$ ) n . (a) Visible energy assuming $\hbox{$\Delta m^2$}=1 \ \hbox{eV$^2$}$ (dotted), $10 \ \hbox{eV$^2$}$ (dashed), $100 \ \hbox{eV$^2$}$ (solid) and (b) detection time.
  • Figure 4: (a) Energy and (b) time distribution of neutron capture events. The energy signal (experimental data points) is the sum of p ( n,$\gamma$ ) d (MC dotted line) and Gd ( n,$\gamma$ ) (MC dashed line) capture. The time between neutron production and capture is quasi-exponential with a time constant of $\tau \approx 120$$\mu$s well reproduced by MC.
  • Figure 5: Measured single neutron detection efficiency as a function of time during data taking. The horizontal bars indicate ISIS beam-on intervals, the dotted line shows the neutrino-flux weighted average of the neutron detection efficiency, the dashed lines the total systematic error band.
  • ...and 9 more figures