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Candidate Events in a Search for Muon Antineutrino to Electron Antineutrino Oscillations

C. Athanassopoulos, L. B. Auerbach, R. Bolton, B. Boyd, R. L. Burman, D. O. Caldwell, I. Cohen, J. B. Donahue, A. M. Eisner, A. Fazely, F. J. Federspiel, G. T. Garvey, M. Gray, R. M. Gunasingha, V. Highland, R. Imlay, K. Johnston, W. C. Louis, A. Lu, J. Margulies, K. McIlhany, W. Metcalf, R. A. Reeder, V. Sandberg, M. Schillaci, D. Smith, I. Stancu, W. Strossman, G. J. VanDalen, W. Vernon, Y-X. Wang, D. H. White, D. Whitehouse, D. Works, Y. Xiao

Abstract

A search for $\nuebar$'s in excess of the number expected from conventional sources has been made using the Liquid Scintillator Neutrino Detector, located 30 m from a proton beam dump at LAMPF. A $\nuebar$ signal was detected via the reaction $\nuebar\,p \rightarrow e^{+}\,n$ with $e^+$ energy between 36 and $60\mev$, followed by a $γ$ from $np\rightarrow dγ$ ($2.2\mev$). Using strict cuts to identify $γ$'s correlated with positrons results in a signal of 9 events, with an expected background of $2.1 \pm 0.3$. A likelihood fit to the entire $e^+$ sample yields a total excess of $16.4^{+9.7}_{-8.9}\pm 3.3$ events, where the second uncertainty is systematic. If this excess is attributed to neutrino oscillations of the type $\numubar\rightarrow\nuebar$, it corresponds to an oscillation probability of ($0.34^{+0.20}_{-0.18}\pm 0.07$)\%.

Candidate Events in a Search for Muon Antineutrino to Electron Antineutrino Oscillations

Abstract

A search for 's in excess of the number expected from conventional sources has been made using the Liquid Scintillator Neutrino Detector, located 30 m from a proton beam dump at LAMPF. A signal was detected via the reaction with energy between 36 and , followed by a from (). Using strict cuts to identify 's correlated with positrons results in a signal of 9 events, with an expected background of . A likelihood fit to the entire sample yields a total excess of events, where the second uncertainty is systematic. If this excess is attributed to neutrino oscillations of the type , it corresponds to an oscillation probability of ()\%.

Paper Structure

This paper contains 1 section, 3 figures, 2 tables.

Table of Contents

  1. Acknowledgements

Figures (3)

  • Figure 1: The distribution of R, the $\gamma$ likelihood parameter. The leftmost bin corresponds to no $\gamma$ found within cuts (R=0), properly normalized in area. (a) Accidental photons (averaged over the tank) and correlated photons (2 methods, described in text). (b) Beam-on minus beam-off spectrum for events in the $36<E_e<60$ MeV energy range. The dashed histogram is the result of the R likelihood fit for events without a recoil neutron, while the solid histogram is the total fit, including events with a neutron.
  • Figure 2: The electron energy distribution, beam-on minus beam-off, for events with an associated 2.2 MeV $\gamma$ with $R>30$. The dashed histogram shows the expected background from known neutrino interactions. The dotted curve is the expected distribution for neutrino oscillations in the limit of large $\Delta m^2$, normalized to the excess between 36 and 60 MeV.
  • Figure 3: The determination of $\sin^22\theta$ vs. $\Delta m^2$ from a maximum likelihood fit to the L/E distribution of the 9 events which satisfy the $R>30$ requirement, where $L/E$ is the neutrino distance to energy ratio, normalized to the oscillation probability extracted from the photon likelihood fit. The shaded area is the allowed region (95% C.L.) from LSND. Not shown is the 20% systematic uncertainty in the LSND normalization. Also shown are 90% C.L. limits from KARMEN (dotted histogram), the BNL E776 experiment (dashed histogram), and the Bugey reactor experiment (dot-dashed histogram).