Results from the Palo Verde neutrino oscillation experiment

Creators: Boehm, F.; Busenitz, J.; Cook, B.; Gratta, G.; Henrikson, H.; Kornis, J.; Lawrence, D.; Lee, K. B.; McKinny, K.; Miller, L.; Novikov, V.; Piepke, A.; Ritchie, B.; Tracy, D.; Vogel, P.; Wang, Y.-F.; Wolf, J.

Abstract

The ν̅e flux and spectrum have been measured at a distance of about 800 m from the reactors of the Palo Verde Nuclear Generating Station using a segmented Gd-loaded liquid scintillator detector. Correlated positron-neutron events from the reaction ν̅ep→e+n were recorded for a period of 200 d including 55 d with one of the three reactors off for refueling. Backgrounds were accounted for by making use of the reactor-on and reactor-off cycles, and also with a novel technique based on the difference between signal and background under reversal of the e+ and n portions of the events. A detailed description of the detector calibration, background subtraction, and data analysis is presented here. Results from the experiment show no evidence for neutrino oscillations. ν̅e→ν̅x oscillations were excluded at 90% C.L. for Δm2>1.12×10-3 eV2 for full mixing and sin22θ>0.21 for large Δm2. These results support the conclusion that the observed atmospheric neutrino oscillations do not involve νe.

Additional Information

©2000 The American Physical Society Received 16 March 2000; published 7 September 2000 We would like to thank the Arizona Public Service Company for the generous hospitality provided at the Palo Verde plant. The important contributions of M. Chen, R. Hertenberger, K. Lou, and N. Mascarenhas in the early stages of this project are gratefully acknowledged. We thank K. Scholberg for illuminating discussions on the Super-Kamiokande three flavor analysis. We are indebted to J. Ball, B. Barish, R. Canny, A. Godber, J. Hanson, D. Michael, C. Peck, C. Roat, N. Tolich, and A. Vital for their help. We also acknowledge the generous financial help from the University of Alabama, Arizona State University, California Institute of Technology, and Stanford University. Finally, our gratitude goes to CERN, DESY, Fermilab, LANL, LLNL, SLAC, and TJNAF who at different times provided us with parts and equipment needed for the experiment. This project was supported in part by the Department of Energy. One of us (J.K.) received support from the Hungarian OTKA fund and another (L.M.) from the ARCS Foundation.

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