Final results from the Palo Verde neutrino oscillation experiment

Abstract

The analysis and results are presented from the complete data set recorded at Palo Verde between September 1998 and July 2000. In the experiment, the ${\overline{\ensuremath{\nu}}}_{\mathrm{e}}$ interaction rate has been measured at a distance of 750 and 890 m from the reactors of the Palo Verde Nuclear Generating Station for a total of 350 days, including 108 days with one of the three reactors off for refueling. Backgrounds were determined by (a) the $\mathrm{swap}$ technique based on the difference between signal and background under reversal of the positron and neutron parts of the correlated event, and (b) making use of the conventional reactor-on and reactor-off cycles. There is no evidence for neutrino oscillation and the mode ${\overline{\ensuremath{\nu}}}_{\mathrm{e}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{x}$ was excluded at 90% C.L. for $\ensuremath{\Delta}{m}^{2}>1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3} {\mathrm{eV}}^{2}$ at full mixing, and ${\mathrm{sin}}^{2}2\ensuremath{\theta}>0.17$ at large $\ensuremath{\Delta}{m}^{2}.$