Measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>L</mml:mi><mml:mo>/</mml:mo><mml:mi>E</mml:mi></mml:math>distributions of atmospheric<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>ν</mml:mi></mml:math>in Soudan 2 and their interpretation as neutrino oscillations

A deficit of atmospheric ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ events, consistent with the hypothesis of neutrino oscillations, is observed in the 5.90 kiloton-year fiducial exposure of the Soudan 2 detector. An unbinned maximum likelihood analysis of the neutrino $L/E$ distribution has been carried out using the Feldman-Cousins prescription. The probability of the no oscillation hypothesis is $5.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}.$ The 90% confidence allowed region in the ${\mathrm{sin}}^{2}2\ensuremath{\theta},\ensuremath{\Delta}{m}^{2}$ plane is presented. The region includes the 90% confidence allowed region of the Super-K experiment.