Experimental Comparison of Neutrino and Muon Velocities

Abstract

The velocities of neutrinos and muons originating from ${\ensuremath{\pi}}^{+}$ and ${K}^{+}$ decays have been compared using the California Institute of Technology-Fermilab detector in a narrow-band neutrino beam. A time-of-flight comparison between positive muons and neutrinos, as indicated by the final-state negative muons in neutrino interactions, yields $|{\ensuremath{\beta}}_{\ensuremath{\nu}}\ensuremath{-}{\ensuremath{\beta}}_{\ensuremath{\mu}}|<~0.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ (99% confidence level). We assume that $|1\ensuremath{-}{\ensuremath{\beta}}_{\ensuremath{\mu}}|<{10}^{\ensuremath{-}5}$ for these muons.