Observation of Prompt Like-Sign Dimuon Production in Neutrino Reactions

Abstract

We report on the observation of twelve like-sign (${\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{\ensuremath{-}}$) neutrino-induced dimuon events with muon momenta greater than 9 GeV. The background from $\ensuremath{\pi}$ and $K$ decay is 1.3 events so that we conclude that this prompt signal is real with a significance greater than 1 in ${10}^{7}$. Although the overall rate is higher than present theoretical estimates, the kinematic distributions of these events are qualitatively consistent with a picture of charm-anticharm production. The ratio of $\frac{{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{\ensuremath{-}}}{{\ensuremath{\mu}}^{\ensuremath{-}}}$ shows a strong energy dependence and rises to (2.5\ifmmode\pm\else\textpm\fi{}1.0) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ at ${E}_{\ensuremath{\nu}}=250$ GeV.