New limit on the strength of mixing betweenνμandνe

Abstract

Measurements have been made of the reactions ${\nu }_e$n→$e^{\mathrm{-}}$p and ${\nu }_{\mu }$n→${\mu }^{\mathrm{-}}$p in a detector located an effective distance of 96 m from a neutrino source. These measurements yield directly the energy-dependent ratio of the neutrino fluxes [Φ(E(${\nu }_e$))/Φ(E(${\nu }_{\mu }$ ${\left)\right)]}_{\mathrm{obs}}$ incident on the detector. When combined with an estimate of the flux ratio emanating from the source [Φ(E(${\nu }_e$))/Φ(E(${\nu }_{\mu }$ ${\left)\right)]}_{\mathrm{calc}}$, the measured ratio provides an upper limit on the strength of mixing between ${\nu }_{\mu }$ and ${\nu }_e$. We obtain ${\sin }^2$2α<3.4×${10}^{\mathrm{-}3}$ (90% C.L.) in the limit of large mass difference Δ$m^2$ (≡‖$m_1$ ${}^2$-$m_2$ ${}^2$‖) between neutrino mass eigenstates, $m_1$ and $m_2$; and an upper limit on the product Δ$m^2$ sin2α<0.43 ${\mathrm{eV}}^2$ in the limit of small mass difference.