Apparent multiple Delta m^2_32 in muon anti-neutrino and muon neutrino survival oscillations from non-standard interaction matter effect

Abstract

Neutrinos propagating through matter may participate in forward coherent neutral-current-like scattering arising from non-standard interactions as well as from the Mikheyev-Smirnov-Wolfenstein matter potential $V_e$. We show that at fixed long baselines through matter of constant density, the non-standard interaction potential $ε_{μτ} V_e$ can contribute an additional term to the oscillation phase whose sign differs for $\anumu$ versus $\numu$ propagation in matter. Its presence can cause different apparent $Δm^2$ to be erroneously inferred on the basis of oscillations in vacuum, with values lying above (for $\anumu$) or below (for $\numu$) the actual $Δm^2_{32}$ for the case where $ε_{μτ}$ is predominantly real-valued and of sign opposite to $Δm_{32}^2$. An NSI scenario invoking only $\Re(ε_{μτ})$ is shown to be capable of accounting for a disparity recently reported between oscillation survival for $\anumu$ and $\numu$ fluxes measured at $735~\mathrm{km}$ by the MINOS experiment. Implications for mantle traversal by atmospheric neutrinos are examined. The NSI matter potential with non-maximal mixing could evade conventional atmospheric neutrino analyses which do not distinguish $\numu$ from $\anumu$ on an event-by-event basis.