Tau contamination in the platinum channel at neutrino factories

Abstract

The platinum channel (\nu_e or anti-\nu_e appearance) has been proposed at neutrino factories as an additional channel that could help in lifting degeneracies and improving sensitivities to neutrino oscillation parameters, viz., \theta_{13}, \delta_{CP}, mass hierarchy, deviation of \theta_{23} from maximality and its octant. This channel corresponds to \nu_\mu -> \nu_e (or the corresponding anti-particle) oscillations of the initial neutrino flux, with the subsequent detection of (positrons) electrons from charged current interactions of the (anti-) \nu_e in the detector. For small values of \theta_{13}, the dominant \nu_\mu \to \nu_\tau (or corresponding anti-particle) oscillation results in this signal being swamped by electrons arising from the leptonic decay of taus produced in charge-current interactions of \nu_\tau (anti-\nu_\tau) with the detector. We examine for the first time the role of this tau contamination to the electron events sample and find that it plays a significant role in the platinum channel compared to other channels, not only at high energy neutrino factories but surprisingly even at low energy neutrino factories. Even when the platinum channel is considered in combination with other channels such as the golden (muon appearance) or muon disappearance channel, the tau contamination results in a loss in precision of the measured parameters.