Golden channel at a neutrino factory revisited: Improved sensitivities from a magnetized iron neutrino detector

This paper describes the performance and sensitivity to neutrino mixing parameters of a Magnetised Iron Neutrino Detector at a Neutrino Factory with a neutrino beam created from the decay of 10 GeV muons. Specifically, it is concerned with the ability of such a detector to detect muons of the opposite sign to those stored (wrong-sign muons) while suppressing contamination of the signal from the interactions of other neutrino species in the beam. A new, more realistic simulation and analysis, which improves the efficiency of this detector at low energies, has been developed using the GENIE neutrino event generator and the GEANT4 simulation toolkit. Low-energy neutrino events down to 1 GeV were selected, while reducing backgrounds to the ${10}^{\ensuremath{-}4}$ level. Signal efficiency plateaus of $\ensuremath{\sim}60%$ for ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and $\ensuremath{\sim}70%$ for ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ events were achieved starting at $\ensuremath{\sim}5\text{ }\text{ }\mathrm{GeV}$. Contamination from the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ oscillation channel was studied for the first time and was found to be at the level between 1% and 4%. Full response matrices are supplied for all the signal and background channels from 1 GeV to 10 GeV. The sensitivity of an experiment involving a Magnetised Iron Neutrino Detector detector of 100 ktons at 2000 km from the Neutrino Factory is calculated for the case of ${sin}^{2}2{\ensuremath{\theta}}_{13}\ensuremath{\sim}{10}^{\ensuremath{-}1}$. For this value of ${\ensuremath{\theta}}_{13}$, the accuracy in the measurement of the $CP$-violating phase is estimated to be $\ensuremath{\Delta}{\ensuremath{\delta}}_{CP}\ensuremath{\sim}3\ifmmode^\circ\else\textdegree\fi{}--5\ifmmode^\circ\else\textdegree\fi{}$, depending on the value of ${\ensuremath{\delta}}_{CP}$, the $CP$ coverage at $5\ensuremath{\sigma}$ is 85% and the mass hierarchy would be determined with better than $5\ensuremath{\sigma}$ level for all values of ${\ensuremath{\delta}}_{CP}$.