The $\tau$-contamination of the golden muon sample at the Neutrino Factory

Understand

We study the contribution of $\nu_e \to \nu_\tau \to \tau \to \mu$ transitions to the wrong-sign muon sample of the {\em golden} channel of the Neutrino Factory.

• Muons from tau decays are not really a background, since they contain information from the oscillation signal, and represent a small fraction of the sample.
• However, if not properly handled they introduce serious systematic error, in particular if the detector/analysis are sensitive to muons of low energy.
• This systematic effect is particularly troublesome for large $\theta_{13} \geq 1^\circ$ and prevents the use of the Neutrino Factory as a precision facility for large $\theta_{13}$.