Effect of tau neutrino contribution to muon signals at neutrino factories

TL;DR

This paper examines how tau neutrino contributions impact the precision measurement of atmospheric neutrino oscillation parameters at neutrino factories, revealing that tau contamination worsens measurement accuracy and cannot be easily eliminated.

Contribution

It is the first detailed analysis showing tau contamination's effect on muon signal measurements and the difficulty in removing this background at neutrino factories.

Findings

Tau neutrino contributions increase muon event counts.

Tau contamination reduces the precision of atmospheric parameter measurements.

Removing tau contamination with cuts is ineffective.

Abstract

We discuss precision measurements of the leading atmospheric parameters at a standard neutrino factory with a detector that is sensitive to muons alone. The oscillation of the muon- and electron neutrinos in the neutrino factory beam to tau neutrinos adds to the muon events sample (both right sign and wrong sign) via leptonic decays of the taus produced through charge-current interactions in the detector. In particular, we study how this affects a precision measurement of the atmospheric mixing parameters and the deviation of nu_mu <--> nu_tau mixing from maximality. In spite of the enhancement of the number of events due to the additional tau contribution, the determination of the atmospheric mixing angle and the deviation from maximality will be poorer. We show that it is impossible to devise satisfactory cuts to remove this tau contamination. Neglect of these tau contributions will lead to an incorrect conclusion about the precision obtainable at such a neutrino factory.