Sterile neutrinos beyond LSND at the Neutrino Factory

TL;DR

This paper investigates the potential to detect and constrain light sterile neutrinos at the Neutrino Factory without prior restrictions on their mass and mixing parameters, highlighting the sensitivity of near and long baseline detectors.

Contribution

It presents a comprehensive analysis of sterile neutrino effects at the Neutrino Factory, including sensitivity estimates and the impact of additional detectors, without imposing prior constraints on sterile neutrino parameters.

Findings

Near detectors can probe LSND-motivated m_{41}^2 range.

Long baselines provide sensitivity to atmospheric m^2.

Re-analysis of existing neutrino data could constrain light sterile neutrinos.

Abstract

We discuss the effects of one additional sterile neutrino at the Neutrino Factory. Compared to earlier analyses, which have been motivated by LSND results, we do not impose any constraint on the additional mass squared splitting. This means that the additional mass eigenstate could, with small mixings, be located among the known ones, as it is suggested by the recent analysis of cosmological data. We use a self-consistent framework at the Neutrino Factory without any constraints on the new parameters. We demonstrate for a combined short and long baseline setup that near detectors can provide the expected sensitivity at the LSND-motivated \Delta m_{41}^2-range, while some sensitivity can also be obtained in the region of the atmospheric mass splitting from the long baselines. We point out that limits on such very light sterile neutrinos may also be obtained from a re-analysis of atmospheric and solar neutrino oscillation data, as well as from supernova neutrino observations. In the second part of the analysis, we compare our sensitivity with the existing literature using additional assumptions, such as |\Delta m_{41}^2| \gg |\Delta m_{31}^2| leading to averaging of the fast oscillations in the far detectors. We demonstrate that while the Neutrino Factory has excellent sensitivity compared to existing studies using similar assumptions, one has to be very careful interpreting these results for a combined short and long baseline setup where oscillations could occur in the near detectors. We also test the impact of additional \nu_\tau detectors at the short and long baselines, and we do not find a substantial improvement of the sensitivities.