Capabilities of long-baseline experiments in the presence of a sterile neutrino

TL;DR

This paper investigates how the potential existence of a sterile neutrino impacts the ability of long-baseline experiments to detect CP violation, determine neutrino mass ordering, and identify the source of CP violation, highlighting both challenges and opportunities.

Contribution

It provides a detailed analysis of the effects of sterile neutrinos on long-baseline experiment sensitivities and explores the conditions under which sterile neutrinos can be detected or disregarded.

Findings

Long-baseline experiments can still substantially establish CP violation and mass ordering despite sterile neutrinos.

Sterile neutrinos can significantly alter the sensitivities of long-baseline experiments to key neutrino properties.

Experiments can probe sterile neutrinos differently from short-baseline experiments, offering complementary insights.

Abstract

Assuming that there is a sterile neutrino, we ask what then is the ability of long-baseline experiments to i) establish that neutrino oscillation violates CP, ii) determine the three-neutrino mass ordering, and iii) determine which CP-violating phase or phases are the cause of any CP violation that may be observed. We find that the ability to establish CP violation and to determine the mass ordering could be very substantial. However, the effects of the sterile neutrino could be quite large, and it might prove very difficult to determine which phase is responsible for an observed CP violation. We explain why a sterile neutrino changes the long-baseline sensitivities to CP violation and to the mass ordering in the ways that it does. We note that long-baseline experiments can probe the presence of sterile neutrinos in a way that is different from, and complementary to, the probes of short-baseline experiments. We explore the question of how large sterile-active mixing angles need to be before long-baseline experiments can detect their effects, or how small they need to be before the interpretation of these experiments can safely disregard the possible existence of sterile neutrinos.