KATRIN Sensitivity to Sterile Neutrino Mass in the Shadow of Lightest Neutrino Mass
Arman Esmaili, Orlando L. G. Peres
TL;DR
This work assesses KATRIN's sensitivity to a light sterile neutrino within the 3+1 framework by examining distortions in the tritium β-electron endpoint spectrum while treating the active-neutrino mass scale $m_1$ as an unknown parameter. The authors implement an exact four-mass ( $m_1,m_2,m_3,m_4$ ) treatment with $m_2$ and $m_3$ fixed by oscillation data and $|U_{e4}|=\,sinθ_s$, analyzing the spectrum via a detailed χ^2 across 31 retarding potentials and optimizing run times. They demonstrate that after 3 years, KATRIN can reach sensitivities of $\\sin^2(2θ_s) \\sim 10^{-2}$ and that the sensitivity to $Δm^2_{41}$ depends on $m_1$, with potential to set the strongest limits on $Δm^2_{41}$ for small mixing. The study finds a notable interplay between $m_1$, $m_4$, and $|U_{e4}|$, and situates KATRIN's reach relative to prior short-baseline analyses, while acknowledging cosmological constraints on larger $m_1$ values.
Abstract
The presence of light sterile neutrinos would strongly modify the energy spectrum of the Tritium β-electrons. We perform an analysis of the KATRIN experiment's sensitivity by scanning almost all the allowed region of neutrino mass-squared difference and mixing angles of the 3+1 scenario. We consider the effect of the unknown absolute mass scale of active neutrinos on the sensitivity of KATRIN to the sterile neutrino mass. We show that after 3 years of data-taking, the KATRIN experiment can be sensitive to mixing angles as small as sin^2 (2θ_s) ~ 10^-2. Particularly we show that for small mixing angles, sin^2 (2θ_s) < 0.1, the KATRIN experiment can gives the strongest limit on active-sterile mass-squared difference.