NOvA's Current and Future Sterile Neutrino Searches

TL;DR

The NOvA experiment undertakes a sterile neutrino search in the 3+1 framework using both ND and FD data from the NuMI beam, analyzing νμ CC and NC channels to look for oscillations into a sterile state characterized by $Δm^2_{41}$. The study reports world-leading limits on $sin^2θ_{24}$, $sin^2θ_{34}$, and $sin^2θ_{μτ}$ across $Δm^2_{41}$ in the range $10^{-3}$–100 eV^2, with results consistent with three-flavor oscillations. To improve sensitivity in the higher $Δm^2_{41}$ region where systematics dominate, NOvA plans to incorporate data from the Booster Neutrino Beam, including a ν-on-e sample as an in-situ flux constraint and to exploit the off-axis BNB configuration. Initial BNB studies indicate a ~30% sensitivity gain when combined with NuMI data, and the approach promises broader utility for on-axis sterile searches and cross-section constraints.

Abstract

The NOvA experiment's most recent search for eV-scale sterile neutrinos under a 3+1 model simultaneously analyses muon neutrino and neutral current datasets from the NuMI beam at its Near ($\sim$\qty{1}{km} baseline) and Far (\qty{810}{km} baseline) detectors to look for oscillations consistent with a sterile neutrino. The analysis is systematically limited in the region of parameter space where $Δm^2_{41} \gtrsim 1~\mathrm{eV}^2$. This region of parameter space is preferred by sterile neutrino interpretations of current experimental anomalies and so improving sensitivity here is high-priority. These proceedings present our current search strategy, and discusses future plans to include data from a second beamline, the Booster Neutrino Beam, to improve our sensitivity in systematics-dominated regions of parameter space.

Figures (7)

• Figure 1: Oscillation probabilities as a function of $L/E$ for NC (left) and muon neutrino (right) disappearance under three-flavour oscillations (black) and with oscillations under a 3+1 model with varying values of $\Delta m^2_{41}$. The shaded grey background corresponds to where the NOvA data lay in the ND, at low $L/E$ and in the FD, at higher $L/E$.
• Figure 2: 90% confidence level exclusion limits for NOvA's 2025 sterile neutrino analysis PhysRevLett.134.081804, presented in terms of $\Delta m^2_{41}$, and $\sin^2\theta_{24}$, $\sin^2\theta_{34}$, and $\sin^2\theta_{\mu\tau} = \sin^22\theta_{24}\sin^2\theta_{34}$, and compared with results from other experiments. The limits are world-leading in several regions of parameter space.
• Figure 3: Schematic showing the layout of the two neutrino beams provided by Fermilab, the BNB and NuMI, along with the three currently operating neutrino oscillation experiments. The NOvA ND can see neutrinos from the BNB at an off-axis angle of around 160mrad (9.2°).
• Figure 4: Plot of mean time of each reconstructed "slice" in BNB triggered NOvA readout using a subset of the data taken. The peak beginning at 319.4 corresponds to the expected BNB arrival time, with the width of the distribution corresponding to the expected 1.6 beam arrival time distribution. Backgrounds are from cosmic rays.
• Figure 5: BNB neutrino flux at NOvA ND, separated by neutrino flavour (left), neutrino parent (right). The beam is primarily muon neutrinos, with subdominant contributions from muon neutrinos, electron neutrinos and electron antineutrinos. The beam is dual-peaked with the low-energy peak coming from neutrinos produced in $\pi$ decay, and the high-energy peak coming from neutrinos produced in $K$ decay.