Search for Active-Sterile Antineutrino Mixing Using Neutral-Current Interactions with the NOvA Experiment.

Area of Science:

• Particle Physics
• Neutrino Physics

Background:

• Neutrino oscillations involve the transformation of one neutrino flavor into another.
• Sterile neutrinos are hypothetical particles that do not interact via the weak nuclear force.
• Accelerator-based experiments provide controlled beams for studying neutrino properties.

Purpose of the Study:

• To conduct the first long-baseline search for sterile antineutrinos.
• To analyze neutral-current interactions in the NOvA detectors.
• To constrain parameters within a 3+1 neutrino mixing model.

Main Methods:

• Utilized the NuMI beam at Fermilab in antineutrino mode.
• Analyzed data from two NOvA detectors at 1 km and 810 km distances.
• Compared observed neutral-current event rates to predictions.

Main Results:

• Observed 121 neutral-current candidates at the far detector, consistent with the prediction of 122±11(stat.)±15(syst.).
• Found no evidence for muon antineutrino to sterile antineutrino oscillation.
• Set the first 3+1 confidence limits using long-baseline accelerator antineutrinos.

Conclusions:

• The results exclude a significant region of parameter space for sterile neutrinos.
• Constrained mixing angles θ24 < 25° and θ34 < 32° at 90% C.L. for 0.05 eV² ≤ Δm41² ≤ 0.5 eV².
• This experiment provides crucial data for understanding neutrino physics beyond the Standard Model.