Search for Heavy Neutral Leptons in Electron-Positron and Neutral-Pion Final States with the MicroBooNE Detector

Area of Science:

• Particle Physics
• Experimental Neutrino Physics
• Beyond Standard Model Physics

Background:

• Heavy neutral leptons (HNLs) are hypothetical particles beyond the Standard Model.
• Searching for HNLs can shed light on neutrino masses and the early universe.
• Liquid-argon time projection chambers offer unique capabilities for detecting rare particle decays.

Purpose of the Study:

• To perform the first search for HNLs decaying into νe^{+}e^{-} and νπ^{0} final states.
• To set upper limits on the HNL mixing parameter |U_{μ4}|^{2} using MicroBooNE data.
• To probe HNL masses in the MeV range and constrain new physics scenarios.

Main Methods:

• Utilized data from the MicroBooNE detector, a liquid-argon time projection chamber.
• Analyzed data collected synchronously with the NuMI neutrino beam at Fermilab.
• Searched for specific decay signatures (νe^{+}e^{-} and νπ^{0}) within a 7.01×10^{20} protons on target exposure.

Main Results:

• Established upper limits at the 90% confidence level on |U_{μ4}|^{2} for HNL masses between 10-150 MeV (νe^{+}e^{-} channel) and 150-245 MeV (νπ^{0} channel).
• Achieved the most stringent constraints on HNL mixing in the mass range 35-175 MeV.
• Provided the first direct search constraints for the νπ^{0} decay channel.

Conclusions:

• The MicroBooNE experiment has placed significant new constraints on the existence of heavy neutral leptons.
• These results narrow the parameter space for HNLs and motivate further searches.
• The search demonstrates the potential of liquid-argon time projection chambers for exploring beyond Standard Model physics.