NOvA

NOvA. The NuMI Off-Axis ν_e Appearance (NOvA) experiment is a long-baseline neutrino oscillation experiment designed to study the properties of these fundamental particles. It consists of two massive particle detectors positioned along a powerful neutrino beam generated at Fermilab in Illinois. By measuring how neutrinos change between their different flavors over a 810-kilometer journey, it probes the parameters of the Pontecorvo–Maki–Nakagawa–Sakata matrix and searches for evidence of CP violation in the lepton sector.

Overview

NOvA is a flagship experiment in the Intensity Frontier program of particle physics, utilizing the upgraded NuMI (Neutrinos at the Main Injector) beamline at Fermilab. The experiment's primary components are a near detector located at Fermilab and a far detector situated in Ash River, Minnesota, near the Canada–United States border. This configuration allows scientists to compare the neutrino beam's composition at its origin and after it has traveled through the Earth's crust, enabling precise measurements of neutrino oscillation phenomena. The collaboration involves hundreds of scientists from institutions across the United States and several other countries, including India, Brazil, and the United Kingdom.

Physics goals

The central physics objectives are to make precision measurements of the mixing angle θ₂₃ and the mass-squared difference Δm₃₂², which govern oscillations between muon neutrino and tau neutrino states. A major goal is to determine the neutrino mass ordering, whether the third mass state is heaviest (normal ordering) or lightest (inverted ordering). Furthermore, it searches for CP violation by comparing oscillations of neutrinos versus antineutrinos, which could help explain the matter–antimatter asymmetry of the universe. The experiment also conducts searches for phenomena beyond the Standard Model, such as sterile neutrinos and non-standard interactions.

Experimental design

The experiment uses a finely segmented, liquid scintillator detector technology. The 300-ton near detector, installed at Fermilab, measures the unoscillated beam composition and flux. The 14-kiloton far detector, the largest plastic scintillator detector in the world, is located off-axis from the NuMI beam centerline to receive a narrower, higher-energy neutrino spectrum ideal for observing electron neutrino appearance. Both detectors are composed of thousands of PVC cells filled with mineral oil-based scintillator and read out by avalanche photodiodes. The neutrino beam is produced by directing protons from Fermilab's Main Injector onto a graphite target, producing pions and kaons that decay to create a muon neutrino beam.

Results and discoveries

NOvA has published significant results constraining oscillation parameters. In 2016, it reported a strong observation of electron neutrino appearance in a muon neutrino beam, a key signature of oscillation. Subsequent data have provided increasingly precise measurements of θ₂₃ and Δm₃₂², though the neutrino mass ordering remains ambiguous. The collaboration has set stringent limits on the existence of light sterile neutrinos and published competitive measurements on antineutrino oscillation parameters. Its data also contribute to the global effort to measure the CP-violating phase δ_CP, with results favoring values that allow for maximal CP violation.

Collaboration and funding

The experiment is operated by the international NOvA collaboration, which includes over 200 scientists and engineers from approximately 50 institutions, including University of Minnesota, University of Cambridge, and Tata Institute of Fundamental Research. Primary funding is provided by the United States Department of Energy through its Office of Science and the National Science Foundation. Significant contributions also come from member institutions' funding agencies in participating countries, such as the Science and Technology Facilities Council in the United Kingdom and the Department of Atomic Energy in India. The far detector facility was constructed on land managed by the United States Forest Service.

Category:Particle physics experiments Category:Neutrino experiments Category:Fermilab