NOvA experiment

NOvA experiment
Name	NOvA
Collaboration	NOvA collaboration
Location	Fermilab and Ash River, Minnesota
Experiment type	Neutrino oscillation experiment

NOvA experiment. The **NOvA experiment** is a long-baseline neutrino oscillation experiment designed to study the properties of neutrinos, particularly the parameters governing their oscillations between different flavor states. It utilizes a powerful neutrino beam generated at Fermilab and detected at two locations: a near detector on-site and a massive far detector located 810 kilometers away in Ash River, Minnesota. The primary goals include precise measurements of mixing angles, the determination of the neutrino mass ordering, and the search for CP violation in the lepton sector.

Overview

The experiment is a flagship project in the Intensity Frontier of high-energy physics, operating as part of the broader neutrino physics program at Fermilab. It was constructed following the conclusion of the MINOS experiment, leveraging upgraded accelerator facilities like the Main Injector and the NuMI beamline to produce an intense, focused beam of muon neutrinos. The far detector's placement in northern Minnesota provides the long baseline necessary to observe oscillations driven by the atmospheric neutrino mass-squared difference. Data taking began in 2014, with the collaboration involving hundreds of scientists from dozens of institutions across the globe, including key contributions from India, Brazil, and the United Kingdom.

Scientific goals

A central objective is the precise measurement of the mixing angle θ₂₃, one of the parameters in the Pontecorvo–Maki–Nakagawa–Sakata matrix that describes neutrino mixing. The experiment aims to resolve the neutrino mass ordering problem, determining whether the third mass state is heaviest (normal ordering) or lightest (inverted ordering). A major focus is the search for CP violation in neutrinos, which would manifest as a difference in oscillation probabilities between neutrino and antineutrino modes and could help explain the matter-antimatter asymmetry of the universe. Additional physics goals include studies of supernova neutrinos, searches for sterile neutrinos, and investigations of neutrino-nucleus interaction cross-sections.

Experimental design

The design is a classic two-detector, long-baseline configuration to minimize systematic uncertainties. The NuMI (Neutrinos at the Main Injector) beamline at Fermilab produces a muon-neutrino-dominated beam by colliding protons from the Main Injector into a graphite target, then focusing resulting pions and kaons with magnetic horns. The near detector, located 1 km from the target, measures the unoscillated beam composition and flux. The far detector, situated 810 km away at an angle of 14.6 milliradians off-axis, observes the oscillated beam. This off-axis technique selects a narrower band of neutrino energies near the oscillation maximum, enhancing sensitivity to the parameters θ₁₃ and the CP-violating phase δ_CP.

Detectors

Both detectors are functionally identical, segmented liquid scintillator tracking calorimeters, but differ dramatically in scale. They are constructed from extruded polyvinyl chloride cells filled with a mineral-oil-based liquid scintillator and read out via wavelength-shifting fibers connected to avalanche photodiodes. The near detector is a 300-ton compact block used for precise flux measurement and interaction studies. The far detector is a monumental 14,000-ton structure, making it one of the largest particle detectors in the world. Its highly active design and fine granularity allow for excellent identification of final-state particles like electrons, muons, and hadrons, which is crucial for distinguishing between neutrino flavors.

Results and discoveries

The collaboration has produced world-leading measurements, including a precise determination of the mixing angle θ₂₃ and constraints on the neutrino mass ordering. Analyses of electron neutrino appearance and muon neutrino disappearance have significantly improved knowledge of oscillation parameters. While definitive observation of CP violation remains elusive, the data strongly disfavor certain values of the CP-violating phase. The experiment has also published important results on antineutrino cross-sections and set limits on the existence of light sterile neutrinos. Its data continues to be analyzed in combination with results from other experiments like T2K and IceCube.

Collaboration and funding

The **NOvA collaboration** comprises over 200 scientists and engineers from approximately 50 institutions in several countries, including the United States, India, Brazil, the United Kingdom, Czech Republic, and Greece. Primary funding is provided by the United States Department of Energy through its Office of Science, with significant support from the National Science Foundation and international funding agencies like the Science and Technology Facilities Council in the UK and the Department of Atomic Energy (India). Management and infrastructure support are centrally provided by Fermilab, with the far detector site operated in partnership with the University of Minnesota.

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