DUNE: what detailed argon images and a long baseline can answer

A wide-band beam on a long path through the Earth

DUNE plans to send a neutrino beam from Fermilab to detectors at the Sanford Underground Research Facility in South Dakota, roughly 1,300 kilometers away. The beam will pass through the Earth; no tunnel links the two sites. Over such a long path, matter effects become a substantial part of the measurement.

A wide spread of energies samples several parts of the oscillation pattern at once. Comparing the spectral shapes in neutrino and antineutrino modes helps separate ordering, mixing and CP effects. The price is more demanding reconstruction and modeling than a narrow peak would need.

The goal is one consistent account of neutrino travel that fits every energy range and event class. A sensitivity plot shows what a specified future detector and exposure could distinguish. It is not measured data, and it does not guarantee a discovery date.

Sources: [1] · [2] · [3]

Charge and light give complementary information

In a liquid-argon time projection chamber, charged particles leave a trail of ionization electrons. An electric field drifts these electrons toward readout surfaces. Where they arrive and how long they took to drift together help reconstruct the shape of the interaction in space.

Scintillation light gives the timing, and the charge pattern resolves tracks and showers. Turning drift time into distance needs a start time and calibrations of the field and drift velocity. Diffusion, electrons lost to impurities and field distortions can all alter the recorded image.

An electron shower or a proton track in the image has therefore already passed through the detector’s response. It still has to be classified and turned into an energy estimate. Liquid argon gives detailed images, but the incoming neutrino’s energy is still inferred from the final-state energy that is seen and the energy that is missing.

Sources: [4] · [5] · [6]

A near detector is part of the precision instrument

The near station measures the beam and its interactions with argon before the flavor change over the long baseline. Using argon at both ends means both detectors see the same target nucleus. It does not make the much busier near detector the same as the far detector, which sees sparse events.

Fermilab’s May 2026 description lists a modular liquid-argon near detector, a muon spectrometer that goes with it and a stationary beam monitor. The movable parts are designed to sample spectra at different off-axis angles, and the stationary monitor tracks changes in the beam while they move.

At high rates, interactions overlap, and matching charge with light has to pull them apart. Prototype studies test this matching, the readout and the reconstruction under realistic conditions. These tests support the design; they are not DUNE’s final long-baseline result on CP or ordering.

Sources: [6] · [4]

Construction milestones, with their dates

As of our check on 11 October 2026, DUNE’s far detectors were still under construction. The official milestones list the end of cavern excavation in 2024 and the start of lowering major cryostat steel underground in May 2026. These are completed infrastructure steps; they do not mean a finished far detector has begun physics running.

The February 2026 fact sheet describes parts being produced for the first two of four planned large detector modules, and the cryogenic system is designed to expand in stages. The full design mass, or a sensitivity that assumes four modules, should not be quietly applied to the first stage.

International partners build cryostats, detector parts, electronics and accelerator infrastructure, and assembly, calibration and operation have to bring them together. An excavated cavern, a prototype and a complete instrument are different milestones, even if each is called a major achievement.

Sources: [7] · [2] · [5]

Forecasts depend on exposure and assumptions

The 2020 study of DUNE’s oscillation potential assumed a nominal detector and beam, simulated event selections and specified systematic uncertainties. Its forecasts of discovery over several years hold only under those assumptions. If the schedule slips or the staged detector differs, relabeling the same curve does not fix the forecast.

Future sensitivity depends on the true CP phase and ordering, on the exposure collected and on how well interactions and detector response are understood. With larger samples, systematic uncertainties can matter more. Better near-detector measurements are therefore as important as more far events.

DUNE will also study supernova neutrinos and rare processes such as proton decay. These have different sources, signals and backgrounds from the beam measurement. One versatile instrument serves them all, but each question will still need its own line of evidence.

Sources: [1] · [2] · [4]

Try it in the Lab

Primary sources & revision

1. DUNE Collaboration · Long-baseline oscillation physics potential (2020)
2. Fermilab · DUNE fact sheet (February 2026)
3. Particle Data Group · Neutrino Masses, Mixing, and Oscillations (2024)
4. LBNF/DUNE · Detectors and computing
5. DUNE Collaboration · Far Detector cryogenics infrastructure (2023)
6. Fermilab · Liquid-argon technology both near and far (May 2026)
7. LBNF/DUNE · Milestones

First published 2026-10-11; last revised 2026-10-13. Original explanatory text and diagrams by Sandbox Physics. Illustrations are schematic; no experimental event records are reproduced here. This is an independent educational publication, not an official Nobel or experiment collaboration publication.