DUNE: Next-Gen Underground Neutrino Research

• DUNE is a next-generation, international neutrino research program featuring dual-site facilities and advanced LArTPC detectors deep underground.
• It uses a high-intensity, wide-band neutrino beam from Fermilab to precisely measure oscillations and investigate CP and baryon number violations.
• Its modular detector design enables cutting-edge studies of astrophysical neutrinos and rare event searches, driving breakthroughs in particle physics.

The Deep Underground Neutrino Experiment (DUNE) is a next-generation, international research program in neutrino physics and astroparticle science, centered on a dual-site facility. Using a wide-band, high-intensity neutrino beam produced at the Long-Baseline Neutrino Facility (LBNF) at Fermilab, and a suite of near and far detectors—most prominently, modular liquid argon time projection chambers (LArTPCs) housing a total fiducial mass up to ~70 kt located 1.5 km underground at the Sanford Underground Research Facility (SURF) some 1300 km away—DUNE aims to precisely paper neutrino oscillations, uncover potential sources of CP violation, resolve the neutrino mass hierarchy, search for baryon number violation via nucleon decay, and observe low-energy astrophysical neutrinos from sources such as core-collapse supernovae and the Sun (Collaboration et al., 2015, Kudryavtsev, 2016, Acciarri et al., 2016, Gil-Botella, 19 Dec 2024, Corchado, 10 Oct 2024, Cuesta, 2023, Cuesta, 2023, Collaboration et al., 2020, Collaboration et al., 2022, López, 12 Feb 2025). Advanced LArTPC technology, sophisticated beamline design, and integrated near- and far-site analysis methodologies underpin a diverse program spanning accelerator-based and non-accelerator science.

1. Scientific Goals and Theoretical Framework

DUNE's scientific strategy encompasses three principal pillars: (a) precision measurements of long-baseline neutrino oscillations, (b) searches for rare baryon number violating processes, and (c) detection of low-energy neutrinos from astrophysical sources.

Neutrino Oscillations and CP Violation

The experimental focus is the paper of neutrino oscillations in the three-flavor paradigm, described by the PMNS mixing matrix: $$U_\mathrm{PMNS} = \begin{pmatrix} 1 & 0 & 0 \ 0 & \cos\theta_{23} & \sin\theta_{23} \ 0 & -\sin\theta_{23} & \cos\theta_{23} \end{pmatrix} \begin{pmatrix} \cos\theta_{13} & 0 & e^{-i\delta}\sin\theta_{13} \ 0 & 1 & 0 \ -e^{i\delta}\sin\theta_{13} & 0 & \cos\theta_{13} \end{pmatrix} \begin{pmatrix} \cos\theta_{12} & \sin\theta_{12} & 0 \ -\sin\theta_{12} & \cos\theta_{12} & 0 \ 0 & 0 & 1 \end{pmatrix}$$ where $\theta_{12}$, $\theta_{13}$, $\theta_{23}$ are the mixing angles and $\delta$ is the CP-violating phase. Oscillation probabilities, such as $P(\nu_\mu\to\nu_e)$, are sensitive to $\delta$, the mass-squared splittings $\Delta m_{21}^2$, $\Delta m_{31}^2$, mixing angles, and to coherent forward scattering off electrons in matter (the MSW effect). Long baselines ($L/E \sim 10^3$ km/GeV) amplify matter effects and CP-odd terms, providing unique access to the neutrino mass ordering and potential CP violation in the lepton sector (Collaboration et al., 2015, Kemp, 2017, Gil-Botella, 19 Dec 2024, Abi et al., 2020, Collaboration et al., 2022, López, 12 Feb 2025).

Baryon Number Violation and Nucleon Decay

DUNE's underground LArTPCs possess excellent imaging and particle identification capabilities, enabling efficient searches for nucleon decay channels favored by Grand Unified Theories (GUTs), particularly $p \rightarrow K^+ + \bar{\nu}$, with signal efficiencies around 97% and subdominant backgrounds compared to water Cherenkov detectors (Collaboration et al., 2015, Kudryavtsev, 2016, Gil-Botella, 19 Dec 2024, Collaboration et al., 2020, Collaboration et al., 2022).

Astrophysical Neutrino Detection

DUNE is singularly sensitive to the electron-neutrino ($\nu_e$) component of astrophysical bursts via: $$\nu_e + {}^{40}\mathrm{Ar} \rightarrow e^- + {}^{40}\mathrm{K}^{*}$$ This reaction dominates DUNE’s response to supernova and solar neutrinos, allowing time-resolved studies of flavor, energy, and spectral evolution from core-collapse events. Pinched-thermal flux models,

$$\phi(E_\nu) = \mathcal{N}\left(\frac{E_\nu}{\langle E_\nu\rangle}\right)^{\alpha} \exp[-(\alpha+1) (E_\nu/\langle E_\nu\rangle)],$$

are used for spectral reconstruction and physics extraction (Collaboration et al., 2015, 1804.01877, Cuesta, 2023, Collaboration et al., 2020, Cuesta, 2023, Corchado, 10 Oct 2024). DUNE's deep underground siting (1.5 km, $\sim$4300 m.w.e.) further enhances background suppression for rare events (Kudryavtsev, 2016, Gil-Botella, 19 Dec 2024).

2. Experimental Configuration, Detector Technologies, and Infrastructure

LBNF: High-Intensity Wide-Band Neutrino Beam

The LBNF provides a 1.2 MW ($\to 2.4$ MW upgrade planned) proton beam, producing a high-flux, broadband neutrino beam via pion/kaon decays. The beamline, incorporating proton targetry, multi-horn focusing (with optimized configurations via genetic algorithms), and a $\sim$204 m decay pipe, is designed for both maximal oscillation sensitivity and minimization of systematic uncertainties (Acciarri et al., 2016, Collaboration et al., 2021, Gil-Botella, 19 Dec 2024).

Far Detector: Modular LArTPCs

The far detector complex will comprise four LArTPC modules with a total fiducial mass $\sim$70 kt (Corchado, 10 Oct 2024, Cuesta, 2023, Gil-Botella, 19 Dec 2024). Each LArTPC employs either single-phase (horizontal or vertical drift) or dual-phase technology. In the single-phase design, ionization electrons drift in LAr to wire anode planes, with maximum drift lengths of 3.5–6 m at 500 V/cm; photon detection systems provide precise event timing (Gil-Botella, 19 Dec 2024, Cuesta, 2019, Acciarri et al., 2016). The dual-phase design features extraction of electrons into a gaseous argon phase above the LAr, achieving charge amplification with Large Electron Multipliers (LEMs), enhancing spatial resolution and enabling low (few-MeV) energy thresholds (Cuesta, 2019).

Near Detector Complex and DUNE-PRISM

The near detector (ND), located at Fermilab, provides crucial constraints on flux, cross sections, and interaction models. The ND complex consists of a modular LArTPC (ND-LAr), temporary muon spectrometer (TMS), and a flux monitor (SAND). The PRISM system extends ND capability by physically moving the detector off beam axis (up to 28.5 m), allowing direct sampling of different neutrino energy spectra for model-independent, data-driven extrapolation to the far detector (Hasnip, 17 Jan 2025).

ProtoDUNE Program

Extensive prototyping at the CERN Neutrino Platform (ProtoDUNE-HD, ProtoDUNE-VD, ProtoDUNE-DP; $\sim$700–770 t modules) validates DUNE's technical choices, providing key calibration, high-voltage, cryogenic, and readout studies essential for scale-up (Cuesta, 2019, Gil-Botella, 19 Dec 2024, López, 12 Feb 2025).

3. Accelerator-Based and Astroparticle Physics Methodologies

Oscillation Physics

The appearance and disappearance channels ($\nu_\mu\to\nu_e$, $\nu_\mu\to\nu_\mu$) are reconstructed by combining energy spectra from the ND and FD, with statistical separation of neutrino and antineutrino samples (via magnetic analysis and event topology). Oscillation parameters are extracted through fits involving test statistics such as

$$\Delta\chi^2_{\mathrm{MH}} = \chi^2_{\mathrm{IH}} - \chi^2_{\mathrm{NH}}, \quad \Delta\chi^2_{\mathrm{CPV}} = \min\big[\chi^2(\delta=0) - \chi^2(\delta_\mathrm{true}),\, \chi^2(\delta=\pi) - \chi^2(\delta_\mathrm{true})\big]$$

incorporating systematic uncertainties on flux, cross sections, energy scale, and backgrounds. Tools such as GLoBES, GENIE, and LArSoft are used for simulation and sensitivity studies (Collaboration et al., 2015, Collaboration et al., 2021).

Detection of Rare and Low-Energy Signals

Proton decay searches focus on topologies (e.g. $p\to K^+\bar{\nu}$) where LArTPC d$E$/dx and spatial imaging efficiently identify kaon tracks and decay products at the single-particle level, enabling background suppression to $<0.0012$ events/kt/year (Kudryavtsev, 2016, Gil-Botella, 19 Dec 2024).

Supernova and solar neutrino bursts are detected via continuous data acquisition at low thresholds ($\sim$5 MeV), enabled by deep background shielding and DAQ/trigger innovations. Statistical inference employs forward-folded event spectra using cross section models and spectral parameterizations, as exemplified by: $$N = N_\mathrm{target}\int_{E_\mathrm{min}}^{E_\mathrm{max}} \sigma(E) \Phi(E, t)\, dE$$ for the expected burst event count (1804.01877, Collaboration et al., 2020, Cuesta, 2023, Cuesta, 2023).

BSM Physics

DUNE's broad scope includes sensitivity to:

• sterile neutrino mixing in 3+1 scenarios,
• nonstandard interactions parameterized by $\tilde V_\text{MSW}$,
• heavy neutral leptons via ND decays,
• CPT, Lorentz, and lepton-number violation,
• dark matter via beam-induced and cosmogenic signals,
• and neutrino trident production (Collaboration et al., 2020, Collaboration et al., 2022).

Integrated analyses using the PRISM data, off-axis spectra, and advanced multivariate reconstruction (including CNN-based pattern recognition) are directly targeted at controlling model dependencies and exploring new-physics phase space (Hasnip, 17 Jan 2025, Collaboration et al., 2020).

4. Design, Construction, and Technical Challenges

Scaling the LArTPC to multi-kton volumes drives challenges in argon purity, high-voltage stability ($\sim{-}$180 kV for 3–6 m drifts), field uniformity, and parallelized data acquisition across millions of channels (Acciarri et al., 2016, Gil-Botella, 19 Dec 2024). The experiment adopts a dual-path R&D approach: horizontal-drift and vertical-drift LArTPC designs offer complementary strategies for drift mechanics, photon detection, and modularity (Cuesta, 2023, Gil-Botella, 19 Dec 2024, Cuesta, 2019). Rigorous quality assurance (QA/QC), change control, and ESH protocols are enforced for both detector fabrication and operational safety, incorporating lessons from ProtoDUNE runs (Abi et al., 2020, Gil-Botella, 19 Dec 2024).

Technical innovation also extends to beamline engineering: multi-horn systems, replaceable targets, enhanced radiation control, and grounds for system upgrades to higher MW power are key elements (Acciarri et al., 2016, Collaboration et al., 2021, Gil-Botella, 19 Dec 2024). At the ND, technologies under development include native pixel readout, fine-grained trackers, and advanced calorimetry. The PRISM lateral movement system and its control suite are unique in high-statistics off-axis spectral sampling (Hasnip, 17 Jan 2025).

5. International Collaboration, Project Organization, and Prototyping

DUNE is a large-scale, distributed international project, with governance shared between LBNF (facilities, beam, infrastructure) and the DUNE collaboration (detectors, physics). Consortia dedicated to each detector subsystem take responsibility for R&D, design, fabrication, and integration, with oversight by Technical Coordination bodies and centralized configuration management (Gil-Botella, 19 Dec 2024, Abi et al., 2020, Abi et al., 2020). Early engagement of global partners includes major laboratories and universities across the Americas, Europe (notably CERN), and Asia (Abi et al., 2020, Gil-Botella, 19 Dec 2024).

ProtoDUNE-HD and ProtoDUNE-VD, each ~770-kt, operated at CERN for over 2 years, provide critical validation of the horizontal and vertical drift LArTPC concepts, calibration strategies, and reconstruction algorithms (Gil-Botella, 19 Dec 2024, López, 12 Feb 2025). The 2x2 Demonstrator at Fermilab tests ND design components in realistic beam conditions (López, 12 Feb 2025).

6. Future Prospects and Scientific Impact

DUNE is structured in phases: Phase I encompasses two initial FD modules, a 1.2 MW beam, and a minimal ND suite; Phase II upgrades to four modules (≥40 kt), >2 MW beam, and advanced ND systems (e.g., magnetized high-pressure gaseous argon TPCs, full PRISM capabilities) (Gil-Botella, 19 Dec 2024, Corchado, 10 Oct 2024, López, 12 Feb 2025).

Anticipated outcomes include:

• discovery-level ($\geq 5\sigma$) determination of neutrino mass hierarchy within 1–3 years (Gil-Botella, 19 Dec 2024, López, 12 Feb 2025);
• measurement of δ$_\mathrm{CP}$ with a precision of 6–16$^\circ$ (Gil-Botella, 19 Dec 2024);
• world-leading sensitivity to baryon number violation (proton lifetime limits approaching $1.3 \times 10^{34}$ years in key modes) (Collaboration et al., 2022);
• first observations of the hep solar neutrino flux and high-statistics $\nu_e$ signals from supernovae, including unique time-resolved access to the neutronization burst and accretion/cooling phases (Cuesta, 2023, Corchado, 10 Oct 2024, Cuesta, 2023);
• data-driven control of interaction model uncertainties via PRISM and off-axis ND analysis for sub-percent-level systematics (Hasnip, 17 Jan 2025);
• direct impact on multi-messenger astrophysics, and enhanced global reach for BSM phenomena.

The phased strategy, comprehensive R&D, and robust international collaboration anticipate progressive enhancement in sensitivity, with DUNE positioned as the flagship facility for precision neutrino physics, nucleon decay searches, and astro-neutrino detection well into the coming decades.