DUNE

Dune (Deep Underground Neutrino Experiment): Dune is the world's largest international neutrino science experiment located at two sites: A Near Detector will be at the Fermi National Accelerator Laboratory in Batavia, Illinois and four Far Detectors will be at Sanford Underground Research Facility in Lead, South Dakota (SURF). These will be placed in the world's most intense neutrino beam, produced at Fermilab. The Near Detector will record interactions near the neutrino source while the Far Detectors will record their interactions 1300 km downstream. At Fermilab, scientists accelerate and collide protons into a target to generate a powerful neutrino beam that will travel to SURF. Each of the four Far Detectors will have 10,000 tonnes of liquid argon arranged into various detector configurations, and they will measure neutrinos from this beam, as well as from the sun, cosmic-ray interactions in the atmosphere, and from supernovae. DUNE's precision measurements of neutrino oscillations will inform the neutrino mass order and help answer questions about the origin of matter in the universe. It will also seek to measure proton decay, which will test various Grand Unification Theories.

At the European Organization for National Research (CERN), prototypes of these detectors are being constructed. The excavation of enormous caverns at SURF, cryogenics infrastructure, and the neutrino beamline will be provided by the Long Baseline Neutrino Facility. At UCR, we focus on the Far Detectors and modeling backgrounds from radioactivity and cosmic-rays to understand MeV-scale energies.

The Neutrino Beam: Superconducting cavities of the PIP-II particle accelerator will accelerate electrons to 800 MeV. They will travel through a chain of particle accelerators at Fermilab, through the Booster and Main Injector, reaching a total of 120 MeV. Protons then will be extracted from the main injector and collide with a cylindrical graphite rod. This collision will produce muons that can be focused into a tight beam before they decay into neutrinos that will travel through the Earth to SURF. The distance between the Near and Far detectors provides the maximum sensitivity for measuring neutrino oscillations.

DUNE detector module baseline design

Structure of the DUNE Cryostat

Inside the ProtoDUNE detector at CERN

The Far Detectors: The Far Detectors (at SURF) will be the most technologically advanced LAr neutrino detectors in the world. Argon's large size makes interactions more likely and when a neutrino collides with its core, particles are produced that knock electrons loose into the LAr. A high voltage is applied to draw these electrons into wire planes, creating a district signal allowing for 3D reconstruction of the particle's trajectory, yielding important info about neutrino interactions. Tonnes of argon will be piped underground and re-condensed into liquid in the detectors. At SURF, 800,000 tons of rock will be excavated to create space for the four DUNE detector modules. LBNF will carve out 3 long caverns, 2 each containing 2 detectors and the third housing cryogenics equipment and utilities to keep the detectors running.

Excavation began early 2019.

Proposed Low-Background Far Detector Module Design Concept:

Top: The low-background detector is optimized by minimizing the detector components in the bulk of the argon, allowing for good charge and light detection like other LArTPCs. The blue represents external water bricks that are to be nestled in the I-beam support structure to achieve large external neutron reduction. The yellow planes at the top and bottom are charge readout panels copied from the DUNE Far Detector vertical drift module (VD). The central cathode has SiPM modules on the inner part of the cathode plane. The white acrylic box is used to mount reflective WLS foils and SiPM modules. Black points represent SiPM modules mounted in the inside of the acrylic box at a coverage of 10-80%. The beige boxes represent a proposed 2 kTonne fiducial volume (3kTonne is also being considered). This module mostly contains argon other than the small slender support structures for the cathode plane panels.

Middle: Illustrates interactions above 100 keV for neutrons emanating from the stainless steel of the cold cryostat at 2×10-10 neutrons/cm^3/sec for a 1.4 yr exposure.

Bottom: Shows the number of expected solar-neutrino electron-scattering interactions in LAr over threshold for a 3 kTonne-year exposure with contributions from different solar fluxes. Solar neutrinos are much lower energy than typically observed in DUNE, so reconstructing them is quite challenging. When the threshold is reduced to 1 MeV, CNO and pep neutrinos become observable. A threshold of 0.5 allows for the detection of 7Be neutrinos and 0.2 allows for pp neutrinos to be detected. The total number of available neutrinos is 9,000 for a 1 MeV threshold, 130,000 for a 0.5 MeV threshold and 820,000 for a 0.1 MeV threshold.

[Large Low Background kTon-Scale Liquid Argon Time Projection Chambers. https://arxiv.org/abs/2301.11878]

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