The world’s flagship neutrino experiment: how it works

An international team of over 1,000 scientists and engineers from more than 30 countries are building the most advanced neutrino experiment in the world, hosted by the U.S. Department of Energy’s Fermilab. This flagship project is composed of three parts: the Deep Underground Neutrino Experiment (DUNE), the Long-Baseline Neutrino Facility (LBNF) and the Proton Improvement Plan II (PIP-II).

DUNE consists of enormous particle detectors that capture and measure neutrinos, a massive global computing infrastructure to analyze the data and the scientific expertise to translate fleeting electronic signals into world-changing discoveries.

LBNF provides the infrastructure that houses and cools the DUNE detectors and also delivers the neutrino beam from Fermilab.

PIP-II, coupled to the existing Fermilab particle accelerator complex, provides the powerful stream of protons that create the neutrinos for DUNE.

Fermilab’s accelerator complex, improved by PIP-II, will speed protons toward a target housed in new infrastructure built by LBNF. The protons will smash into the target, ultimately decaying into neutrinos that stream first through the DUNE near detector, then through the earth and finally through the DUNE far detector. Data from neutrino interactions collected by the detectors (built in caverns excavated and infrastructure powered by LBNF) will be analyzed by collaborators around the world as they unlock the mysteries of neutrinos.

Deep Underground Neutrino Experiment

DUNE

DUNE is an international collaboration with more than 1,000 scientists and engineers from over 175 institutions, spanning more than 30 countries. Hosted by Fermilab, DUNE is the largest international megascience collaboration based in the United States.

The experiment uses two neutrino detectors built by the DUNE collaboration. The first, called the DUNE near detector, is an underground detector at the experiment’s near site, Fermilab in Batavia, Illinois. After the neutrinos pass through the near detector, they will speed 1,300 kilometers (800 miles) through the earth to the second, much larger detector, called the DUNE far detector, located one mile underground at Sanford Underground Research Facility in Lead, South Dakota. The far detector will be the largest and most technologically advanced liquid-argon neutrino detector in the world, more than 20 times larger than existing detectors of this kind.

Over the 1,300-kilometer separation between the two detectors, neutrinos will morph from one of their three types into another. This process is called neutrino oscillation, and scientists will measure how neutrinos change over this distance from the near to the far detector. The distance between the near and far detector provides maximum sensitivity to the properties scientists want to measure.

Placing the detectors far underground shields them from cosmic rays and other interference at Earth’s surface. Since DUNE scientists will also make measurements of neutrinos that arise from stars and penetrate Earth's surface, the deep underground location is key to blocking as much as possible the arrival of other particles from outer space.

A marvel of engineering, the huge DUNE far detector will be composed of four modules, each as tall and wide as a four-story building and each almost as long as a football field. The modules will be assembled from pieces transported down a mine shaft and assembled like a ship in a bottle.

Combined, the four detector modules will hold nearly 70,000 tons of liquid argon. Argon is an element commonly found in air that is well-suited to studying neutrinos. When a neutrino bumps into an argon atom’s core, it results in a distinctive signal and yields important information about the neutrino interaction. DUNE scientists are currently prototyping two kinds of argon detector — one that uses only liquid argon and a two-phase detector that uses argon as both a liquid and a gas. These ProtoDUNE detectors are currently under construction at CERN, the European particle physics laboratory, which is a partner in LBNF/DUNE.

By comparing how neutrinos change over the course of their 1,300-kilometer journey from Fermilab to the large DUNE detectors, scientists will better understand these mysterious particles and their role in our universe’s evolution.

Learn more about DUNE.

Long-Baseline Neutrino Facility

LBNF

The LBNF project provides the infrastructure for the DUNE experiment. Hosted by Fermilab, LBNF is an internationally designed, coordinated and funded project.

Creating neutrinos from the powerful Fermilab accelerator complex

Fermilab’s accelerators already produce the most intense high-energy beam of neutrinos in the world. LBNF will design and install magnets and neutrino-producing equipment to extract the proton beam from the existing Main Injector accelerator and smash it into a target, producing particles that decay into the neutrinos studied by DUNE.

Excavation and buildings to support the DUNE detectors

LBNF will create the caverns necessary to house the underground DUNE near detector at Fermilab and far detector at Sanford Lab, as well as areas for their assembly and operation. This effort at SURF includes excavating more than 870,000 tons of rock for the mile-deep caverns for the far detector, as well as utilities and surface infrastructure. At Fermilab, the conventional facilities to support the beamline and DUNE near detector include constructing and outfitting support buildings, an underground detector hall, upgrading electrical systems to provide sufficient power, and other supporting infrastructure.

Cryogenic infrastructure to keep detectors supercool

The four far-detector DUNE modules located one mile underground at Sanford Lab will contain 70,000 total tons of cold liquid argon, which must be kept at minus 300 degrees Fahrenheit (minus 184 degrees Celsius) to maintain its liquid state. LBNF will transport that argon underground, supply the cryostats (containers that function like thermoses around the detectors), and build the cryogenics — the pipes, pumps, and other equipment needed to chill, circulate, and purify the liquid argon, as well as liquid nitrogen, which is used for refrigeration.

Learn more about LBNF.

PIP-II

PIP-II

For DUNE to catch lots of neutrinos, it will need to be fed lots and lots of neutrinos. Fermilab's Proton Improvement Plan II, or PIP-II, is the project for making the intense proton beam that will generate vast quantities of neutrinos. PIP-II will be the first particle accelerator built in the United States with significant contributions from international partners.

PIP-II creates the world’s best proton accelerator chain to deliver neutrinos by the boatload to DUNE's two detectors — one on the Fermilab site and one 1,300 kilometers away in South Dakota.

The heart of PIP-II will be the construction of a 250-meter-long superconducting linear accelerator, called SCL (for Superconducting Linac). The linear accelerator, which is scheduled to be completed in 2025, uses the latest superconducting technology to efficiently accelerate a beam of protons to up to 800 million electronvolts. This powerful proton beam from the SCL will gain more energy as it travels through the higher-energy machines of the Fermilab accelerator complex. Once the high-energy beam exits the final accelerator in the chain, more than 1 megawatt of protons will slam into the graphite target of the Long-Baseline Neutrino Facility to produce neutrinos that will then head to the DUNE detectors, where scientists can study the neutrinos in great detail.

The starting point for the powerful proton beam is at the beginning of the SCL. A proton beam will speed down its series of superconducting accelerating cavities — elements that impart energy to the particle beam. Upon exiting SCL, the beam will be steered toward the Booster accelerator, where it is accelerated to 8 billion electronvolts.

From the Booster, the protons will be sent into a larger, circular accelerator complex called the Main Injector-Recycler, a set of 3.3-kilometer-circumference rings that will accelerate the proton beam to even higher energies: 120 billion electronvolts. The beam will then barrel head-on into a block of material called a target.

The protons' collisions with the target will generate other particles that decay into neutrinos which pass through the first DUNE detector, before continuing their journey to the second DUNE detector in the Long-Baseline Neutrino Facility experimental area, 1,300 kilometers (800 miles) away.

Learn more about PIP-II.