Catching A Glimpse Of The Most Elusive Particle
Fundamental physics has always relied on a mix of theory and experiments to progress our understanding of the Universe. To this day, one of the most difficult to answer questions is about the fundamental nature of gravity and the forces that direct the Universe. It has long been known that the answer is likely to be found in an elusive and almost impossible-to-study particle: the neutrino.
This is the goal of the megaproject Deep Underground Neutrino Experiment, aka ‘DUNE.’ This is an impressive endeavor spanning multiple states in the US and involves more than 800 miles /1,300 km of underground experiments.
What are Neutrinos?
Neutrinos are an electrically neutral particle with an extremely small mass that has long been thought to be null. Currently, we don’t know at all why neutrinos have mass, except that it seems to work in a different way than for other particles.
What makes neutrinos unique is that they are essentially “ghost” particles,” barely interacting with other forms of matter at all. This is because neutrinos only interact with 2 out of the 4 fundamental forces in the Universe: gravity and weak interaction.
As the weak interaction has a very short range, and gravity barely affects the low-mass neutrinos, neutrinos usually pass through matter without interacting or being slowed down. As a result, neutrinos usually travel at almost the speed of light.
Neutrinos are a fundamental particle that cannot be broken into smaller components and come in 3 variants: electron neutrinos, muon neutrinos, and tau neutrinos. To complicate matters even further, neutrinos seem to regularly shift between these 3 variants.
It is also possible that a 4th exists as well, sterile neutrinos, even harder to detect than the others.
Most neutrinos are produced by nuclear reactions, from nuclear fusions in stars to radioactive decay at the center of the Earth.
Despite their elusiveness, neutrinos are thought to be the most abundant particle in the Universe. Roughly a thousand trillion neutrinos pass through our body every second.
You can learn more about neutrinos on the dedicated website “all things neutrinos” created by the Fermilab.
DUNE’s Design
How do we detect and study a particle traveling at the speed of light when it also doesn’t interact with normal matter? This is the question DUNE is looking to answer.
DUNE will stretch between Fermilab, America’s particle physics and accelerator laboratory in Illinois, and Sanford Underground Research Facility (SURF or Sanford Lab) in South Dakota.
Source: DUNE
The different sites will each have their own specialized task to accomplish.
Fermilab
A proton accelerator called the Proton Improvement Plan-II (PIP-II) is used at the Fermilab site to create a flow of neutrinos. PIP-II is an upgrade on the previous particle acceleration at the Fermilab. It uses superconducting radio-frequency technologies to provide powerful proton beams that, traveling at nearly the speed of light, can be tailored for a diverse set of experiments.
Accelerating structures will be cooled to 2°K (-456°F / -271°C , 2 degrees above absolute zero) in order to provide efficient, high-power, acceleration.
This cooling is achieved thanks to a gigantic, warehouse-sized cooling unit, which is still in construction.
Source: Fermilab
A part of the cooling unit, the cryogenic coldbox, was built in Europe by the CERN and arrived at Fermilab in December 2024.
Source: Fermilab
Fermilab will also have a detector that will record particle interactions near the source of the beam. An 18-meter-high (60-foot-tall) hill was built to slope the beamline on the correct angle to send neutrinos toward South Dakota. The particle beam is aiming downward to take into account the Earth’s curvature and is not stopped by the 800 miles of rocks in between.
Source: Fermilab
Sanford Underground Research Facility (SURF)
SURF will hold the world’s largest neutrino detector of its type ever built. It will use 70,000 tons of liquid argon to catch the neutrino interacting with normal matter.
In total, 4 detector modules will be built, supported by large cryogenic support systems.
Source: Fermilab
This is being built deep underground, 1 mile / 1.5km deep, re-purposing an old gold mine shaft to go deep under and build a massive artificial underground cave.
In total, about 800,000 tons of rock were excavated to create space for the four DUNE far detector modules and the necessary utilities underground. These rocks were dumped into a former mining area.
Source: Fermilab
Together, the Fermilab proton accelerator, detector, and the SURF neutrino detectors form the Long-Baseline Neutrino Facility (LBNF).
What Can DUNE Achieve?
It is always hard to predict exactly what a particle physics experiment will achieve, which is, after all, the whole point. However, we can expect progress on three different topics from the DUNE project.
Origin Of Matter
Since the initial burst of matter and antimatter at the Big Bang, matter has become the dominant particle in the Universe. It is still not really clear why, as both are thought to have been created in equal amounts.
Neutrinos might be the answer. Some physicists think that neutrinos are unique in that they are also their own antiparticles. Others think the shifting of neutrinos between flavors might be the important part. In any case, neutrinos might have tipped the scale toward today’s dominance of matter.
Alternatively, if it has become proven that neutrinos are not responsible, this would mean physicists have to redraw their theories about the origin of the Universe.
Unification Of Forces
The connection between the 4 fundamental forces (electromagnetism, weak nuclear, strong nuclear, and gravity) is still poorly understood.
DUNE could help detect something theorized but never observed experimentally: proton decay.
Physicists today mostly rely on the Standard Model of particle physics. It is a solid framework, but it fails to explain some phenomena and unify the different forces. If measured, proton decay would give us insight into what alternative model would work instead of the theoretical grand unified theories (GUTs), quantum gravity, supersymetry, etc.
Black Holes
Neutrinos are produced in massive quantities during the collapse of stars into black holes. DUNE’s outstanding neutrino detection ability could help us look at what is happening inside neutron stars, and potentially witness the birth of a black hole.
This, in turn, could help us understand better gravity, at both the cosmic and quantum scale.
DUNE’s people
DUNE involves more than 30 countries and 1,000 scientists.
Source: DUNE
It would be impossible to outline the contribution of each scientist to this massive collective project. We can, however, highlight the participation of a few of them:
Pantaleo Raimondi
Source: DUNE
He is the the new project director for the Proton Improvement Plan II, after a lifetime of working on particle accelerators at the CERN, DAFNE, and ESFR.
“Pantaleo joined PIP-II at the right time. As the project wraps up all final design activities, pushes through the procurement phase, and begins detailed integration and commissioning planning, his experience from leading these efforts at ESRF and elsewhere will be invaluable.”
Allan Rowe – PIP-II technical integration manager
Carlo Rubia
A Nobel Laureate and former director of CERN, he first developed the neutrino detection method used by DUNE.
During his mandate, in 1993, “CERN agreed to allow anybody to use the Web protocol and code free of charge … without any royalty or other constraint”.
You can listen to him talking about the DUNE project and other neutrino research projects like ICARUS in this video.
Alexandre Sousa
A specialist in neutrinos, he has a special focus on sterile neutrinos and ” beyond-the-standard-model physics”.
Source: DUNE
“It might not make a difference in your daily life, but we’re trying to understand why we’re here. Neutrinos seem to hold the key to answering these very deep questions.
“With these two detector modules and the most powerful neutrino beam ever we can do a lot of science. DUNE coming online will be extremely exciting. It will be the best neutrino experiment ever.”
Alexandre Sousa on Phys.org
Rising Costs & Timeline
The project’s construction started in 2017, and the first excavation in Dakota began in 2019. The first excavation for the main cavern in Dakota started in 2021.
In August 2024, the prototype detector recorded its first accelerator-produced neutrinos.
Source: DUNE
It has not, however, been a straightforward process. For example, the mine shaft had to be overhauled before rock could be extracted to build the underground caverns, delaying the project and costing at least an extra $300M.
The upgrade on the Fermilab particle accelerator came with another $1B bill. The upgrade also came with a severe incident, with a worker falling 23 feet onto concrete, leading to a half-year interruption of construction until safety procedures could be reviewed.
Overall, the initial project estimates were putting it at a $1.5B price tag and to be finished by 2035. It seems that $3.3B and a 2040 deadline is now more likely. When taking all into account, the project might cost as much as $5B to the American taxpayers.
This has led to some criticism in the press and by non-involved scientists.
“Yeah there’s some noise out there, but the people who are writing those things don’t know what they’re talking about. The early days of a project are always defined by overwhelming optimism that never proves to be true.
James Webb Space Telescope was launched in December 2021 after years of delays and cost overruns, and it now regularly breaks cosmic ground. There’s no remedy like success.”
Ron Ray, DUNE’s deputy project director
However, even with delay and extra costs, giving up on DUNE would mean seeing the US lagging behind the rest of the world in particle physics.
Competition Ramping Up
This is especially the case as 2 other megaprojects in neutrino experimentation are ramping up as well. One in Japan and one in China.
“Anything worth doing involves competition. But this isn’t a simple horse race; neutrino experiments have always involved international collaboration.
Besides, DUNE has additional goals, which include looking for dark matter, the unseen substance that makes up most of the cosmos, and studying neutrinos from the cataclysmic deaths of faraway stars.
Behind the scenes, DUNE scientists have made steady progress toward perfecting the liquid-argon detector, which was still a nascent technology in 2012 when DUNE’s designers gambled on it. I look at the whole list of things that could have turned out differently and it’s like all the stars are aligning.”
Sam Zeller – Physicist at Fermilab
Hyper-Kamiokand
Hyper-Kamiokand, or Hyper-K, is the successor of Super-Kamiokand, which found in 1998 the first strong evidence of neutrinos’ oscillation between neutrino types. Super-Kamiokand was also instrumental in proving neutrinos have mass.
Contrary to DUNE, which is looking at building an entirely new design of neutrino experiment, Hyper-K is more of an upgrade on existing technology. This is likely to help it progress faster, with the beginning of operation as soon as 2027.
This could help it make first a first, rough estimate of the imbalance between neutrinos and antineutrinos.
Hyper-K and Dune might be more partners than competitors, as different neutrino detection methods can help when performing the same measurement. Some specific measurements might also work better on one than the other for technical reasons. As both Japan and the USA have a long history of scientific collaboration, it is likely going to be more of a friendly rivalry between Hyper-K and DUNE.
Jiangmen Underground Neutrino Observatory (JUNO)
In the context of the Great Power competition between the USA and China, JUNO is likely to be seen as a competitor to DUNE.
JUNO holds a first-mover advantage and features a unique experimental design in terms of physics. As an international collaborative project led by China, JUNO will further strengthen China’s leading position in this field.”
Global Times
The detector is made from a 44-meter-deep cylindrical pool in the underground hall buried deep in a granite layer of a hill. Since December 2024, it has been filled with ultra-pure water at the rate of 100 tonnes per hour.
Source: Global Times
This pool harbors the detector, which is equipped with 20,000 photomultiplier tubes of 20 inches and 25,000 photomultiplier tubes of three inches, as well as cables, magnetic shielding coils, light baffles, and other components.
The pool protects the detector from interference by cosmic rays on neutrino detection, as well as natural radioactivity from the surrounding rock.
The liquid injection will occur in two stages. During the first two months, ultra-pure water will fill the spaces inside and outside the acrylic sphere of the central detector. In the following six months, the ultra-pure water inside the sphere will be replaced with a liquid scintillator.
The entire liquid injection process is expected to be completed by August 2025, after which the facility will officially begin operation and data collection.
Global Times
Future Neutrino Projects
DUNE, Hyper-K, and JUNO are the neutrino projects that are already under construction. Others are still in the concept stage but might unlock further understanding of particle physics.
One of them is Enhanced NeUtrino BEams from kaon Tagging (ENUBET), an European project. It will try to detect the charged lepton created each time a neutrino is produced. This could further our understanding of the imbalance between matter and antimatter.
Another is NuTag, using a novel experimental technique: neutrino tagging. This would use a new type of neutrino beamline. This is a design which was already proposed in 1979, but only recently have silicon detectors become able to survive direct exposure to a hadron source beam.
DUNE Conclusion
DUNE is the sort of scientific megaproject that does not appear to have a direct application at first glance. In this, it is very similar to most of the early particle physics and quantum physics sciences of the early 20th century.
This early inquiry into the fundamental aspect of our reality, however, would ultimately produce results required for progress like nuclear power (and bombs), electron microscopy, advanced microchips, satellites, etc.
It is likely that a deeper understanding of neutrinos will have similar long-term results on technological progress, with most advancements decades down the road impossible to guess.
Better understanding neutrinos and how to produce them could also have an array of applications:
Neutrino Company
Neutrino Energy
While rich in potential future applications, neutrino science seems far from being regularly used for commercial applications. This could be changing according to a very ambitious German private startup, Neutrino Energy.
The company is exploring the very novel concept of neutrinovoltaics, or the generation of electricity from the constant flux of neutrinos around us. How this works, is by using a layer of graphene, a 2D material made of carbon (follow the link for a complete explanation of 2D material like graphene or goldene).
This method would convert the thermal (Brownian) motion of graphene atoms into usable electricity, essentially producing energy out of nothing. A similar phenomenon is happening to graphene, with neutrinos “pushing” the atom nuclei, as with argon atoms in the DUNE neutrino detector.
The company has been announcing its upcoming first prototype, called the Powercube, supposed to demonstrate the technology, developed with the assistance of AI.
The company has also been working with the Centre for Materials for Electronics Technology (CMET) in India, aiming “to create a self-charging electric vehicle powered by neutrinovoltaic technology”.
It is hard to tell how close to any commercialization the concept is, as it seems that for now, it is just that, a concept with little reveal about the potential power output or economics. But this is definitely the closest to a “neutrino company” currently on the market.
