The sensitivity of DUNE: the most sophisticated underground experiment to hunt neutrinos in the world

A spider web, the perfect trap, is so sensitive that it only takes the leg of a millimeter-sized insect to brush it for the predator to know the exact size and position of the tiny prey.

DUNE is the most technologically sophisticated “spider web” that humans can generate. The “prey” to be hunted are particles so small that the insects are, next to them, mythological giants.

Intercept elusive neutrinos

DUNE will intercept neutrinos, particles whose mass is at least a million times less than that of the electron. Sixty-six billion neutrinos pass through every square centimeter of skin of each person on Earth every second, and we do not notice them because only one neutrino in every 10 trillion is trapped when passing through the earth. However, they are so important that, in a scientific collaboration, we are launching a network, the most advanced experiment of the many that exist to hunt, characterize and understand them.

The name of the experiment, in which we collaborate from CIEMAT, is DUNE. Stay with him. The DUNE neutrino experiment (Deep Underground Neutrino Experiment) is the most important particle accelerator-based megaproject after the LHC.

And for what? Why do we want to hunt neutrinos? We do it because we think it is the particle that can answer a fundamental question, as philosophical as it is scientific: how was the universe we know today possible? How is it possible that we exist?

DUNE will have a unique sensitivity to make discoveries in particle physics. The macroexperiment is designed to explain the origin of matter (of all matter); to search for new physics, and to detect neutrinos from astrophysical phenomena, whether from a supernova explosion or from the sun.

This is the inside of protoDUNE, an experimental program to test and validate the technologies and design that will be applied to the construction of the DUNE Far Detector at the Sanford Underground Research Facility (SURF).

What are neutrinos?

Neutrinos are the most abundant elementary particles after photons, but the ones that fit the worst within the Standard Model, the “Bible” of physics.

They are much lighter than the rest of the particles, so they tend to escape from the detectors, and their mass has not yet been able to be measured accurately. Additionally, they have no charge, making the difference from their antimatter counterpart, antineutrinos, unclear.

However, being so elusive has its advantages. Neutrinos are excellent messengers of astrophysical phenomena and, when detectors capture them, they provide direct information about the source that originates them. They are capable of traveling enormous distances, crossing any element of space.

Its relationship with the origin of matter

After the big Bang, the universe was filled with equal amounts of matter and antimatter, which annihilated as it cooled. However, about one in every 10 billion particles of matter survived and created stars, galaxies, and life on Earth.

We do not know what made it possible for that small piece of matter to thrive, but it was necessary for us to exist.

To figure out what happened, we have to explain why matter and antimatter particles behave differently. Discovering a different behavior between neutrinos and antineutrinos could provide the key to why the excess matter was created, since we already know that the behavior of other particles cannot explain it.

At DUNE we will study the interactions of neutrinos and antineutrinos in the detectors to better understand the changes that these particles undergo when they travel from one point to another. This will help explain what could have happened right after the big Bang: why the matter triumphed.

Those that come from supernovae

DUNE will also be sensitive to astrophysical neutrinos produced in supernova explosions or the Sun.

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Astronomers combined observations from three different observatories (Atacama Large Millimeter/submillimeter Array, red; Hubble, green; Chandra X-ray Observatory, blue) to produce this colorful multi-wavelength image of the intricate remains of Supernova 1987A.
NASA, ESA, A. Angelich (NRAO, AUI, NSF)

During a supernova explosion, 99% of the star’s energy is released in the form of neutrinos, which are the first capable of escaping its core. These supernova neutrinos are emitted in a burst lasting a few tens of seconds.

The first and only supernova neutrinos were detected in 1987 when a star collapsed in the Large Magellanic Cloud. Two experiments then detected a few dozen neutrinos a few hours before the light from the explosion reached Earth.

DUNE will have a much higher sensitivity and will be able to detect several thousand neutrinos from a supernova exploding in the Milky Way. Additionally, DUNE will be the only operating experiment with sensitivity to neutrinos emitted in the first phase of a supernova explosion.

Thanks to this, we will be able to know the collapse mechanism of the supernova core and we will have new information about particle physics.

Finally, DUNE will be sensitive to searches for new physics beyond the standard model, such as the decay of the proton and other nucleons, new types of neutrinos, and even dark matter.

What is the DUNE experiment?

The idea is to create and propel neutrinos and antineutrinos from a laboratory – Fermilab – in Batavia, Illinois (United States) and detect them when they arrive at a similar facility – Sanford Underground Research Facility (SURF) – in Lead, South Dakota , after a journey of 1,300 kilometers. Something like going from Madrid to Paris underground, at a speed of approximately 99.9% of the speed of light, about 299,338 kilometers per second.

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In DUNE, the neutrinos will be produced in a proton accelerator at Fermilab and a nearby detector will characterize them to compare them with what was measured in the distant detector at the Sanford Underground Research Facility once they have traveled 1,300 km. .
Fermilab, CC BY

A detector close to the point of production will characterize the neutrinos at their starting point. And a distant detector located in an old gold mine 1,500 m underground, at SURF, will capture them to study changes in their properties.

To achieve such sensitivity, DUNE detectors require the development of cutting-edge technology. At SURF, four large detectors will be built, 4 stories high, containing 67,000 tons of liquid argon below the surface, equivalent to more than 15 Olympic swimming pools at -190ºC. These immense pools will allow neutrinos to be trapped.

In the interaction of the particles with argon, charged particles are emitted, which are captured thanks to important electric fields. But also small amounts of light, collected by sensors capable of capturing quantities as tiny as a single photon.

file 20231207 15 wdefv9.png?ixlib=rb 1.1
This is a real image of particles interacting in liquid argon in ProtoDUNE.

Pilot test at CERN

Building the powerful DUNE detectors is a great challenge and, to address it, you must prove that you have the necessary technology, since such large liquid argon detectors have never been built.

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The house-sized ProtoDUNE test detectors were assembled and tested at CERN in Europe. They were filled with hundreds of tons of liquid argon.
Fermilab, CC BY

With this objective, in Geneva, at the headquarters of CERN (European Organization for Particle Physics, one of the largest entities participating in the project), two large DUNE prototypes have been built, in which the technology is being finalized. .

At the end of this decade we will have the first data from DUNE. With them will come more answers and, I’m sure, more questions.

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