Fermilab offers students chance to learn about STEM careers

On Feb. 26, a crowd of engineers, technicians and analysts crowded around a computer screen as Fermilab scientist Deborah Harris pressed “stop” on the data collection for the MINERvA neutrino experiment.

“We’re all just really excited by what we’ve accomplished,” said Harris, MINERvA co-spokesperson and future professor at York University. “The detector worked wonderfully, we collected the data we need, and we did it on schedule.”

MINERvA studies how neutrinos and their antimatter twins, antineutrinos, interact with the nuclei of different atoms. Scientists use that data to help discover the best models of these interactions. Now, after nine years of operation, the data taking has come to an end, but the analysis will continue for a while. MINERvA scientists have published more than 30 scientific papers so far, with more to come. As of today, 58 students have obtained their master’s or Ph.D. degrees doing research with this experiment.

Neutrinos could hold the answer to one of the most pressing mysteries in physics: why matter was not completely annihilated by antimatter after the Big Bang. That imbalance from 13.7 billion years ago led the universe to develop into what we see today. Studying neutrinos (and antineutrinos) could uncover the mystery and help us understand why we are here at all.

A number of neutrino experiments investigate this mystery, including Fermilab’s NOvA experiment and the upcoming international Deep Underground Neutrino Experiment, hosted by Fermilab. To be as successful as possible, these experiments need precise models that describe what happens before and after a neutrino collides with an atom.

Every time a neutrino collides with part of an atom inside a detector, a spray of new particles flies off and travels through the rest of the detector. In order to understand the nuances of neutrinos, scientists need to know the energy of the neutrino when it first enters the detector and the energy of all the particles produced after the interaction. This task is complicated by the fact that some of the outgoing particles are invisible to the detector — and must still be accounted for.

Imagine you’re playing pool and you shoot the cue ball at another ball. You can easily predict where that second ball will go. That prediction, however, gets much more complex when your cue ball strikes a collection of balls. After the break shot, they scatter in all directions, and it’s hard to predict where each will go. The same thing is true when a neutrino interacts with a lone particle: You can easily predict where the lone ball will go. But when a neutrino interacts with an atom’s nucleus — a collection of protons and neutrons — the calculation is much more difficult because, like the pool balls, particles may go off in many different directions.

“It’s actually worse than that,” said Kevin McFarland, former MINERvA co-spokesperson and professor of physics at the University of Rochester. “All the balls in the break shot are also connected by springs.”

MINERvA provides a neutrino-nucleus interaction guidebook for neutrino researchers. The experiment measured neutrino interactions with polystyrene, carbon, iron, lead, water and helium. Without MINERvA’s findings, researchers at other experiments would have a much tougher time understanding the outcomes of these interactions and how to interpret their data.

“I really am proud of what we’ve been able to accomplish so far,” said Laura Fields, Fermilab scientist and co-spokesperson for MINERvA. “Already the world has a much greater understanding of these interactions.”

The idea for the experiment was first submitted to Fermilab in 2002 by two separate groups — one helmed by Fermilab scientist Jorge Morfin and one by McFarland. Bringing the two ideas together enriched the experiment as a whole and ultimately gave rise to MINERvA.

From conception to construction to data collection, the MINERvA collaboration actively recruited international participation in the experiment, encouraging contributions from numerous students and collaborators from around the world – including two institutes in India and five in Latin America (Brazil, Chile, Mexico, Peru) – to bring the experiment to life. MINERvA has welcomed 41 Latin American students and four Indian students, 30 of whom have completed advanced degrees.

“It’s been a wonderful experience,” said Morfin, former co-spokesperson for MINERvA. “It’s been a successful program for the students, and for all of MINERvA.”

MINERvA started collecting data in early 2010. In 2012, scientists working on MINERvA completed their first data set, allowing them to publish their initial findings. Following that, Fermilab increased its particle beam intensity, which increased the number of neutrinos available to MINERvA. As a result, the collaboration collected 10 times the amount of data compared to the previous run. Now MINERvA has officially completed its data acquisition.

But the work isn’t done.

“We still have a lot of data to analyze,” Fields said. “Completing our run was a celebration of MINERvA’s past and, more importantly, a look towards the future of MINERvA’s science and physics as a whole.”

Visit the MINERvA website. This work is supported by the U.S. Department of Energy Office of Science.

The Dark Energy Spectroscopic Instrument seeks to further our cosmic understanding by creating the largest 3-D map of galaxies to date. Below is a press release issued by Lawrence Berkeley National Laboratory announcing first light for the optical lenses of this extraordinary instrument. The U.S. Department of Energy’s Fermi National Accelerator Laboratory is a key player in the construction of this instrument, drawing on more than 25 years of experience with the Sloan Digital Sky Survey and the Dark Energy Survey.

Fermilab contributed key elements to DESI, including the corrector barrel, hexapod and cage. The corrector barrel – designed, built and initially tested at Fermilab – aligns DESI’s six large lenses to within the accuracy of the width of a human hair. This precision is essential to ensure that the images DESI collects are sharp and clear. The hexapod, designed and built with partners in Italy, moves and focuses the lenses. Both the barrel and hexapod are housed in the cage, which was also designed and built by Fermilab. Additionally, Fermilab carried out the testing and packaging of the charge-coupled devices, or CCDs. The CCDs convert the light passing through these lenses from distant galaxies into digital information that can then be analyzed by the collaboration.

Fermilab also provided other components to the project, including the online databases used for data acquisition and the software that will ensure that each of the 5,000 robotic positioners are precisely pointing to their celestial targets.

“DESI promises to be at the core of the next decade of cosmological discoveries,” said Liz Buckley-Geer, a Fermilab scientist and a member of the DESI collaboration. “It’s an amazing project to be a part of, and we’re celebrating this moment with the entire DESI team.”

On April 1 the dome of the Mayall Telescope near Tucson, Arizona, opened to the night sky, and starlight poured through the assembly of six large lenses that were carefully packaged and aligned for a new instrument that will launch later this year.

Just hours later, scientists produced the first focused images with these precision lenses – the largest is 1.1 meters in diameter – during this early test spin, marking an important “first light” milestone for the Dark Energy Spectroscopic Instrument, or DESI. This first batch of images homed in on the Whirlpool Galaxy to demonstrate the quality of the new lenses.

”It was an incredible moment to see those first images on the control room monitors,” said Connie Rockosi, who is leading this early commissioning of the DESI lenses. “A whole lot of people have worked really hard on this, and it’s really exciting to show how much has come together already.”

This phase of the project will continue for about six weeks and will require the efforts of several onsite scientists and remote observers, noted Rockosi, a professor of astronomy and astrophysics at UC Santa Cruz.

When completed later this year, DESI will see and measure the sky’s light in a far different way than this assembly of lenses. It is designed to take in thousands of points of light instead of a single, large picture.

The finished DESI will measure the light of tens of millions of galaxies reaching back 12 billion light-years across the universe. It is expected to provide the most precise measurement of the expansion of the universe and provide new insight into dark energy, which scientists explain is causing this expansion to accelerate.

DESI’s array of 5,000 independently swiveling robotic positioners, each carrying a thin fiber-optic cable, will automatically move into preset positions with accuracy to within several microns (millionths of a meter). Each positioner is programmed to point its fiber-optic cable at an object to gather its light.

That light will be channeled through the cables to a series of 10 devices known as spectrographs that will separate the light into thousands of colors. The light measurements, known as spectra, will provide detailed information about objects’ distance and the rate at which they are moving away from us, providing fresh insight about dark energy.

DESI’s lenses are housed in a barrel-shaped device known as a corrector that is attached above the telescope’s primary mirror, and the corrector is moved and focused by a surrounding device known as a hexapod.

Fermi National Accelerator Laboratory (Fermilab) researchers led the design, construction and initial testing of the corrector barrel, hexapod and supporting structures that hold the lenses in alignment.

“Our entire team is pleased to see this instrument achieve first light,” said Gaston Gutierrez, the Fermilab scientist who managed this part of the project. “It was a great challenge building such large devices to within the precision of a hair. We’re happy to see these systems come together.”

The giant corrector barrel and hexapod, which together weigh about 5 tons, must maintain alignment with the telescope’s large reflector mirror that is 12 meters below, all while compensating for the movement of the telescope’s assemblage of massive components as it swings across the sky.

“This is a big step up. It’s a leap into the future for the Mayall Telescope that will enable exciting new scientific discoveries,” said Michael Levi, DESI’s director and a physicist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution in the international DESI collaboration. “The team has been working on the new corrector for the past five years, so it was quite an experience seeing $10 million of optics lifted by the crane during installation.”

The new set of lenses expands the telescope’s viewing window by about 16 times, enabling DESI to map about one-third of the visible sky several times during its five-year mission.

Peter Doel, a professor at University College London, led the team that designed the new optical system. “We had a half-dozen vendors involved with making and polishing the glass. One mistake would have spoiled everything. It’s thrilling to know that they survived the journey and work so well.”

“This was kind of the moment of truth,” said David Schlegel, a DESI project scientist. “We have been biting our nails.”

David Sprayberry, the National Optical Astronomy Observatory (NOAO) site director at Kitt Peak, said, “We have an amazing, multitalented team to make sure that everything is working properly,” including engineers, astronomers and telescope operators working in shifts. NOAO operates the Mayall Telescope and its Kitt Peak National Observatory site.

He noted the challenge in updating the sturdy, decades-old telescope, which started up in 1973, with high-precision equipment. “Ultimately we must make sure DESI can target to within 5-micron accuracy – not much larger than a human hair,” he said. That’s a big thing for something so heavy and big.” The entire moving weight of the Mayall Telescope is 375 tons.

Rockosi said there was intensive pre-planning for the corrector’s early testing, and many of the tasks during this testing stage are focused on gathering data from evening observations. While DESI scientists have created automated controls to help position, focus and align all of the equipment, this testing run allows the team to fine-tune these automated tools.

“We’ll look at bright stars and test how well we can keep the telescope targeted in the same place and measure image quality,” Rockosi said. “We will test that we can repeatedly and reliably keep those lenses in the best possible alignment.”

The precision testing of the corrector is made possible by an instrument – now mounted atop the telescope – that was designed and built by Ohio State University researchers. This 1-ton device, which features five digital cameras and measuring tools supplied by Yale University, and electronics supplied by the University of Michigan, is known as the commissioning instrument.

This temporary instrument was built at the same weight and installed at the same spot where DESI’s focal plane will be installed once it is fully assembled. The focal plane will carry DESI’s robotic positioners. The commissioning instrument simulates how the telescope will perform when carrying the full complement of DESI components and is verifying the quality of DESI’s lenses.

“One of the biggest challenges with the commissioning instrument was aligning all five cameras with the corrector’s curved focal surface,” said Paul Martini, an astronomy professor at Ohio State University who led the R&D and installation of the commissioning instrument and is now overseeing its use. “Another was measuring their positions to a few millionths of a meter, which is far more precise than most astronomical instruments.” This positioning will ensure truer measurements of the lenses’ performance.

He said he is looking forward to the installation of DESI’s focal plane later this year. That will pave the way for DESI’s official “first light” of its robotic positioners and the start of its galaxy measurements.

“What got me excited about this field in the first place was going to telescopes and taking data, so it will be fun to have this next step,” he said.

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DESI is supported by the U.S. Department of Energy’s Office of Science; the U.S. National Science Foundation, Division of Astronomical Sciences under contract to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico; the Ministry of Economy of Spain; and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation. View the full list of DESI collaborating institutions, and learn more about DESI here: desi.lbl.gov.

Founded in 1931 on the belief that the biggest scientific challenges are best addressed by teams,Lawrence Berkeley National Laboratoryand its scientists have been recognized with 13 Nobel Prizes. Today, Berkeley Lab researchers develop sustainable energy and environmental solutions, create useful new materials, advance the frontiers of computing, and probe the mysteries of life, matter, and the universe. Scientists from around the world rely on the Lab’s facilities for their own discovery science. Berkeley Lab is a multiprogram national laboratory, managed by the University of California for the U.S. Department of Energy’s Office of Science.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

The National Optical Astronomy Observatory (NOAO)is the national center for ground-based nighttime astronomy in the United States and is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation Division of Astronomical Sciences.

The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.

The Heising-Simons Foundation is a family foundation based in Los Altos, California. The Foundation works with its many partners to advance sustainable solutions in climate and clean energy, enable groundbreaking research in science, enhance the education of our youngest learners, and support human rights for all people.

The Gordon and Betty Moore Foundation, established in 2000, seeks to advance environmental conservation, patient care and scientific research. The Foundation’s Science Program aims to make a significant impact on the development of provocative, transformative scientific research, and increase knowledge in emerging fields.

The Science and Technology Facilities Council (STFC) of the United Kingdom coordinates research on some of the most significant challenges facing society, such as future energy needs, monitoring and understanding climate change, and global security. It offers grants and support in particle physics, astronomy and nuclear physics; visit www.stfc.ac.uk.

Fermilab scientist Erik Ramberg and the Fermilab Archives present a new exhibit, “The Origins of Astronomy,” as part of their series on the history of physics in print. The exhibit can be viewed in the glass display case through the end of April in the Fermilab Art Gallery, which is open Monday through Friday, 8 a.m. to 4:30 p.m.

The exhibit showcases written publications, images, and works of art that reflect scientific and conceptual understandings of the night sky over four centuries, from a 1685 engraving of a celestial map by Alain Manesson Mallet to Karl Jansky’s 1932 findings on directional radio astronomy.

Science began as an explanation of what mankind saw in the heavens. The bright, immovable stars, stately motion of the planets, and the mysterious nature of the comets all seemed in significant contrast to the chaos of life on Earth. It took thousands of years to get to Copernicus, and hundreds more to get to our understanding of large-scale heavenly bodies.

Astronomers still strive to understand the structure and evolution of stars, galaxies and clusters of galaxies. See how we got to where we are by learning about some of astronomy’s most influential works.

This exhibit was designed by Erik Ramberg with assistance from Valerie Higgins and Karin Kemp.

It’s a moment that many at Fermilab have been waiting for: After a period of maintenance, construction, upgrades and repairs, every one of the laboratory’s nine particle accelerators is in run mode as of this publication. This means that all four of the accelerators in the lab’s main accelerator chain are running, as are both machines for the Muon g-2 experiment; both of the machines for the lab’s accelerator science program; and the lab’s applications-focused accelerator.

With the lab firing on all accelerator-cylinders, it’s a good time to provide a rundown of each member of Fermilab’s accelerator complex, from the oldies to the newest machine.

Since the lab’s inception in 1967, the family of particle accelerators that call Fermilab home has gone through many changes. Fermilab’s rich history of scientific discoveries began with the construction of the four-mile-circumference Main Ring in the early 1970s, followed by the installation of the game-changing Tevatron particle collider, which ran until 2011. Now the lab is in an era of neutrino and muon physics, and several of its accelerators and storage rings have been reconfigured to deliver new and more intense beams for numerous experiments.

Today, no fewer than nine main accelerators power technological advances and groundbreaking discoveries at Fermilab.

 

Linear accelerator (Linac)

• Shape: Linear
• Size: 140 meters
• Built: First operated in 1970, upgraded in 1992. New front end — a radio-frequency quadrupole — added in 2012. Major power upgrade in 2018.
• Energy boost: Up to 400 MeV (from original 200 MeV in the 1970s)
• Accelerated particles: Hydrogen ions
• Purpose: Creates initial acceleration of particles for Fermilab’s chain of particle accelerators; feeds Booster.

Booster

• Shape: Circular
• Size: 474 meters in circumference (1/7 that of the Main Injector; see below)
• Built: First reached full energy in 1971; upgrades for 15-hertz beam completed in 2018
• Energy boost: up to 8 GeV
• Accelerated particles: Protons
• Purpose: Strips electrons from hydrogen ions provided by the Linac, leaving protons. Gives further energy boost to proton beam to feed into Recycler. Provides protons for the production of muon beams for Muon g-2 and upcoming Mu2e. Also provides protons for production of low-energy neutrino beam for MicroBooNE, with two more detectors under construction: ICARUS and SBND (all part of the Short-Baseline Neutrino Program).

Recycler

• Shape: Circular
• Size: 3.3 kilometers in circumference
• Built: Completed in 1999
• Energy boost: N/A (stores protons at 8 GeV)
• Stored particles: Protons
• Purpose: Originally used for antiproton cooling and storage for Tevatron, converted to proton beam use in 2013. Combines bunches of protons in beam to increase intensity – a process known as “slip stacking.” Feeds Main Injector, located in same tunnel, below the Recycler. Also provides protons to produce muons (working with Muon Delivery Ring, below) for Muon g-2 and Mu2e experiments.

Main Injector

• Shape: Circular
• Size: 3.3 kilometers in circumference
• Built: Completed in 1999
• Energy boost: 8 GeV to 120 GeV
• Accelerated particles: Protons
• Purpose: Provides protons (at some of the world’s highest intensities) to create neutrino beams for NOvA and upcoming LBNF/DUNE. Sends protons to Fermilab Test Beam Facility. Until 2011, provided protons to antiproton ring and Tevatron.

Muon Delivery Ring

• Shape: Circular
• Size: 500 meters in circumference
• Built: Originally built in 1983 as Debuncher Ring for the Antiproton Source; renamed in 2012, modification completed in 2017
• Energy boost: N/A
• Stored particles: Protons, pions, muons
• Purpose: Provides beam for Muon g-2 and, in the future, Mu2e experiment. Proton beam from Recycler smashes into target to produce pions, which decay into muons for use in Muon g-2 experiment. For Mu2e experiment, will deliver protons.

Muon g-2 storage ring

• Shape: Circular
• Size: 50 meters in circumference
• Built: 1996 at Brookhaven National Laboratory; dismantled and shipped to Fermilab in 2013; full reassembly complete in 2017
• Energy boost: N/A (stores muons at 3.1 GeV)
• Stored particles: Muons
• Purpose: Store muons for the Muon g-2 experiment.

A2D2 compact accelerator

• Shape: Linear
• Size: Compact
• Built: 1996. Started up at Fermilab in 2017
• Energy boost: up to 9 MeV
• Accelerated particles: Electrons
• Purpose: Provides platform to investigate how electron beams can be used in industrial applications and better develop specific processes.

FAST electron injector

• Shape: Linear
• Size: 125 meters
• Built: 2012, upgraded in 2017
• Energy boost: up to 300 MeV (achieved November 2017)
• Accelerated particles: Electrons
• Purpose: Provides beam for IOTA accelerator at FAST facility, which will test new accelerator technologies.

IOTA storage ring

• Shape: Circular
• Size: 40 meters in circumference
• Built: 2018
• Energy boost: N/A (stores electrons at 100-150 MeV; in the future, will be capable of storing protons at 2.5 MeV)
• Accelerated particles: Will be able to store proton beams in the future
• Purpose: Stores electrons (and in the future, protons) to test new accelerator technologies.

On Feb. 24, 1987, light from a supernova that exploded 168,000 years ago in the Large Magellanic Cloud, a neighbor of the Milky Way, reached Earth. Astronomers Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile first reported the supernova, called SN 1987A (or simply 87A), which was one of the brightest in nearly four centuries.

A supernova such as 87A occurs when a star many times larger than our sun runs out of fuel in its core. At this point, the core is made of iron, and its fate hinges on the battle between two forces: Gravity tries to collapse it while electrons effectively repel each other, thanks to the Pauli exclusion principle, a quantum-mechanical effect. For a while, equilibrium is maintained, but the mass of the iron core keeps increasing, because of nuclear burning in the shell above it. Eventually, the core mass reaches a critical value called the Chandrasekhar limit, and the relentless pull of gravity wins. The core collapses on itself in near free fall, and a shockwave forms around it. Heated by the energy of escaping neutrinos, the shockwave ejects the outer layers of the star in a catastrophic blast that can briefly shine more brightly than entire galaxies. After losing its energy to neutrino emission, the core finally settles into what is known as a neutron star, effectively a giant nucleus made primarily of neutrons.

By the time Duhalde and Shelton saw light from 87A, three neutrino detectors around the world had already picked up evidence of the supernova. Most of the energy released in a supernova is emitted as neutrinos, nearly massless subatomic particles that react rarely with ordinary matter. Because they are so weakly interacting, neutrinos can slip out of the envelope of a collapsing supernova hours before particles of light, which ride the explosion’s shockwave, are ejected.

Neutrinos produced by 87A arrived on Earth just before the light from the explosion did. Irvine-Michigan-Brookhaven (IMB), a neutrino observatory in Ohio on the shore of Lake Erie, detected eight neutrino events. Baksan Neutrino Observatory in Russia detected five more, and Kamiokande II, a neutrino detector deep underground in a Japanese mine, saw 11. It was the first time that neutrinos from a supernova had been detected – although the neutrino scientists didn’t realize it until after Duhalde and Shelton announced their observation. They found the neutrino events in their data only when they looked for them upon hearing the news about the supernova.

Something incredible waiting to be known?

More than 30 years later, scientists are building the international Deep Underground Neutrino Experiment (DUNE), hosted by Fermilab. Its 70,000-ton liquid-argon detector will be located almost a mile underground at Sanford Underground Research Facility in South Dakota, waiting for another burst of supernova neutrinos to arrive. The discovery would portend a new exploding star somewhere in the Milky Way.

Kate Scholberg, a particle physicist at Duke University, says supernova neutrinos could teach us a lot about supernovae and particle physics if we detect them the next time an event like 87A occurs. That’s because the neutrinos carry information about the supernova with them as they travel across space. The signals the neutrinos make in particle detectors like DUNE would allow physicists to draw conclusions about the conditions in which the neutrinos were made and provide evidence for the fate of the exploding star.

“You can actually see the processes that are happening in real time as the neutron star is being born,” said Scholberg, who studies neutrinos as part of DUNE.

These processes could point to new physics. For example, if exotic particles are produced in a supernova, traces of their existence would be apparent in the signal made by the neutrinos. That’s because physicists can calculate the total energy produced by a supernova, and they can estimate how much of it was emitted as neutrinos from the measurement. If the total energy detected doesn’t add up to the total expected, it could hint at new particles being produced.

“The detection of a supernova in 1987 from Kamiokande was, to me, one of the most impressive detections for particle physics,” said Inés Gil Botella, a scientist at Spain’s Center for Energy, Environment and Technology, or CIEMAT, and one of the leads on DUNE’s supernova search. “It opened a way to understanding the universe through particles other than photons. This new multimessenger era of astrophysics really started with the detection of supernova neutrinos.”

The DUNE dimension

While detectors captured only 24 of the neutrinos emitted from 87A, hundreds of peer-reviewed papers were published as a result of the discovery and subsequent research. When DUNE is completed, it could see far more neutrinos and contribute to a similar – and entirely novel – flurry of research.

“DUNE has several capabilities that are truly unique among all large neutrino detectors when it comes to studies of supernova neutrinos,” said Steven Gardiner, a Fermilab scientist who works on simulating what occurs when a supernova neutrino enters a detector.

DUNE is different from Cherenkov detectors such as Kamiokande in several ways, including that it uses liquid argon instead of water as the target medium. Liquid-argon detectors spot neutrinos when they collide with argon nuclei. Argon’s nucleus is composed of protons and neutrons that are arranged in various energy states. When a neutrino collides with an argon nucleus, a proton or neutron in a lower energy state can be elevated to a higher energy state and lead to the emission of particles from the argon nucleus via its de-excitation. Some of these particles can be observed by the detector.

“When the nucleus de-excites, a few different things can happen,” Gardiner said. “The nucleus can emit gamma rays, neutrons, protons or heavier nuclear fragments. You can potentially see gamma rays in liquid argon, because they’ll scatter electrons in the argon, and you’ll see little blips that come from them.”

Cherenkov detectors, which look primarily for electron antineutrinos striking bare protons, can’t reconstruct gamma rays with as much detail as liquid-argon detectors can.

Because of the complicated nature of the energy reconstruction, it’s quite a challenge to reconstruct supernova neutrino events in a liquid-argon detector. Gardiner is currently building computer simulations that can model the various signatures that can occur when a neutrino interacts with the liquid argon in DUNE.

“The difficulty is, because you have so many argon excited states available, you have all sorts of different signatures that could be produced in your detector,” he said. “And you have to deal with that level of complexity to fully reconstruct the energy from a neutrino collision.”

Then there’s the challenge of teasing out the signal from the noise. Supernova neutrinos carry far less energy than, say, neutrinos produced by a particle accelerator, so the signals they produce in the argon are weaker. Unearthing these low-energy interactions requires both a sensitive detector and a knowledge of the interaction’s various signatures.

“High-energy neutrinos are easier to detect, and their interactions are well-known. We know how they behave,” Gil Botella said. “But at these low, supernova-neutrino energies, the interactions with argon are not very well-known. We don’t have much experimental data to say what happens when a low-energy neutrino interacts with argon.”

And scientists at the world’s other neutrino projects are looking to change that, planning experiments that would paint a clearer picture of low-energy neutrinos.

“Studying neutrinos is a tricky business, and we have more work to do, but DUNE’s technological capabilities make those challenges far more tractable,” Gardiner said. “The physics payoffs will be huge. If we’re going to tackle these questions, DUNE is a good way to do it.”

Oscillation station

DUNE could also help inform our understanding of neutrino oscillation in a way that other detectors cannot. In Cherenkov detectors, the signal is produced mostly by electron antineutrinos interacting with water molecules. Conversely, liquid argon also samples electron neutrinos from the supernova’s ejecta.

“We need both electron neutrinos and antineutrinos to disentangle oscillation scenarios,” said Alex Friedland, a particle physicist and senior staff scientist at SLAC National Accelerator Laboratory in California. DUNE, because it will be the only detector that can see electron neutrinos, adds a missing piece to that puzzle.

Neutrinos oscillate between three flavors (electron, muon or tau) as they move through space. Physicists have studied neutrino oscillations in neutrinos produced in the sun, in ­­Earth’s atmosphere, from nuclear reactors and in high-energy particle beams created by particle accelerators. But they haven’t been able to study them in supernovae, where the number of neutrinos produced is simply off the charts compared to other sources.

“This is the ultimate intensity frontier,” Friedland said. “Nature does it for us, so we just have to take advantage of that. The supernova is a laboratory on the other side of the galaxy. It carries out experiments, and we ‘just’ have to build the detector and make a measurement. Of course, it’s useful to keep in mind that this measurement ‘just’ happens to be one of the most challenging tasks that DUNE, the most advanced neutrino detector ever built, will undertake.”

Neutrino oscillation typically describes a single particle changing flavors, but under the right circumstances — such as in a collapsing supernova — many neutrinos can oscillate collectively.

“Collective oscillation means that you have neutrinos that go through the background of other neutrinos, and a flavor state of a given neutrino knows about what all the other neutrinos that it passes are doing in terms of flavor,” Friedland said.

With enough neutrino signals – which a detector such as the giant DUNE could amass – physicists can reconstruct the energy spectrum of the electron neutrinos arriving at Earth. This spectrum can have striking features imprinted on it by collective oscillations of neutrinos inside the supernova. With that information, they can see how the neutrinos evolved collectively in the dying star.

The information can give them clues about what happened to the star itself, as well. The neutrino density is so high in a core-collapse supernova like 87A that it affects how the star explodes. The shockwave of the explosion is propelled by what physicists call the neutrino-driven wind.

Other core-collapse events might not produce a supernova that we can see easily from Earth, but we’ll know they occurred when the neutrino detectors register a burst.

“When a star collapses into a black hole, you likely don’t get any fireworks,” Scholberg explained. “The observers might see nothing, or just see a star wink out. Those kinds of events would be seen brightly in neutrinos.”

Once the DUNE detectors are in place, they’ll be used to take measurements of neutrinos coming from Fermilab accelerators and wait patiently for a supernova to explode. This happens in our galaxy on average once every 30 to 50 years.

“That’s the drawback of the supernova neutrino world; we’re always waiting,” Scholberg said.  “You better not miss anything.”

When it does occur, a core-collapse supernova will be a major event that will affect multiple fields of research, including particle physics and astrophysics.

“It’s so impressive: Supernovae produce a huge number of neutrinos, they travel such a long distance, and you get a signal directly from something that’s kiloparsecs away,” Gil Botella said. “It’s really amazing to get access to information inside a star like that. It’s the connection with the objects in the universe — the unknown of the universe.”

Members of the public can sign up to receive alerts from the SuperNova Early Warning System (SNEWS). The automated system currently includes seven neutrino experiments in Canada, China, Italy, Japan and at the South Pole. When neutrinos produced in a supernova reach Earth, SNEWS will send out email alerts to announce their arrival, which would captivate the research community.

“Once the supernova happens, you can forget about everything else that we were thinking about,” Friedland said. “The world of science will be talking about that for at least a year or more.”

The Deep Underground Neutrino Experiment is supported in part by the U.S. Department of Energy Office of Science.