From Sanford Underground Research Facility: ‘Why DUNE? [Part III] Shedding light on the unification of nature’s forces”

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From Sanford Underground Research Facility

Homestake Mining Company

May 22, 2020
Erin Broberg

Part III in our series exploring the science goals of the international Deep Underground Neutrino Experiment [image below].

The Deep Underground Neutrino Experiment (DUNE) could help us learn more about physics beyond the Standard Model. Courtesy Fermilab

Master theoretical physicists laid the foundations of the Standard Model throughout the second half of the twentieth century. With outstanding success, it explained how particles like protons, neutrons and electrons interact on a subatomic level. It also made Nobel Prize-winning predictions about new particles, such as the Higgs Boson, that were later observed in experiments. For decades, the Standard Model has been the scaffolding on which physicists drape quantum concepts from magnetism to nuclear fusion.

Despite its remarkable dexterity and longevity, however, some physicists have described the Standard Model as “incomplete,” “ugly” and, in some instances, even “grotesque.”

“The Standard Model is an effective theory, but we are not satisfied,” said Chang Kee Jung, a professor of physics at Stony Brook University. “Physicists, in some sense, are perfectionists. We always want to know exactly why things work a certain way.” While the Standard Model is incredibly useful, it is far from perfect.

A portion of the Lagrangian standard model transcribed by T.D. Gutierrez. Courtesy Symmetry Magazine.

Standard Model of Particle Physics, Quantum Diaries

In a bewildering example, the Standard Model predicted that neutrinos, the universe’s most abundant particle, would be massless. In 1998, the Super-Kamiokande experiment in Japan caught the Standard Model in a lie.

Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

Neutrinos do indeed have mass, albeit very little. Further complicating matters, the Standard Model doesn’t explain dark matter or dark energy; combined, these account for 95 percent of the universe. In other cases, the Standard Model requires physicists to begrudgingly plug in arbitrary parameters to reflect experimental data.

Unwilling to ignore these flaws, physicists are looking for a new, more perfect model of the subatomic universe. And many are hoping that the Deep Underground Neutrino Experiment, hosted by the Department of Energy’s Fermi National Accelerator Laboratory, can put their theories to the test.

Grander theories of the quantum world

Leading alternatives to the Standard Model attempt to unify the three quantum forces: strong, weak and electromagnetic. Physicists have demonstrated that, at extremely high energies, the weak and electromagnetic force become indistinguishable. Many believe that the strong force can be unified in the same way.

“Grand unification is the beautiful idea that there was a single force at the beginning of the universe, and what we see now is three manifestations of that original force,” said Jonathan Lee Feng, particle and cosmology theorist at the University of California, Irvine. This class of “Grand Unified Theories” is charmingly abbreviated as “GUTs.”

In their search for a GUT, theorists have been a bit too successful. They haven’t created just one alternative to the Standard Model—they’ve created hundreds. These models unify quantum forces, explain the mass of a neutrino and eliminate many arbitrary parameters. Some are practical and bare-boned, others far-fetched and elaborate, but nearly all are mathematically solid.

Even so, they can’t all be “right.”

“You can write a logically and mathematically consistent theory, but that doesn’t mean it matches the real mechanisms of the universe,” Jung said. “Nature chooses its own way.”

Testing physics beyond the Standard Model

GUTs are a major branch of theory. But others also attempt to reshape our understanding of the universe. Surrounded by more models than could possibly be correct, theorists around the world are asking the universe for a nudge in the right direction.

Just as the Standard Model predicted novel particles in the twentieth century that were later discovered through experimentation, new theories also predict never-before-seen phenomena. Some models predict the decay of a particle once thought immortal. Others hint at a fourth generation of neutrino. Still others foretell of particles that communicate between our realm and the realm of dark matter.

“We can continue to speculate and refine these models, but if we actually witnessed one of these predictions, we’d have much more precise hints about where to go,” Feng said.

Enter DUNE. The main goal of the international Deep Underground Neutrino Experiment is to keep a watchful eye on a beam of neutrinos traveling from Fermilab to detectors deep under the earth at Sanford Underground Research Facility. However, the experiment is also designed to be sensitive to a slew of interactions predicted by avant-garde theories. The observation of even one of these predictions would rule out dozens of theories and guide the next generation of quantum theory.

Tuned to witness quantum strangeness

Proton decay

The Standard Model dictates that protons—basic building blocks of matter best known for how they clump with neutrons in the center of an atom—are stable particles, destined to live forever.

However, many Grand Unified Theories have predicted that, eventually, protons will decay. While different models disagree on the specific mechanisms that cause this decay, the general consensus is that proton decay is a good place to start investigating physics beyond the Standard Model.

To validate these theories, physicists just have to glimpse the death of a proton.

In the early 1950s, Maurice Goldhaber, an esteemed physicist who later directed Brookhaven National Laboratory, postulated that protons live at least 10^16 years. If their lifespan were any shorter, the radiation from frequent decays would destroy the human body. Thus, Goldhaber said, you could “feel it in your bones” that the proton was long-lived. Over time, experiments determined that protons lifetime was even longer—at least 10^34 years.

According to current estimates, you would have to watch one proton for a minimum of 100,000,000,000,000,000,000,000,000,000,000,000 years—without blinking—in order to see it decay. Sensible physicists aren’t quite that patient.

By watching a multitude of protons at once, researchers can greatly increase their chances of seeing a decay within their own lifetime (and still be alive to receive the Nobel Prize for their discovery). DUNE detectors will monitor 40,000 tons of liquid argon.

FNAL DUNE Argon tank at SURF

Each atom of argon contains 18 protons. If one out of this incredible number of protons decays during DUNE’s lifetime, it will show up in DUNE’s data.

“If a proton decay is discovered, it is a revolutionary discovery—a once-in-a-generation discovery,” said Jung, who has played various leadership roles in DUNE.

An invisible neutrino

Neutrinos are subatomic particles; waiflike, abundant and neutral, they hardly interact with normal matter at all. DUNE is designed to monitor how neutrinos oscillate, or change between three different types of neutrino, as they stream through the Earth. But DUNE could also see something extra hidden in its data.

“In the Standard Model, there are three types of neutrino: the electron neutrino, the muon neutrino and the tau neutrino. But why is there not a fourth generation? Why not five? What stops it at three? That is not known,” Jung said.

There are subatomic hints of another type of neutrino, called a sterile neutrino, that interacts even less than the other known types. If it exists, the only way it could be measured is the way in which it joins the oscillation pattern of neutrinos, disrupting the pattern physicists expect to see.

There are subatomic hints of another type of neutrino, called a sterile neutrino, that interacts even less than the other known types. Courtesy Fermilab.

“If what we see doesn’t match our three-flavor oscillation pattern, it will tell us a lot about what is incomplete about our understanding of the universe,” said Elizabeth Worcester, DUNE physics co-coordinator and physicist at Brookhaven National Laboratory. “It could point to the existence of sterile neutrinos, a new interaction or even some other crazy thing we haven’t thought of yet. It would take some untangling to understand what the data is really telling us.”

Investigating dark matter

Dark matter is a mysterious, invisible source of matter responsible for holding vast galaxies together. Although not directly tied to theories of unification, the long-standing mystery of dark matter transcends the Standard Model. And depending on its true characteristics, DUNE could be the first to detect it.

“Dark matter is an enormous question in our field,” said Feng, who has worked on a specific dark matter theory, called WIMP theory, for 22 years. “There is a lot of interesting creative work being done in theory, but hints from experiments like DUNE would be really helpful.”

According to WIMP theory, dark matter is composed of weakly interacting, massive particles (WIMPs). If these particles exist, some of them are expected to pass through the Sun. There, they would interact with other particles, losing energy and sinking into the Sun’s core. Over time, enough WIMPs would gravitate toward the Sun’s core that they would annihilate with each other and release high-energy neutrinos in all directions. As you might guess, DUNE would be ready to detect these neutrinos. Researchers could reconstruct their trajectory, tracing them back to the Sun and, indirectly, to the WIMPs that produced them.
Dark Matter Background
Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

Fritz Zwicky from http://

Coma cluster via NASA/ESA Hubble

In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.

Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.

Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970.

The Vera C. Rubin Observatory currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova


While Feng hasn’t given up on WIMPs, he has recently started working on another dark matter theory that involves light dark matter particles. This theory predicts that, in addition to looking for dark matter directly, we could also learn more about dark matter through so-called “mediator particles.”

“If you imagine we could talk to dark matter on the phone, mediator particles would be the wire that connects us to it,” Feng said. If this theory is accurate, mediator particles could potentially be created as by-products in Fermilab’s particle accelerator and show themselves in one of DUNE’s detectors.

Whatever its true characteristics, dark matter might reveal itself in DUNE, offering clues to yet another universe-sized mystery.

Looking where the light is

“There are other interactions beyond the Standard Model that DUNE could be sensitive to,” Worcester said. “Spontaneous neutron-antineutron oscillation, nonstandard interactions, exotic things like Lorentz violation, which would mean that almost all theory is broken.” The list goes on. “If it feels like a grab bag, that’s because it is.”

Worcester likens DUNE’s multifaceted approach to the streetlamp effect. If you drop your keys on a dark street, you look under the streetlamp to find them. They may not be within the beam of light created by the streetlamp, but you have no hope of finding the keys in the darkness. So, you look where the light is.

When researchers are attempting to look beyond what is known, advanced experiments like DUNE become their streetlamps, casting puddles of light onto unfamiliar physics.

“It could be that some answers are still in the dark, but if we keep creating sophisticated experiments, we’ll find them,” Worcester said.

So, why DUNE? Amidst its search for the origin of matter and supernovas on the galactic horizon, DUNE will also shine a bright light on physics beyond the Standard Model.

See the full article here .

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About us.
The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.

LBNL LZ project at SURF, Lead, SD, USA, will replace LUX at SURF

In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
“LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

FNAL LBNE/DUNE from FNAL to SURF, Lead, South Dakota, USA


U Washington Majorana Demonstrator Experiment at SURF

The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.


CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”