From The Sanford Underground Research Facility-SURF (US): “The neutrino puzzle”

SURF-Sanford Underground Research Facility, Lead, South Dakota, USA.

From The Sanford Underground Research Facility-SURF (US)

Homestake Mining, Lead, South Dakota, USA.
Homestake Mining Company

August 30, 2021 [Found in a year-end round up.]
Constance Walter

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Vincent Guiseppe in a clean suit in the Majorana Demonstrator cleanroom on the 4850 Level of SURF. Behind him, the Majorana Demonstrator shielding is opened to reveal the copper core and cryostat module, which houses the inner detector components. Photo by Nick Hubbard.

Imagine trying to put together a jigsaw puzzle that has no picture for reference, is missing several pieces and, of the pieces you do have, some don’t quite fit together.

Welcome to the life of a neutrino researcher.

Vincente Guiseppe began his neutrino journey 15 years ago as a post-doc at DOE’s Los Alamos National Laboratory (US). He worked with germanium detectors and studied radon while a graduate student and followed the scientific community’s progress as the Solar Neutrino Problem was solved. The so-called Solar Neutrino Problem was created when Dr. Ray Davis Jr., who operated a solar neutrino experiment on the 4850 Level of the Homestake Gold Mine, discovered only one-third of the neutrinos that had been theorized. Nearly 30 years after Davis began his search, the problem was solved with the discovery of neutrino oscillation.

“I began to understand that neutrinos had much more in store for us. That led me to move to neutrino physics and set me up to transition to The Majorana Demonstrator (Majorana) project,” said Guiseppe, who is now a co-spokesperson for Majorana, located nearly a mile underground at SURF, and a senior research staff member at DOE’s Oak Ridge National Laboratory (US).

Majorana uses germanium crystals in a search for the theorized Majorana particle—a neutrino that is believed to be its own antiparticle. Its discovery could help unravel mysteries about the origins of the universe and would add yet another piece to this baffling neutrino puzzle.

We caught up with Guiseppe recently to talk about neutrinos—what scientists know (and don’t know), why neutrinos behave so strangely and why scientists keep searching for this ghost-like particle.

SURF: What are neutrinos?

Guiseppe: Let’s start with what we know. Of all the known fundamental particles that have mass, neutrinos are the most abundant—only the massless photon, which we see as light, is more abundant. We know their mass is quite small, but not zero—much lighter than their counterparts in the Standard Model of Physics—and we know there are three types and that they can change flavors. They also rarely interact with matter, which makes them difficult to study.

Standard Model of Particle Physics, Quantum Diaries.

All of these data points are pieces of that neutrino puzzle. But every piece is important if we want to complete the picture.

SURF: Why should we care about the neutrino?

Guiseppe: We care because they are so abundant. It’s almost embarrassing to have something that is so prevalent all around us and to not fully understand it. Think of it this way: You see a forest and the most abundant thing in that forest is a tree. But that’s all you know. You don’t know anything about how a tree operates. You don’t know how it grows, you don’t know why it’s green, you don’t know why it’s alive. It would be embarrassing to not know that. But that’s not the case with trees. Something so abundant as what we see in nature—animal species, trees, plants—we understand them completely, there’s nothing surprising. So, the fact that they are so abundant, and yet we know so little about them, brings a sort of duty to understand them.

SURF: What intrigues you most about neutrino research?

Guiseppe: Most? I would say the breadth of research and the big questions that can be answered by a single particle. While similar claims could be made about other particle research, the experimental approach is wide open. We look for neutrinos from nuclear reactors, particle accelerators, the earth, our atmosphere, the sun, from supernovae, and some experiments are only satisfied if we find no neutrinos, as in the case of neutrinoless double-beta decay searches. Neutrino research places detectors in underground caverns; at the South Pole; in the ocean; and even in a van for drive-by neutrino monitoring for nuclear safeguard applications. It’s a diverse field with big and unique questions.

SURF: What is oscillation?

Guiseppe: Oscillation is the idea that neutrinos can co-exist in a mixture of types or “flavors.” While they must start out as a particular flavor upon formation, they can evolve into a mixture of other flavors while traveling before falling into one flavor upon interaction with matter or detection. Hence, they are observed to oscillate between flavors from formation to detection.

SURF: It’s a fundamental idea that a thing can’t become another thing unless acted upon by an outside force or material. How can something spontaneously become something it wasn’t a split second ago? And why are we OK with that?

Guiseppe: Are people really okay with the idea of neutrinos changing flavors? I think we are, inasmuch as we are really okay with the implications of quantum mechanics? (As an aside, this reminds me of a question I asked my undergraduate quantum mechanics professor. I felt I was doing fine in the class and could work the problems but was worried that I really didn’t understand quantum mechanics. He responded with a slight grin: “Oh, no one really ‘understands’ quantum mechanics.”).

It is quantum mechanics at work that makes this flavor change possible. Since neutrinos come in three separate flavors and three separate masses (and more importantly, each flavor does not come as a definite mass), they can exist in a quantum mechanical mixture of flavors. The root of your concern stems from the idea of its identify—what does it mean to change this identity?

The comforting aspect is that neutrinos are not found to change speed, direction, mass, shape, or anything else that would require an outside force or energy in the usual sense. By changing flavor, the neutrino is only changing its personality and the rules by which it should follow at a given time.

While this bit of personification is probably not comforting, it is only how the neutrino must interact with other particles that changes over time. You could think of the neutrino as being formed as one type, but then realizing it is not forced into that identity. It then remains in an indecisive state while being swayed to one type over another before finally making a decision upon detection or other interaction. In that sense, it is not a spontaneous change, but the result of a well thought-out (or predictable) decision process.

SURF: What is a Majorana Particle and why is it important?

Guiseppe: A Majorana particle is one that is indistinguishable from its antimatter partner. This sets it apart from all other particles. With the Majorana Demonstrator, we are looking for this particle in a process called neutrinoless double-beta decay.

Neutrinoless double-beta decay is a nuclear process whereby two neutrons transform into two protons and electrons (aka, beta particles), but without the emission of two anti-neutrinos. This is in contrast to the two neutrino double-beta decay process where the two anti-neutrinos are emitted; a process that has been observed.

SURF: Why neutrinoless double-beta decay?

Guiseppe: Neutrinoless double-beta decay experiments offer the right mix of simplicity, experimental challenges, and the potential for a fascinating discovery. The signature for neutrinoless double-beta decay is simple: a measurement made at a specific energy and at a fixed point in the detector. But it’s a rare occurrence that is easily obscured so reducing all background (interferences) that can partially mimic this signature and foil the measurement is critical. Searching for this decay requires innovative detectors, as well as the ability to control the ubiquitous radiation found in everything around us.

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The Majorana Demonstrator’s cryostat module inside the detector shielding. Photo by Nick Hubbard.

SURF: After so many years, how do you stay enthusiastic about neutrino research?

Guiseppe: Its book isn’t finished yet. We have more to learn and more questions to answer—we only need the means to do so. I stay enthused due to the likelihood of some new surprises (or comforting discoveries) that await. Along the way, we can continue to make advances in detector technology and develop new (or cleaner) materials, which inevitably lead to applications outside of physics research. In the end, chasing down neutrino properties and the secrets they may hold remains exciting due to clever ideas that keep the next discovery within reach.

See the full article here .


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About us: The Sanford Underground Research Facility-SURF (US) 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.

The LBNL LZ Dark Matter Experiment (US) Dark Matter project at SURF, Lead, SD, USA.

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 U Washington MAJORANA Neutrinoless Double-beta Decay Experiment Demonstrator experiment (US), 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.

The LUX Xenon dark matter detector | Sanford Underground Research Facility 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 National Accelerator Laboratory(US) 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 DUNE LBNF (US) from FNAL to SURF >, Lead, South Dakota, USA

FNAL DUNE LBNF (US) Caverns at Sanford Lab.

U Washington MAJORANA Neutrinoless Double-beta Decay Experiment (US) 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 Germanium Detector Array (or GERDA) experiment is searching for neutrinoless double beta decay (0νββ) in Ge-76 at the underground Laboratori Nazionali del Gran Sasso (LNGS) for a future tonne-scale 76Ge 0νββ search.

Compact Accelerator System for Performing Astrophysical Research (CASPAR). Credit: Nick Hubbard.

Compact Accelerator System for Performing Astrophysical Research (CASPAR). Credit: Nick Hubbard.
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.”