Underground neutrino experiment sets the stage for deep discovery about matter

Underground neutrino experiment sets the stage for deep discovery about matter
Credit: Sanford Underground Research Facility; photographer Matthew Kapust

If equal amounts of matter and antimatter had formed in the Big Bang more than 13 billion years ago, one would have annihilated the other upon meeting, and today's universe would be full of energy but no matter to form stars, planets and life. Yet matter exists now. That fact suggests something is wrong with Standard Model equations describing symmetry between subatomic particles and their antiparticles. In a study published in Physical Review Letters, collaborators of the MAJORANA DEMONSTRATOR, an experiment led by the Department of Energy's Oak Ridge National Laboratory, have shown they can shield a sensitive, scalable 44-kilogram germanium detector array from background radioactivity.

This accomplishment is critical to developing and proposing a much larger future experiment—with approximately a ton of detectors—to study the nature of neutrinos. These electrically neutral particles interact only weakly with matter, making their detection exceedingly difficult.

"The excess of matter over antimatter is one of the most compelling mysteries in science," said John Wilkerson of ORNL and the University of North Carolina, Chapel Hill. Wilkerson leads the MAJORANA DEMONSTRATOR, which involves 129 researchers from 27 institutions and 6 nations. "Our experiment seeks to observe a phenomenon called 'neutrinoless ' in atomic nuclei. The observation would demonstrate that neutrinos are their own antiparticles and have profound implications for our understanding of the universe. In addition, these measurements could provide a better understanding of neutrino mass."

In a 2015 report of the U.S. Nuclear Science Advisory Committee to the Department of Energy and the National Science Foundation, a U.S.-led ton-scale experiment to detect neutrinoless double-beta decay was deemed a top priority of the nuclear physics community. Nearly a dozen experiments have sought neutrinoless double-beta decay, and as many future experiments have been proposed. One of their keys to success depends on avoiding background that could mimic the signal of neutrinoless double-beta decay.

That was the key accomplishment of the MAJORANA DEMONSTRATOR. Its implementation was completed in South Dakota in September 2016, nearly a mile underground at the Sanford Underground Research Facility. Siting the experiment under nearly a mile of rock was the first of many steps collaborators took to reduce interference from background. Other steps included a cryostat made of the world's purest copper and a complex six-layer shield to eliminate interference from cosmic rays, radon, dust, fingerprints and naturally occurring radioactive isotopes.

"If you're going to search for neutrinoless double-beta decay, it's critical to know that radioactive background is not going to overwhelm the signal you seek," said ORNL's David Radford, a lead scientist in the experiment.

There are many ways for an atomic nucleus to fall apart. A common decay mode happens when a neutron inside the nucleus emits an electron (called a "beta") and an antineutrino to become a proton. In two-neutrino double-beta decay, two neutrons decay simultaneously to produce two protons, two electrons and two antineutrinos. This process has been observed. The MAJORANA Collaboration seeks evidence for a similar decay process that has never been observed, in which no neutrinos are emitted.

Conservation of the number of leptons—subatomic particles such as electrons, muons or neutrinos that do not take part in strong interactions—was written into the Standard Model of Physics. "There is no really good reason for this, just the observation that it appears that's the case," said Radford. "But if lepton number is not conserved, when added to processes that we think happened during the very early universe, that could help explain why there is more matter than antimatter."

Underground neutrino experiment sets the stage for deep discovery about matter
Credit: Sanford Underground Research Facility; photographer Matthew Kapust

Many theorists believe that the lepton number is not conserved, that the neutrino and the antineutrino—which were assumed to have opposite lepton numbers—are really the same particle spinning in different ways. Italian physicist Ettore Majorana introduced that concept in 1937, predicting the existence of particles that are their own antiparticles.

The MAJORANA DEMONSTRATOR uses germanium crystals as both the source of double-beta decay and the means to detect it. Germanium-76 (Ge-76) decays to become selenium-76, which has a smaller mass. When germanium decays, mass gets converted to energy that is carried away by the electrons and the antineutrinos. "If all that energy goes to the electrons, then none is left for neutrinos," Radford said. "That's a clear identifier that we found the event we're looking for."

The scientists distinguish two-neutrino versus neutrinoless decay modes by their energy signatures. "It's a common misconception that our experiments detect neutrinos," said Jason Detwiler of the University of Washington, who is a co-spokesperson for the MAJORANA Collaboration. "It's almost comical to say it, but we are searching for the absence of neutrinos. In the neutrinoless decay, the released energy is always a particular value. In the two-neutrino version, the released energy varies but is always smaller than for neutrinoless double-beta decay."

The MAJORANA DEMONSTRATOR has shown that the neutrinoless double-beta decay half-life of Ge-76 is at least 1025 years—15 orders of magnitude longer than the age of the universe. So it's impossible to wait for a single germanium nucleus to decay. "We get around the impossibility of watching one nucleus for a long time by instead watching on the order of 1026 nuclei for a shorter amount of time," explained co-spokesperson Vincente Guiseppe of the University of South Carolina.

Chances of spotting a neutrinoless double-beta decay in Ge-76 are rare—no more than 1 for every 100,000 two-neutrino double-beta decays, Guiseppe said. Using detectors containing large amounts of germanium atoms increases the probability of spotting the rare decays. Between June 2015 and March 2017, the scientists observed no events with the energy profile of neutrinoless decay, the process that has not yet been observed (this was expected given the small number of germanium nuclei in the detector). However, they were encouraged to see many events with the energy profile of two-neutrino decays, verifying the detector could spot the decay process that has been observed.

The MAJORANA Collaboration's results coincide with new results from a competing experiment in Italy called GERDA (for GERmanium Detector Array), which takes a complementary approach to studying the same phenomenon. "The MAJORANA DEMONSTRATOR and GERDA together have the lowest background of any neutrinoless double-beta decay experiment," said Radford.

The DEMONSTRATOR was designed to lay the groundwork for a ton-scale experiment by demonstrating that backgrounds can be low enough to justify building a larger detector. Just as bigger telescopes collect more light and enable viewing of fainter objects, increasing the mass of germanium allows for a greater probability of observing the rare decay. With 30 times more germanium than the current experiment, the planned one-ton experiment would be able to spot the of just one germanium nucleus per year.

The MAJORANA DEMONSTRATOR is planned to continue to take data for two or three years. Meanwhile, a merger with GERDA is in the works to develop a possible one-ton detector called LEGEND, planned to be built in stages at an as-yet-to-be-determined site.

LEGEND 200, the LEGEND demonstrator and step towards a possible future ton-scale experiment, will be a combination of GERDA, MAJORANA and new detectors. Scientists hope to start on the first stage of LEGEND 200 by 2021. A ton-scale experiment, LEGEND 1000, would be the next stage, if approved. "This merger leverages public investments in the MAJORANA DEMONSTRATOR and GERDA by combining the best technologies of each," said LEGEND Collaboration co-spokesperson (and long-time MAJORANA spokesperson up until last year) Steve Elliott of Los Alamos National Laboratory.

The title of the Physical Review Letters paper is "Search for Neutrinoless Double Beta Decay in 76Ge with the MAJORANA DEMONSTRATOR."

Explore further

CUORE experiment constrains neutrino properties

More information: C. E. Aalseth et al, Search for Neutrinoless Double- β Decay in Ge76 with the Majorana Demonstrator, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.120.132502
Journal information: Physical Review Letters

Citation: Underground neutrino experiment sets the stage for deep discovery about matter (2018, March 26) retrieved 20 September 2019 from https://phys.org/news/2018-03-underground-neutrino-stage-deep-discovery.html
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User comments

Mar 26, 2018
My guess, and it's purely a guess, is that Dark Matter has something to do with the imbalance of matter and antimatter.

Mar 26, 2018
So, when it becomes obvious that the cosmogony model does not correspond with the actual universe, who is wrong. the universe or the model??

Scientists in modern times have consistently decided that there is something wrong with the universe and retain the faulty model at all costs. Very sad for science...that is what religious models did for thousands of years and was rejected by 'Natural Philosophy', as it was then called, which decided to build up its philosophy based on empirical observation alone and not to contrive a model and then assume hidden or unobservable mechanisms in nature to support the model as the religionists and other philosophers did.

Mar 26, 2018
The Standard Model is called "standard" because it predicts everything we've ever seen in particle physics. There are no experiments we've ever done that it does not correctly predict the outcomes of. This is actually unfortunate; it's so successful we've been having a really bad time for the last fifty or sixty years coming up with any new physics (the Higgs was the last prediction and that was in the 1960s). We've found a few new wrinkles since then-- pentaquarks are a prediction that has not yet been verified conclusively-- but right now the neutrino sector looks to a lot of people like the most likely source of new physics beyond the SM.

As far as this being evidence, unfortunately none of the experiments in this article has been done. We're just barely testing the water right now with neutrino mass oscillations, and don't have enough data to claim physicists aren't discarding models when they don't fit the evidence like you're doing here, @RKS.

Mar 27, 2018
If science does not know what matter is and how and from what it forms, how can it make conclusions, how matter disappears and how it decays? As long as science does not identify what matter forms, no one will ever find out the true causes of many phenomena. Science caught on the existence of dark matter, as a drunken man caught the fence to not fall. If science does not understand what matter is, how can it discuss the existence of antimatter? This invention of the Higgs boson is an illusion and a fatamorgana, because science does not understand how and from what particle was created, and is not stable and natural. Who produced such a "stillborn"? This was unconsciously produced by particle accelerator specialists, thinking that these pipes were in complete vacuum.

Mar 27, 2018
ERROR AND LOSS OF THE EVENT OF THE ASTHER SUBSTANCE, FILLED BY THE FUNCTIONAL UNIVERSE, AND THESE PIPES. Aether can be "irritated" with increased magnetism and increased rate of movement of the particle, but what gets, disappears and is not stable !!

Mar 27, 2018
@milnik, what exactly do you mean by "what matter is?" All the matter we've ever seen is made up of particles, specifically fermions. They have the characteristics that make matter: they can't exist in the same location, making matter take up space (due to the Pauli exclusion principle); they have mass (due to interaction with the Higgs field); they have charges, but are not carriers of them. How would you define matter? What's missing?

Mar 27, 2018
Da Schneib,
The substance is formed from the substance Aether which fills the infinite universe.
Under the high vibrations of Aether, matter particles form, which are 3KG particles (3 quarks and 3 gluon binders). It is a "solid state" of matter. The second state of matter is "liquid" (free gluons). The "solid state" of matter and Aether cause gravity, and the "liquid state" of matter and Aether cause magnetism. All other stories and variants of science will be unsuccessful if this is not accepted. Higgs Field is a fictional theory, because science does not understand how they "found" this field.
Without free gluon and AETHER substance, there is no magnetism. This can be proven if a serious institution of science is interested. Therefore, the explanation is not a place here, because it is more important than 90% of the previous scientific knowledge.

Mar 27, 2018
Total word salad^^^^^^^
Wouldn't it be nice to be able to discuss an interesting science story, without wooists of various types hijacking it with their nonsense?

Mar 27, 2018
But @milnik, there is no need for Aether. We have fermions; electrons and up quarks and down quarks, mostly, with a few other things that show up occasionally. This description appears to everyone to explain everything to do with matter. What do you claim is missing? What thing does matter do that isn't explained?

Mar 27, 2018
we have kajmak, cheese, butter, do you think we do not need milk?

Mar 27, 2018
OK, I'll ask one more time, @milnik: what do you claim matter does that isn't explained by fermion behavior?

Mar 28, 2018
my explanations are under the sign of quotation: "", and these terms are: "solid" state of matter, and I stated that it is a 3KG particle, which consists of 3 quarks and 3 gluon binders. As this particle arises, we must know the structure of the universe and its control over all occurrences of matter and energy. The second state is a "liquid" state, and these are free gluons. It is not liquid, but it is the basic energy state from which, with Aether, everything is about magnetism.
 @ Schneib,
Science has given names to all forms, matter and energy, although it does not know who it originated from and how it originated. Here: particles are formed first: 3kg and free gluon. It is a quark gluon plasma from which magnetists are formed and the rest up to the supernova. When a free gluon enters a 3 kg particle, neutron stars (neutron stars) are formed.

Mar 28, 2018
And when the depletion of gluon decays, then in a 3kg particle it remains pozitron and proton forms, and the electron begins to circulate around the protons and that is the hydrogen atom. Is it clearer?

Mar 28, 2018
Wouldn't it be nice to be able to discuss an interesting science story, without wooists of various types hijacking it with their nonsense?

Well, to them scientific papers are word salad (because they don't understand the papers), but on some level they understand that scientific papers are written by really smart people. So now they think by posting word salad it makes them seem smart.

It's about as ridiculous as people who think dressing like their favorite movie star turns them into a movie star.

Of course, where it gets even more ridiculous is: whereas the movie star idea works on other people who don't know anything about movies there actually do exist people who do understand scientific papers. That Zeph and 'friends' are continually making total fools of themselves to everyone around them doesn't occur to them - because they cannot comprehend that others possess a modicum of intelligence whereas they themselves do not.

Read: they are cargo cultist.

Mar 28, 2018
it's my fault that I gave an explanation of this level because I see that you want to find out from me something that you could not get from all of the scientists and complete science so far. If you do not understand what the "solid state" of the matter means and the "fluid state" of matter, then it's difficult to prove to you. But you want to find out the truth from me, because so far you do not understand much, What I have put out is worth several Nobel Prizes. If you do not believe it, call the Nobel Committee and we will discuss it there, but do not ask me to explain to you what the whole science has no clue, and I am trying to put all of you on it to understand the new way of studying the universe and its appearance in it. the previous theories of non-volatile, inhuman, non-intrusive, unconscious, illogical, irresponsible, and they are against the existence of the one who formed us all.

Mar 29, 2018
anti and others: when the standard system does not fit, then the answers will likely come from left field. So never ignore that which is far afield and crackpot-ish in appearance and form.

It is the only place where the new (for established long term systems - which have the human tendency to take on religious form and function) has ever come from.

It can be tiresome, crazy, headache and vomitus inducing but it has always been that way.

The Prussians and the others vs Einstein's works - nearly came to blows, more than once. Lots of screaming, accusations, dismissals, and so on.

Gems and nuggets, every now and then. When the field is at fault, then - look far afield. Simple enough.

The danger of dismissal can lie with the negative proofing mindset (tied to the origins of religion in humans), which is the mark of an unevolved mind. Which is frightfully common. It's a human emotion problem, and has nothing to do with logic or logic's analysis.

Mar 29, 2018
It is the only place where the new (for established long term systems - which have the human tendency to take on religious form and function) has ever come from

You really don't get it, do you? ALL of science is left field. It's *science*. It is *by definition* coming from an unknown direction.

The only difference is: Brainfarting and actually working on a problem and coming up with a new idea are two separate things. Just throwing out 'brainfarts' isn't getting anyone anywhere. None of scientific breakthroughs of the past happened that way. Not Newton, not Einstein, not Dirac, not Laplace, not Fermi, not Feynman, not Schroedinger, not...

All of their breakthroughs came from a very solid understanding of the basics working within a framework that emphasizes consistency (math).

If you think science works any other way then you're just fooling yourself (or watching WAY too many Hollywood movies. )

Apr 03, 2018
Da Schneib, no-one is disputing the standard model of Quantum Physics, it is the beacon by which all models should be compared.

Right at the other end of the scale is the standard cosmological model, Lambda CDM, which does not predict anything that has not failed eg 'CDM' stands for 'Cold Dark Matter' although there is no evidence whatsoever that the Dark Matter phenomena is caused by particles of any kind, let alone cold ones. Dark Energy is an even more unlikely phenomena invented only to make the universe bend to the Big Bang model.

And the quantum part of the Big Bang is entirely incomplete with no part of it demonstrated beyond the wishful thinking of a few cosmologists eg no monopoles, no excuse given for the failure to explain why half the universe is not in the form of antimatter, no explanation for inflation, no evidence of multiple universe, no grand unifying theory etc.

Tribal religions, Big Bang & string theory are equidistant from the Standard Model.

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