16 thoughts on “Neutrino madness”

1. So, how is neutrino flux determined? Where does the astounding figure of “65 billion neutrinos per second” come from? Measured or estimated? If measured, how? If estimated, based on what model?

2. Historically, the neutrino is part of a fascinating chapter in the development of modern physics and our confidence in the Standard Model. Early 20th century studies of beta decay indicated possible violation of conservation of energy (and momentum). Even Niels Bohr hypothesized a real glitch in the law. Wolfgang Pauli, on the other hand, (in 1930) hypothesized an as yet unseen particle. That particle — the neutrino — was later experimentally confirmed (in 1956).

   Pauli … had opened the door to a whole new family of elementary particles— the neutrinos. That door is being flung open wider still as we type this paragraph: the subject of neutrinos is one of the hottest research topics in both particle physics and cosmology. We should add that experimentalists still often look for missing energy and momentum in their detectors in particle collisions, but this is always interpreted nowadays as evidence for a new particle, never as evidence for the breakdown of the conservation laws of energy and momentum [and charge]. Our … confidence … in the symmetries of the structure of space and time, and Noether’s theorem would, at this point, be very hard to shake. — Lederman, Leon M.; Hill, Christopher T. (2011-11-29). Symmetry and the Beautiful Universe (p. 109). Prometheus Books. Kindle Edition.

3. Fermilab’s “Doc Don” presents an overview of the neutrino in this YouTube 5 minute video “Neutrinos: Nature’s Ghosts?”

   Published on Jun 18, 2013
   Dr. Don Lincoln introduces one of the most fascinating inhabitants of the subatomic realm: the neutrino. Neutrinos are ghosts of the microworld, almost not interacting at all. In this video, he describes some of their properties and how they were discovered. Studies of neutrinos are expected to be performed at many laboratories across the world and to form one of the cornerstones of the Fermilab research program for the next decade or more.

   Neutrinos originate from nuclear reactions and the biggest nuclear reactor around is the Sun. The Sun emits so many neutrinos that even though it is about 93 million miles away, something like 650 trillion neutrinos from the Sun hit you every second. So suppose you wanted to shield yourself from that steady barrage of neutrinos. How would you do that? Well, if you took a huge block of solid lead that extended to the nearest star…and I’m not talking about the Sun, I’m talking about Alpha Centauri, which is about 5 light years away, you’d be able to block something like half the neutrinos from the Sun. If five light years of solid lead is such a poor shield, then there is no way that you can stop them…even if you used the entire Earth as your protection. Most neutrinos blow right through the planet like it’s not even there.

4. The YouTube video of Nobel laureate Art McDonald’s public lecture “A Deeper Understanding of the Universe from 2 km Underground” at the Perimeter Institute for Theoretical Physics on April 13, 2016, provides a good overview of neutrino research. McDonald shared the 2015 Nobel prize in physics “for the discovery of neutrino oscillations, which shows that neutrinos have mass.” He presents an overview of his personal journey studying the “ghost particle” and establishing the underground research facility for that purpose.

5. 7-22-2017 – Here’s an article about the latest planned advance in neutrino research: Creating the largest neutrino detectors in the world.

   A new era in neutrino physics in the United States is underway, and UW–Madison’s Physical Sciences Laboratory (PSL) in Stoughton is playing a key role.

   The Long-Baseline Neutrino Facility, home to the $2 billion Deep Underground Neutrino Experiment (DUNE), will eventually send particles 800 miles through the earth from a lab outside Chicago to a mile-deep detector in an inactive gold mine in the Black Hills of South Dakota.

   Neutrinos are little-understood, but their role in understanding matter and the dynamics of the universe is growing as science continues to learn more about the enigmatic particles through a constellation of new and exotic detectors, including the new DUNE experiment.

   Groundbreaking ceremonies for the Long-Baseline Neutrino Facility (LBNF) will be held simultaneously today at the Sanford Lab in South Dakota and at Fermilab in Illinois.

6. Space.com posted another article yesterday about neutrino research at the IceCube lab in Antarctica: “Ghostly Cosmic Neutrinos Are Stopped Cold by Planet Earth, New Study Shows.”

   Researchers from the IceCube experiment in Antarctica announced this week that they have measured the rate at which high-energy neutrinos interact with regular matter instead of passing through unencumbered.

   “Understanding how neutrinos interact is key to the operation of IceCube,” Francis Halzen, a professor of physics at the University of Wisconsin-Madison and the IceCube principal investigator, said in a statement from the university.

   So, what makes some neutrinos so much more energetic? (How is the energy bundled differently? What does the Standard Model say?)

   Most of those neutrinos come from the sun, which releases a constant stream of low-energy neutrinos out into space.

   The neutrinos that IceCube is seeking — those from cosmic sources — are almost a million times more energetic than solar neutrinos.

7. Sterile neutrino?

   Another update on neutrino research by Don Lincoln (Senior Scientist, Fermi National Accelerator Laboratory; Adjunct Professor of Physics, University of Notre Dame) in this Space.com article (June 19, 2018) [originally published on Live Science], “The 4th Flavor? Scientists Close in on a New Kind of Neutrino.”

   A study in 2001 conducted at the Los Alamos laboratory by a collaboration called LSND (Liquid Scintillator Neutrino Detector) stood out. Their measurement didn’t fit into the accepted picture of three different flavors of neutrinos. To get their results to make sense, they needed to hypothesize a fourth type of neutrino. And this wasn’t an ordinary kind of neutrino. It is called a “sterile neutrino,” which means that, unlike ordinary neutrinos, it didn’t feel the weak force. But it did participate in neutrino oscillation … the morphing of neutrino flavors. And it was probably heavy, which means that it was an ideal candidate for dark matter.

   And now we get to the recent measurement by the MiniBooNE [Mini BOOster Neutrino Experiment] experiment at Fermilab. …

   MiniBooNE scientists found that their data actually supported the LSND measurement and, further, if they combined their data with the LSND data, the statistical strength of the measurement is strong enough to claim a discovery … possibly of sterile neutrinos.

   So, how do we resolve this? How do we find out who is right? Well, this is science and, in science, measurement and replication win the argument.

8. This Symmetry Magazine article (10/25/2018) also summarizes neutrino particle research and the Standard Model: “Already beyond the Standard Model — We already know neutrinos break the mold of the Standard Model. The question is: By how much?”

   … in the search for physics beyond the Standard Model, one area of notably keen interest continues to be neutrinos.

   This extra neutrino — suggested by results from the Liquid Scintillator Neutrino Detector and the MiniBooNE experiment — wouldn’t match up with the generations of particles in the Standard Model. It would be “sterile,” meaning it likely wouldn’t interact directly with any Standard Model particles. It might even be a form of dark matter.

   Meanwhile, other oscillation experiments will continue to understand what gave neutrinos their mass in the first place — one of the first hints we have had of physics beyond the Standard Model.

9. This Gizmodo article summarizes the results of a recent neutrino experiment:”Dark Matter Detector Makes Incredible Neutrino Observation” by Ryan F. Mandelbaum (4-25-2019).

   The hunt for the most popular dark matter candidate has so far turned up empty. But one of these dark matter experiments, called XENON1T, has now observed a process … that will hopefully help scientists better understand the shadowy particle called the neutrino.

   Scientists are pretty sure that the second most abundant particle in the Universe (after photons, particles of light) is the neutrino. … There are a ton of neutrino mysteries to solve. The new measurement, called “two-neutrino double electron capture,” is an important stepping stone to providing those answers.

   In the process, two protons in the atomic nucleus spontaneously and simultaneously absorb a pair of electrons orbiting the nucleus, releasing a pair of neutrinos. The experimental signature of the event is a barrage of x-rays and electrons resulting from other electrons orbiting the atom replacing the two absorbed by the nucleus. And when I say rare, I mean rare. The average amount of time it would take half of the xenon atoms in a sample to undergo this reaction is 1.8 × 1022 years, … roughly a trillion times the age of the Universe.

   After 214 days of observing (177 days of usable data), the researchers’ analysis revealed approximately 126 two-neutrino double electron capture events.

   Researchers aren’t calling their results a “discovery,” because their statistics didn’t hit the five-standard deviation threshold particle physicists require in order to use that word. Instead, they’re calling it an “observation,” …

   Additional information

   Space.com: “The Quest to Find One of the Most Elusive Particle Decays in the Universe” by Paul Sutter (April 26, 2019).

   One of these elusive radioactive decays has never actually been seen, but physicists are really hoping to find it. Called neutrinoless double-beta decay, it would mean radioactive elements spit out two electrons and nothing else (not even ghostly, chargeless, barely-there particles known as neutrinos). If physicists manage to spot this decay in the real world, it would violate one of the fundamental rules of physics and fuel a race to find new ones.

10. This U.S. Department of Energy podcast / article “S3 E7: DUNE: The Neutrinos Must Flow” (May 7, 2019) discusses the key role neutrinos play in the Standard Model regarding explaining why anything exists — why the symmetries of the Big Bang did not just result in matter and anti-matter annihilating, leaving nothing — as least no matter, only a “bath of energy.” This article contains some interesting pictures and [visualization] videos, as well as a transcript of the podcast. Over a 1000 scientists from around the world … a “megascience” experiment.

    Join Direct Current on a subatomic sojourn into the Deep Underground Neutrino Experiment (DUNE), a massive international research project aiming to unlock the secrets of the neutrino with help from more than 175 institutions in over 30 countries.

    We’ll take you from Fermilab to the home of the Large Hadron Collider in Switzerland to the bottom of a former gold mine a mile beneath the hills of South Dakota as we explore one of the most ambitious particle physics projects of our lifetime.

    From transcript:

    MAN’S VOICE: “Deep in the human unconscious is a pervasive need for a logical universe that makes sense. But the real universe is always one step beyond logic.” — Dune, by Frank Herbert.

    KREER: Neutrinos are the stars of the lab’s current research efforts. Bonnie is one of more than a thousand scientists from around the world involved in this “megascience” project called the Deep Underground Neutrino Experiment, or “DUNE.” There’s no connection to the Frank Herbert sci-fi classic we quoted at the start of the show.

    KREER: We’re steering clear of dark matter this time around. There’s plenty to cover with neutrinos. As Bonnie said, neutrinos are everywhere, and they are connected to the stuff you are probably familiar with: things like protons, neutrons, and electrons. 

    FLEMING: There’s so many things I’m excited about. The first thing I’m excited about is the general question that we’re addressing, which is basically, are neutrinos the reason we exist? On the most fundamental scale. Are there differences between matter and antimatter? And can we find those differences and explain why we live in a matter-dominated universe? 

    DOZIER: The secret to that could lie with something really odd about the way neutrinos behave [neutrino oscillation].

    MERMINGA: The protons that we’re accelerating — we’re accelerating them at very high energy (800 million electron volts) and we’re accelerating a lot of them, so the intensity is very high as well. Think about the lightbulb in your house, which is just 60 watts for example. Now the beam of protons will have power that is starting at 1.2 million watts.

    KREER: The project that Lia is helping direct right here in the U.S. has the potential to be as much a pioneer in particle physics — and to our understanding of the universe — as CERN’s Large Hadron Collider in Switzerland. Except in the case of Fermilab, the new ground being broken — literally and figuratively — centers around the neutrino.

    References:

    Fermilab: “Long-Baseline Neutrino Facility pre-excavation work is in full swing” (May 2, 2019).

    Fermilab > Youtube: “Small Particles, Big Science: The International LBNF/DUNE Project” (March 28, 2016).

    Neutrinos are the most abundant matter particles in the universe, yet very little is known about them. This animation shows how the Department of Energy’s Long-Baseline Neutrino Facility will power the Deep Underground Neutrino Experiment to help scientists understand the role neutrinos play in the universe. DUNE will also look for the birth of neutron stars and black holes by catching neutrinos from exploding stars. More than 800 scientists from 150 institutions in 27 countries are working on the LBNF/DUNE project, including Armenia, Belgium, Brazil, Bulgaria, Canada, Colombia, Czech Republic, Finland, France, Greece, India, Iran, Italy, Japan, Madagascar, Mexico, Netherlands, Peru, Poland, Romania, Russia, Spain, Switzerland, Turkey, Ukraine, United Kingdom, USA.

11. Phys.org > Theorists discover the ‘Rosetta Stone’ for neutrino physics by Stephen Parke, Fermi National Accelerator Laboratory (September 24, 2019).

    The identity [newly discovered fundamental identity in linear algebra] relates eigenvectors and eigenvalues in a direct way that hadn’t been previously recognized. Eigenvectors and eigenvalues are two important ways of reducing the properties of a matrix to their most basic components and have applications in many math, physics and real-world contexts, such as in analyzing vibrating systems and facial recognition programs. The eigenvectors identify the directions in which a transformation occurs, and the eigenvalues specify the amount of stretching or compressing that occurs.

    The physics usage case of this result stems from our investigations of neutrino oscillation probabilities in matter, which involve finding eigenvectors and eigenvalues, both of which are rather complicated expressions. While the eigenvalues are somewhat unavoidably tricky, this new result shows that the eigenvectors can be written down in a simple, compact, and easy-to-remember form, once the eigenvalues are calculated. For this reason, we called the eigenvalues “the Rosetta Stone” for neutrino oscillations in our original publication – once you have them, you know everything you want to know.

12. Gizmodo > A Huge Experiment Has ‘Weighed’ the Tiny Neutrino, a Particle That Passes Right Through Matter by Ryan F. Mandelbaum (9/18/2019)

    An experiment nearly two decades in the making has finally unveiled its measurements of the mass of the universe’s most abundant matter particle: the neutrino.

    “You don’t get a lot of chances to measure a cosmological parameter that shaped the evolution of the universe in the laboratory,” Diana Parno, an assistant research professor at Carnegie Mellon University who works on the experiment, told Gizmodo.

    The mere fact that [neutrino] oscillation exists sets a lowest possible average mass of the three mass states, less than 0.1 electron volts (eV). After a month of operating and 18 years of planning and construction, KATRIN has now predicted an upper limit of any of the three mass states at 1.1 eV, where an electron weighs around 500,000 eV and a proton weighs nearly a billion.

    … KATRIN’s findings are valuable because they don’t rely on grand theories of how the universe works …

13. As previously noted, neutrino research is quite an active field. Big science. In particular, addressing a question posed in the cosmological model of the Big Bang theory: why does the universe contain something (matter) rather than nothing (a mere void from matter-antimatter annihilation). One of the unsolved problems in physics – matter–antimatter (baryon) asymmetry.

    This Quanta Magazione article (among others) discusses accumulating evidence of a key imbalance between neutrinos and antineutrinos.

    Quanta Magazine > “Neutrino Asymmetry Passes Critical Threshold” by Natalie Wolchover (April 15, 2020).

    The T2K team [in Japan] started seeing signs of a discrepancy in the behavior of neutrinos and antineutrinos in 2016. Their new result, following years of additional data collection and improvements to the data-analysis techniques, rises to a statistical level that physicists regard as official evidence of a physical effect. “The significance of [the effect] increases with the collected data, which is what one expects when the result is correct,” said Werner Rodejohann, a neutrino physicist at the Max Planck Institute for Nuclear Physics in Germany who was not involved in the experiment.

    The data implies that neutrinos have a higher probability of oscillating [between “flavors”] than antineutrinos, a distinction expressed by a quantity called the CP-violating phase. If this phase were zero and neutrinos and antineutrinos behaved the same, the experiment would have detected roughly 68 electron neutrinos and 20 electron antineutrinos. Instead, it found 90 electron neutrinos and only 15 electron antineutrinos — highly skewed results indicating that the CP-violating phase could be as large as theoretically possible.

    Future, bigger experiments — one called DUNE in the U.S. that will begin operations in 2027, as well as T2K’s planned successor, known as T2HK — should be able to nail the value of the CP-violating phase.

14. More articles on neutrinos.

    • Phys.org > “Where neutrinos come from” by Moscow Institute of Physics and Technology (May 13, 2020) – The Russian RATAN-600 telescope helps to understand the origin of cosmic neutrinos.

    High-energy neutrinos are created when protons accelerate to nearly the speed of light.

    The Russian astrophysicists focused on the origins of ultra-high-energy neutrinos at 200 trillion electron volts or more. The team compared the measurements of the IceCube facility, buried in the Antarctic ice, with a large number of radio observations. The elusive particles were found to emerge during radio frequency flares at the centers of quasars.

    • History of the Neutrino > Neutrino properties

    Neutrinos can interact only through the weak interaction. It allows them to pass through the Sun or Earth without any deviation or so. This makes their detection very difficult and it requires large masses for the detectors and large neutrino fluxes from the sources.

15. Although “every neutrino and antineutrino we’ve ever observed moves at speeds so fast they’re indistinguishable from the speed of light,” are there slower neutrinos? Especially if neutrino energy varies?

    • Forbes > “Ask Ethan: Do Neutrinos Always Travel At Nearly The Speed Of Light?” by Ethan Siegel, Senior Contributor (Aug 28, 2020)

    (image caption) Neutrino detectors, like the one used in the BOREXINO collaboration here, generally have an enormous tank that serves as the target for the experiment, where a neutrino interaction will produce fast-moving charged particles that can then be detected by the surrounding photomultiplier tubes at the ends. However, slow-moving neutrinos cannot produce a detectable signal in this fashion. INFN / BOREXINO COLLABORATION

    … experimentally, we simply don’t have the capabilities to detect these slow-moving neutrinos directly. Their cross-section is literally millions of times too small to have a chance at seeing them, as these tiny energies wouldn’t produce recoils noticeable by our current equipment. Unless we could accelerate a modern neutrino detector to speeds extremely close to the speed of light, these low-energy neutrinos, the only ones that should exist at non-relativistic speeds, will remain undetectable.

16. Here’s an overview of how the DUNE project makes neutrino “beams.” Sort of the trick to herding cats (which tend to move in all directions). And using the stopping power of planet Earth for a cleaner detector signal.

    • Big Think > “Ask Ethan: How can physicists make neutrino beams?” by Ethan Siegel (July 8, 2022) – The ghostly neutrino rarely interacts with matter, so how well can we truly make “beams” out of them?

    … the neutrino and antineutrino … need something like a light-year’s worth of lead to have a 50/50 shot of interacting with it.

    … the primary way we produce neutrinos is either through fusion/fission reactions, or by creating another, heavier, unstable particle that will decay.

    DUNE’s CENTER-OF-MOMENTUM (COM) FRAME

    In particle colliders, … the particles to be collided are circulated in opposite directions with equal (and opposite) momenta, these collisions also produce a random, evenly distributed set of daughter particles. When unstable particles like the Z-boson, W-boson, the charged pion, or heavy leptons like the muon or tau decay, they produce neutrinos as well; since they’re moving in random directions, so do the neutrinos.

    If, instead of colliding particles with a lot of kinetic energy into other particles moving with equal amounts of kinetic energy but moving in opposite directions, we collided particles with high kinetic energies into particles at rest, we’d get a narrowly collimated cone of particles: effectively, a beam!

    By accelerating protons … the next step is to smash them into what we call a “fixed target,” which is a sacrificial piece of material that you don’t mind destroying by smashing high-energy protons into it. A block of acrylic or graphite, for example, will do just fine.

    This is exactly what we want to happen, and ideally, we want all of these decays [pions > muons > electrons/positrons + neutrinos] to happen before the makeshift “beam” we’ve created strikes the Earth. … By collimating the charged particles with electromagnets before they decay, you can make the neutrino beam even narrower.

    
    Image credit: DOE/Fermilab

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