- 3513 - NEUTRINOS - a lot to learn! How do you test theories of the universe? Scientists have built the largest-ever cosmic simulation to include tiny "ghost" particles called “neutrinos“. To explore one of physics' biggest unsolved mysteries, the researchers used a 7 million CPU cores to solve for the evolution of 330 billion particles and a computational grid of 400 trillion units. That’s a lot.
--------------------- 3513 - NEUTRINOS - a lot to learn!
- By far the most important form of matter in the universe is dark matter. It makes up about 80% of all matter. “Baryonic matter” is the stuff that makes up stars, planets and the rich variety of the entire periodic table. But it makes up just a small fraction of all the “matter” in the universe.
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- Therefore, “Dark Matter” forms the backbone of the cosmos. But what is it? Billions of years ago, there were no structures in the universe. All of the matter was smoothly distributed, and not lumpy at all. There simply weren't very many variations in density from place to place.
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- But with time there were tiny density differences, seeded from microscopic quantum fluctuations in the early seconds of the Big Bang. Places with slightly higher density had slightly more gravity, and that's where dark matter began to pool together. As those early structures budded, they attracted even more material.
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- Over billions of years, this process emptied out vast regions of the universe, now known as cosmic voids, pulling all the matter into an extensive network of clusters, walls and filaments.
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- There are neutrinos, extremely tiny particles that have barely any mass. They make up less than 0.1% of all the mass in the universe. But these minuscule particles have an outsize influence on the evolution of structures. They are fast, capable of traveling at nearly the speed of light. This incredible speed dampens the formation of large structures, such as galaxies and clusters.
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- Dark matter wants to keep piling up through gravity, neutrinos go too fast to settle down in one spot. And although neutrinos have very little mass, they still have some mass. They can use their gravity to weakly influence the behavior of dark matter, thus preventing it from clumping as tightly as it normally would. The universe is a little smoother than it would be without neutrinos.
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- Finding the masses of the three known neutrino "flavors" , electron neutrinos, muon neutrinos and tau neutrinos, is a major unsolved problem in modern physics. Ironically, we can measure the masses of these tiny particles by mapping the largest structures in the universe.
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- If you change the neutrino mass just a bit in computer simulations, it will change how the neutrinos influence the formation of structures over billions of years. So by measuring those same structures, we can get an understanding of neutrino mass.
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- These simulations usually encompass a small fraction of the real universe and start with a set of dark matter "particles," with each particle representing a certain amount of dark matter. The simulations track how those particles evolve through their mutual gravity, giving rise to the giant structures we see today.
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- Simulating neutrinos is more difficult because of their ridiculous speed. They used 7 million processors on the “Fugaku supercomputer” to trace the evolution of dark matter and the influence of neutrinos on the formation of structures. The researcher used 330 billion particles to represent dark matter and a computational grid of 400 trillion components to represent neutrinos, in the largest simulation of its kind.
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- Our best models of particle physics is bursting at the seams as it struggles to contain all the weirdness in the universe. Now there is a series of strange events in Antarctica. Strange results from laboratory experiments suggest flickers of ghostly new species of neutrinos beyond the three described in the Standard Model.
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- The universe seems full of dark matter that no particle in the Standard Model can explain.
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- Three times since 2016, ultra-high-energy particles have blasted up through the ice of Antarctica, setting off detectors in the “Antarctic Impulsive Transient Antenna “(ANITA) experiment, a machine dangling from a NASA balloon far above the frozen surface.
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- Those events along with several additional particles detected later at the buried “Antarctic neutrino observatory IceCube” don't match the expected behavior of any Standard Model particles.
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- The particles look like ultra high-energy neutrinos. But ultra high-energy neutrinos shouldn't be able to pass through the Earth. That suggests that some other kind of particle, one that's never been seen before, is flinging itself into the cold southern sky.
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- These particles are from cosmic accelerators which are giant neutrino guns hiding in space that periodically fire intense neutrino bullets at Earth. A collection of hyperactive neutrino guns somewhere in our northern sky could have blasted enough neutrinos into Earth that we'd detect particles shooting out of the southern tip of our planet.
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- Neutrinos pass through our planet all the time, mostly coming from the sun and rarely, if ever, colliding with the protons, neutrons and electrons that make up our bodies and the dirt beneath our feet.
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- Ultra-high-energy neutrinos from deep space are different from their low-energy cousins. Much rarer than low-energy neutrinos, they have wider "cross sections," meaning they're more likely to collide with other particles as they pass through them. The odds of an ultra-high-energy neutrino making it all the way through Earth intact are so low that you'd never expect to detect it happening.
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- Many ultra-high-energy cosmic neutrinos come from the interactions of cosmic rays with the “cosmic microwave background” (CMB), the faint afterglow of the Big Bang. Every once in a while, those cosmic rays interact with the CMB in just the right way to fire high-energy particles at Earth.
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- This is called the "flux," and it's the same all over the sky. Both ANITA and IceCube observatories have already measured what the cosmic neutrino flux looks like to each of their sensors, and it just doesn't produce enough high-energy neutrinos that you'd expect to detect a neutrino flying out of Earth at either detector even once.
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- “Blazars“, active galactic nuclei, gamma-ray bursts, starburst galaxies, galaxy mergers, and magnetized and fast-spinning neutron stars are all good candidates for those sorts of accelerators.
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- We know that cosmic neutrino accelerators do exist in space. In 2018, IceCube tracked a high-energy neutrino back to a “blazar“, an intense jet of particles coming from an active blackhole at the center of a distant galaxy.
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- ANITA picks up only the most extreme high-energy neutrinos. If the upward-flying particles were cosmic-accelerator-boosted neutrinos from the Standard Model, most likely the energy “tau neutrinos” then, the beam should have come with a shower of lower-energy particles that would have tripped IceCube's lower-energy detectors.
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- Many possibilities seem to fit the limited data, including a fourth species of "sterile" neutrino outside the Standard Model and a range of theorized types of dark matter.
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- Researchers have detected neutrino candidates produced by the “Large Hadron Collider” (LHC) at the CERN facility near Geneva, Switzerland. In a major milestone in particle physics, researchers in a new study report observing six neutrino interactions during an experiment at the LHC.
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- Neutrinos are subatomic particles that have a very small mass like an electron but have no electrical charge, a characteristic that has made them extremely challenging to detect.
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- The LHC includes four main detectors: ALICE, ATLAS, CMS and LHCb. It works by colliding two high-energy particle beams with one another close to the speed of light. When the charged particles, like protons, smash into one another at such high speeds, the energy of the impact becomes matter in the form of new particles or subatomic particles. So, the LHC can essentially "produce" subatomic particles.
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- A new emulsion detector instrument that is made up of dense metal plates of lead and tungsten interspersed with layers of emulsion. Emulsion plates or layers, in physics, work a lot like old-school photography film. When film strips are exposed to light, photons show themselves as images as the film develops. Similarly, with this instrument, when exposed to the particle collisions, the emulsion layers revealed neutrino interactions after being processed.
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- Particles colliding during this test produced neutrinos that then smashed into nuclei in the dense metal of the plates. The resulting particles traveled through emulsion layers and created observable "imprints" left behind.
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- This reported detection of neutrino interactions reveals two major things:
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- It verified that the position forward of the ATLAS interaction point at the LHC is the right location for detecting collider neutrinos.
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- It demonstrated the effectiveness of using an emulsion detector to observe these kinds of neutrino interactions.
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- CERN is expected to be able to record more than 10,000 neutrino interactions in the next run of the LHC, beginning in 2022.
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- CERN is also working towards an experiment with “FASER instruments” to try and detect "dark photons," which scientists expect to reveal the behavior and nature of dark matter.
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- When the universe was born nearly 14 billion years ago, it contained equal amounts of matter and its counterpart, antimatter. Antimatter particles have the same mass as their "normal" cousins but opposite electrical charges. A duo such as the electron (normal, negatively charged) and the positron (antimatter, positively charged).
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- When matter and antimatter particles collide, they annihilate with perfect efficiency, converting into 100% pure energy. And, therein lies the mystery: If there were an equal number of particles and antiparticles at the universe's birth, they should all have found and annihilated each other, leaving our cosmos utterly bereft of each.
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- But that obviously didn't happen, as your existence clearly shows. There ended up being a tiny excess of matter over antimatter, just a single particle per billion matter-antimatter pairs.
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- Physicists have gathered some clues about this excess-matter mystery over the years. They figured out that quarks and antiquarks don't behave in exactly the same way. But this violation of "charge-conjugation parity-reversal symmetry," or “CP symmetry” for short, wasn't substantial enough to explain the matter-antimatter disparity.
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- “Leptons” are subatomic particles that includes electrons, muons, tau particles and neutrinos. Quarks and leptons, in turn, are “fermions“, one of the two main categories of subatomic particles. The other category is “bosons“, which include force-carrying particles such as the photon, the gluon, the Higgs and the unconfirmed graviton.
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- The vast majority of the beam particles zoom through Earth like our planet's not even there. But a few get flagged by an underground detector at “Kamioka Observatory“. This detector is a tank filled with 55,000 tons of very pure water. When a neutrino interacts with a neutron in the tank, a muon or an electron can be produced. And sensitive equipment picks these secondary particles up.
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- Such detections contain a lot of information. As neutrinos travel, they oscillate between three different "flavors": electron, muon and tau. And the flavor type determines what secondary particle is produced during a collision with a neutron.
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- The “T2K Collaboration” project analyzed data gathered from 2009 to 2018. The researchers report that they found evidence that neutrinos and antineutrinos oscillate in different ways.
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- The results exclude CP conservation (that suggest that CP violation has occurred) at a 95% confidence level, and show that the CP-violating parameter is likely to be large. These results could be the first indications of the origin of the matter–antimatter asymmetry in our universe.
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- Several next-generation neutrino experiments are already in the works. Japan's “T2HK“, which will be similar to but more powerful than T2K, February, 2022, and the “Deep Underground Neutrino Experiment” (DUNE), which will employ a beam at Fermilab and detectors there and in South Dakota.
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- T2HK and DUNE will provide complementary techniques and measurements. What will we learn next?
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March 22, 2022 NEUTRINOS - a lot to learn! 3513
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