This Is Why Neutrinos Are The Standard Model’s Greatest Puzzle
“But this is where the big puzzle comes in: if neutrinos and antineutrinos have mass, then it should be possible to turn a left-handed neutrino into a right-handed particle simply by either slowing the neutrino down or speeding yourself up. If you curl your fingers around your left thumb and point your thumb towards you, your fingers curl clockwise around your thumb. If you point your left thumb away from you, though, your fingers appear to curl counterclockwise instead.
In other words, we can change the perceived spin of a neutrino or antineutrino simply by changing our motion relative to it. Since all neutrinos are left-handed and all antineutrinos are right-handed, does this mean that you can transform a left-handed neutrino into a right-handed antineutrino simply by changing your perspective? Or does this mean that left-handed anti-neutrinos and right-handed neutrinos exist, but are beyond our current detection capabilities?”
Every fermion in the Standard Model has a number of properties inherent to it. Mass, charge, baryon number, lepton number, lepton family number, etc. All the fermions that exist in the Standard Model have non-zero masses, even the neutrino, and all of them can have their intrinsic angular momentum go in any direction… except the neutrino. Unlike all the other fermions, we’ve only ever seen left-handed neutrinos and right-handed antineutrinos. But if we’re clever enough, we can design an experiment that will reverse the perceived spin of these neutrinos.
What will we see then? Believe it or not, the answer could unlock the mystery of why our Universe is filled with matter and not anti-matter. Let’s do what we can to solve this puzzle; the entire Universe may be at stake!
Is There Really A Fourth Neutrino Out There In The Universe?
“Regardless of what the ultimate explanation is, it’s quite clear that the normal Standard Model, with three neutrinos that oscillate between electron/muon/tau types, cannot account for everything we’ve observed up to this point. The LSND results, once dismissed as a baffling experimental result that must surely be wrong, have been confirmed in a big way. With reactor deficiencies, MiniBooNe’s results, and three new experiments on the horizon to gather more data about these mysteriously misbehaving particles, we may be poised for a new revolution in physics.
The high-energy frontier is only one way we have of learning about the Universe on a fundamental level. Sometimes, we just have to know what the right question to ask truly is. By looking at the lowest-energy particles at different distances from where they’re generated, we just might take the next great leap in our knowledge of physics. Welcome to the era of the neutrino, which is taking us, at last, beyond the Standard Model.”
No matter how good, compelling, elegant, or successful our theories about the Universe are, they must always be confronted with experiments. If there’s a new, conflicting experimental result, it must be verified and validated independently to make sure it’s correct. Well, that was what the LSND experiment was for neutrinos and the Standard Model: an outlier that couldn’t be explained consistently with the other observations. After 16 years, the MiniBooNe experiment has released their final results: validating LSND and presenting a combined 6.0-sigma significance. Neutrinos don’t behave as they should.
Does that mean there’s a 4th neutrino? That one is sterile? That the Standard Model is wrong? It’s a fascinating topic, and you should get the full story today!
How A Failed Nuclear Experiment Accidentally Gave Birth To Neutrino Astronomy
“The scientific importance of this result cannot be overstated. It marked the birth of neutrino astronomy, just as the first direct detection of gravitational waves from merging black holes marked the birth of gravitational wave astronomy. It was the birth of multi-messenger astronomy, marking the first time that the same object had been observed in both electromagnetic radiation (light) and via another method (neutrinos).
It showed us the potential of using large, underground tanks to detect cosmic events. And it causes us to hope that, someday, we might make the ultimate observation: an event where light, neutrinos, and gravitational waves all come together to teach us all about the workings of the objects in our Universe.”
When you build an experiment to look for an effect you’ve never seen before, it’s an extremely risky endeavor. If what you’re expecting to find is actually there, the payoff is tremendous: like the LHC finding the Higgs. If there’s nothing to find, like the direct detection searches for WIMP dark matter, the null result can be viewed as a colossal (and expensive) failure. One such failure was the construction of an enormous, 3,000+ ton detector facility to look for proton decays. The proton, as you may have heard, is stable, so in that regard, the experiments looking for decays were wildly unsuccessful. But that same setup is extremely sensitive to neutrinos, and in 1987, we used a nucleon decay experiment to successfully find the first neutrinos from beyond the Milky Way!
Come get the story of KamiokaNDE, and learn how it went from being an unsuccessful nucleon decay experiment to the birth of multi-messenger astronomy!
How Neutrinos Could Solve The Three Greatest Open Questions In Physics
“Perhaps ironically, the greatest advance in particle physics — a great leap forward beyond the Standard Model — might not come from our greatest experiments and detectors at high-energies, but from a humble, patient look for an ultra-rare decay. We’ve constrained neutrinoless double beta decay to have a lifetime of more than 2 × 1025 years, but the next decade or two of experiments should measure this decay if it exists. So far, neutrinos are the only hint of particle physics beyond the Standard Model. If neutrinoless double beta decay turns out to be real, it might be the future of fundamental physics. It could solve the biggest cosmic questions plaguing humanity today. Our only choice is to look. If nature is kind to us, the future won’t be supersymmetry, extra dimensions, or string theory. We just might have a neutrino revolution on our hands.”
When we look at the Standard Model of particle physics, there’s a big problem that leaps out at us right away: it works well. It works so practically perfectly well that it leaves us very little room for solving some of the problems we have in the Universe: problems like dark matter, dark energy, and the origin of matter. The only hint we have that the Standard Model isn’t fully correct comes from our observations of neutrinos: they have very tiny masses, and they oscillate from one flavor into another. Furthermore, they only come in one chirality: neutrinos are always left-handed and anti-neutrinos are always right-handed. This could be explained if neutrinos weren’t normal (Dirac) fermions like the other Standard Model particles, but were their own antiparticles, and behaved as Majorana fermions. If this scenario is true, it could not only solve the dark matter, dark energy, and matter/antimatter asymmetry problems all at once, but there’s an experimental signature we can look for.
That experiment is running right now! While the LHC is all the rage as far as looking for new physics goes, neutrinoless double beta decay just might bring about the future of fundamental physics.
Five Discoveries In Fundamental Physics That Came As Total Surprises
“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
It’s often said that advanced in physics aren’t met with “eureka!” but rather with “that’s funny,” but the truth is even stranger sometimes. Rather than the scientific method of: hypothesis, method, experiment, results, conclusion, revise, repeat, etc., many times throughout history, it’s been a series of surprise observations that have often led to our greatest leaps forward. When the speed of light was discovered not to differ when you moved with or against it, it was so revolutionary it was the only Nobel Prize ever awarded for a null result. When the gold foil experiment resulted in high-energy recoils, it surprised Rutherford so thoroughly it was the most incredible thing to ever happen to him in his life. The leftover glow from the Big Bang was discovered quite by accident; the neutrino was a crazy hypothesis that many abandoned; and the discovery of the muon, perhaps the most unexpected particle of all, literally was met with a cry of, “who ordered that?” from Nobel Laureate I.I. Rabi.
These five discoveries changed the course of physics forever, but they came as total surprises to practically everyone. Sometimes, the answer is in the place you least expect.
Break The Standard Model? An Ultra-Rare Decay Threatens To Do What The LHC Can’t
“Just by sitting around with a bunch of unstable atoms, waiting for them to decay and measuring the decay products to incredible accuracy, we have the potential to finally break the Standard Model. Neutrinos are already the one type of particle known to go beyond the original Standard Model predictions, with potential ties to dark matter, dark energy, and baryogenesis in addition to their mass problem. Discovering that they undergo this bizarre, never-before-seen decay would make them their own antiparticles, and would introduce Majorana Fermions into the real world. If nature is kind to us, a box full of radioactive material might at last do what the LHC can’t: shed light on some of the deepest, most fundamental mysteries about the nature of our Universe.”
Want to uncover the secrets to the Universe? Find out what particles and interactions there are beyond the Standard Model? The conventional approach is to take particles up to extremely high energies and smash them together, hoping that something new and exciting comes out. That’s a solid approach, but it has its limits. In particular, we haven’t seen anything new at the LHC other than the Higgs Boson, and might not even if we run it forever. But another, more subtle approach might yield heavy dividends: simply gathering a very large number of unstable atoms and looking for a special type of decay: neutrinoless double beta decay. If this decay actually occurs in nature, it would mean that neutrinos aren’t like the other particles we know of, but rather that neutrinos and antineutrinos are the same particles: Majorana particles!
What would all of this mean, and what would it teach us about our Universe? Find out about our simplest hope for going beyond the Standard Model today!
When Will The First Star Go Dark?
“I’m sorry to disappoint you, but there aren’t any black dwarfs around today. The Universe is simply far too young for it. In fact, the coolest white dwarfs have, to the best of our estimates, lost less than 0.2% of their total heat since the very first ones were created in this Universe. For a white dwarf created at 20,000 K, that means its temperature is still at least 19,960 K, telling us we’ve got a terribly long way to go, if we’re waiting for a true dark star.”
Stars live for a variety of ages, from just a million or two years for some to tens of trillions of years for others. But even after a star has run out of its fuel and died, its stellar corpse continues to shine on. Neutron stars and white dwarfs are both extremely massive, but very small in volume compared to a star. As a result, they cool very slowly, so slow that a single one has not yet gone dark in all the Universe. So how long will it take, and who will get there first: neutron stars or white dwarfs? Believe it or not, there’s still enough uncertainty about how neutron stars cool, mostly due to uncertainties in neutrino physics, that we think we know the answer to be white dwarfs – and 10^14 or 10^15 years – but we’re not entirely sure!
Come find out what we know about finding the first truly dark star in the Universe today.