By Doug Cowen, Penn State
Uncommon neutrinos discovered with the assistance of ice
A few trillion tiny particles referred to as neutrinos go via you each second. Created in the course of the Big Bang, these “relic” neutrinos exist all through your complete universe, however they will’t hurt you. In actual fact, solely one in every of them is prone to calmly faucet an atom in your physique in your whole lifetime.
Most neutrinos produced – by objects similar to black holes – have way more power than the relic neutrinos floating via space. Whereas a lot rarer, these energetic neutrinos usually tend to crash into one thing and create a sign that physicists like me can detect. However to detect them, neutrino physicists have needed to construct very massive experiments.
IceCube, one such experiment, documented an particularly uncommon sort of significantly energetic astrophysical neutrino. These energetic neutrinos – generally known as tau neutrinos – typically masquerade as different, extra frequent sorts of neutrino. However for the primary time, my colleagues and I managed to detect them, pulling out a couple of from virtually 10 years of knowledge. We published our research within the peer-reviewed journal Bodily Evaluate Letters on April 11, 2024.
Their presence places researchers like me one step nearer to unraveling the thriller of how extremely energetic particles like astrophysical neutrinos are produced within the first place.
IceCube observatory
The IceCube Neutrino Observatory is the 800-pound gorilla of enormous neutrino experiments. It has about 5,000 sensors which have peered intently at a gigaton of ice beneath the South Pole for over a decade. When a neutrino collides with an atom within the ice, it produces a ball of sunshine that the sensors report.
IceCube has detected neutrinos created in a number of locations. These embody Earth’s atmosphere, the middle of the Milky Way galaxy and black holes in other galaxies many light-years away.
However the tau neutrino, one sort of significantly energetic neutrino, has eluded IceCube … till now.
Neutrino flavors
Neutrinos are available three different types, which physicists name flavors. Every taste leaves a definite imprint on a detector like IceCube.
When a neutrino bangs into one other particle, it normally produces a charged particle that corresponds with its taste. A muon neutrino produces a muon, an electron neutrino produces an electron, and a tau neutrino produces a tau.
Neutrinos with a muon taste have essentially the most distinctive signature, so my colleagues and I within the IceCube collaboration naturally looked for these first. The muon emitted from a muon neutrino collision will journey via a whole lot of meters of ice, making an extended observe of detectable gentle, earlier than it decays. This observe permits researchers to hint the neutrino’s origin.
Electron neutrinos
The group subsequent checked out electron neutrinos, whose interactions produce a roughly spherical ball of sunshine. The electron produced by an electron neutrino collision by no means decays. Plus, it bangs into each particle within the ice it comes close to. This interplay leaves an expanding ball of light in its wake earlier than the electron lastly involves relaxation.
For the reason that electron neutrino’s route could be very arduous to discern by eye, IceCube physicists utilized machine learning techniques to level again to the place the electron neutrinos may need been created. These methods make use of subtle computational sources and tune thousands and thousands of parameters to separate neutrino indicators from all recognized backgrounds.
Tau neutrinos
The third taste of neutrino, the tau neutrino, is the chameleon of the trio. One tau neutrino can seem as a observe of sunshine, whereas the subsequent can seem as a ball. The tau particle created within the collision travels for a tiny fraction of a second earlier than it decays. And when it does decay, it normally produces a ball of sunshine.
These tau neutrinos create two balls of light, one the place they initially bang into one thing and create a tau, and one the place the tau itself decays. More often than not, the tau particle decays after touring solely a really brief distance. Thus, the 2 balls of sunshine overlap a lot that they’re indistinguishable from a single ball.
However at increased energies, the emitted tau particle can journey tens of meters, leading to two balls of sunshine separate from each other. Physicists armed with these machine studying methods can see via this to search out the needle within the haystack.
Extracting these uncommon neutrinos
With these computational instruments, the group managed to extract seven robust candidate tau neutrinos from about 10 years of knowledge. These taus had increased energies than even essentially the most highly effective particle accelerators on Earth. And meaning they should be from astrophysical sources, similar to black holes.
This knowledge confirms IceCube’s earlier discovery of astrophysical neutrinos, and so they confirm a hint that IceCube beforehand picked up of astrophysical tau neutrinos.
These outcomes additionally counsel that even on the highest energies and over huge distances, neutrinos behave in much the same way as they do at decrease energies.
Particularly, the detection of astrophysical tau neutrinos confirms that energetic neutrinos from distant sources change flavor, or oscillate. Neutrinos at a lot decrease energies touring a lot shorter distances additionally oscillate in the identical manner.
As IceCube and different neutrino experiments collect extra knowledge, and scientists get higher at distinguishing the three neutrino flavors, researchers will finally be capable of guess how neutrinos that come from black holes are produced. We additionally need to discover out whether or not the space between Earth and these distant astrophysical neutrino accelerators treats particles differently depending on their mass.
There’ll at all times be fewer energetic tau neutrinos and their muon and electron cousins in contrast with the extra frequent neutrinos that come from the Large Bang. However there are sufficient on the market to assist scientists like me seek for essentially the most highly effective neutrino emitters within the universe and research the limitless space in between.
Doug Cowen, Professor of Physics and Professor of Astronomy and Astrophysics, Penn State
This text is republished from The Conversation beneath a Inventive Commons license. Learn the original article.
Backside line: Scientists have extracted seven robust tau neutrino candidates (a uncommon sort of neutrino) from about 10 years of knowledge from the IceCube observatory on the South Pole in Antarctica.
