What do neutrinos look like

Each kind of source produces different neutrino flavors at different energies. By carefully counting neutrinos of each flavor at various distances from these sources, scientists have made two remarkable discoveries about neutrinos. First, they discovered that neutrinos of the three different types morph into each other as they travel through space!

In other words, the messages the neutrinos carry change as they fly. Second, they discovered that neutrinos have a very tiny mass! The scientists had designed their detector to receive only one type of neutrino—electron neutrinos generated in the core of the sun.

They could calculate exactly how many electron neutrinos should be detected. But only about one-third of the expected electron neutrinos showed up in the detector. Through follow-up experiments, scientists eventually learned the reason behind this mystery: Some of the electron neutrinos had morphed into one of the other two flavors muon or tau while on their journey from the sun. Because the detector was blind to those other two flavors, they appeared to be missing!

It had to be tested by other experiments. Other experiments used atmospheric neutrinos, reactor neutrinos, and accelerator neutrinos. The new DUNE experiment in the United States and the Hyper-Kamiokande experiment in Japan will reveal more details about the shape-shifting behavior of neutrinos and antineutrinos.

If scientists find a difference between how neutrinos and antineutrinos transform, it might solve one of the most important mysteries in the universe: why the universe is made only of matter and not antimatter. Scientists think both matter and antimatter were created in equal amounts in the Big Bang.

Equal amounts of these two opposites should have destroyed one another leaving only light! So, the existence of only matter today is evidence that there was a small excess of matter.

It is possible that the difference between neutrinos and antineutrinos caused this small excess as the universe expanded and cooled. If this is true, we have neutrinos to thank for the universe we have today, filled with all the visible stuff around us, including rocks, plants, animals, and people!

In the sun, hydrogen nuclei protons combine to form helium nuclei and release energy—heat and sunlight. This process of breaking apart is called radioactive decay. These identical but oppositely charged particles are antimatter or antiparticles. For example, the antimatter counterpart of a muon negatively charged is an antimuon positively charged. Neutrinos do not have charge, but they also have antiparticles; understanding the nature of these antineutrinos is one of the most important mysteries in physics.

The three fundamental negatively charged particles are the electron, the muon, and the tau particle. They are identical in every way except that the muon is times heavier than the electron, and the tau is 3, times heavier.

It is good for detecting neutrinos because ionization lingers long enough to be detected. The results are positively charged ions and free electrons.

The rock around the detector blocks any radiation not powerful enough to penetrate beneath the Earth; because neutrinos are so "slippery", they can pass through the rock and reach the detector device. Neutrinos are valuable to astronomers precisely because they are so evasive.

Since even large thicknesses of matter don't have much effect, neutrinos can flow right through things which distort or block other types of radiation. For example, our Sun is a ball of hot gases, 1,, kilometres , miles in diameter. Nuclear fusion reactions at the Sun's core heat these gases, producing vast quantities of energy. We would like to know the details of what's going on inside the Sun's core, but the gaseous layers in the way block our view.

The gas atoms scatter light so well that a single photon, the basic particle of light, takes roughly fifty thousand years to reach the Sun's surface. Photons leave the core, hit nearby atoms, bounce off them, hit other atoms, and spend centuries doing more and more of the same, until they manage to leak out in the thinner regions near the surface. All that scattering and jostling obscures the details of the interior, just like a bright city skyline looks vague and indistinct when observed through a thick fog.

Neutrinos avoid this problem, because they don't like to interact with the Sun's atoms. Once nuclear reactions in the core produce neutrinos, they can radiate away and rapidly escape the Sun. Neutrino detectors, then, can tell us what happens deep within the solar core, because they bring us information directly from the source. In the city analogy's terms, they zip through the fog and reveal the metropolis behind it.

The neutrino entered physics as the brainchild of Wolfgang Pauli Pauli was trying to explain a puzzling feature of beta decay, a type of nuclear reaction that frequently occurs in unstable heavy elements. In beta decay, a neutron within the atomic nucleus breaks down and turns into a proton, releasing an electron which flies away from the atom.

Measurements showed that the electron's energy varied: sometimes it barely crept out of the nucleus's pull, and sometimes it shot away at high speed. Physicists could explain the high-energy case fairly easily: the electron simply carried the maximum energy the reaction could produce.

What about the lower-energy cases, Pauli wondered. A basic principle, the Conservation of Energy, says that energy cannot vanish from existence. In cases where that appears to happen, it is in fact being transformed into a less obvious form. To a physicist, watching energy vanish from a situation is like how many people feel watching money disappear from their bank account.

The most popular theory proposes a completely new mass mechanism at play that is not within the Standard Model, one which introduces an entirely new particle. It could be something that looks like a Higgs boson or a kind of electron-like particle. It could even be multiple particles whose collected effect gives neutrinos their mass.

One of the most popular forms of this theory is the Seesaw Mechanism, which accounts for the teeny-tiny size of the neutrino. The first and most important question to answer is: Are neutrinos Majorana fermions? In this process, a neutron inside an isotope, in this case a germanium isotope, decays and spits out an electron and neutrino.

Scientists are looking for neutrinoless double beta decay, in which the nucleus seems to emit only two electrons and no neutrinos because the neutrinos have paired Majorana-style and been annihilated. Observing double beta decay is extremely rare. Neutrinoless double beta decay—if it occurs—would be even rarer. Questions like: Why is there more matter in the universe than antimatter?

Why is the expansion of the universe accelerating? Where does dark matter come from? Scientists on an experiment at the Large Hadron Collider see massive W particles emerging from collisions with electromagnetic fields. How can this happen? Nearly 75 years after the puzzling first detection of the kaon, scientists are still looking to the particle for hints of physics beyond their current understanding. Scientists know the Higgs boson interacts with extremely massive particles.