The Greatest Neutrino Discoveries in the Universe

The Neutrino Factory

It’s not the fanciest of names, but it’s the name that stuck. In the 1990s, physicists theorized that a neutrino factory could be used to produce large numbers of neutrinos to study their properties. A particle accelerator would produce beams of protons and electrons, which would collide with a target and produce pions (a type of meson). The pions decay into muons and muon-neutrinos when they reach rest after being accelerated by a magnetic field. These muon-neuts then enter an underground laboratory where detectors observe them as they pass through the detector material. This is referred to as “oscillations” between states—each time the muon decays into another particle, its state changes from one type into another (muon-neutrino -> electron+muon). The researchers can use this method for studying these oscillations in much greater detail than before: knowing how many neutrinos are produced at each stage gives them more information about what types there might be!

Supernova 1987A

The first neutrinos to be detected in 1987 were produced by a Type II supernova, SN 1987A. This was a gigantic stellar explosion that created one of the most famous images of all time: The "Pillars of Creation" located in the Eagle Nebula. It was discovered by NASA's Hubble Space Telescope as a result of its outburst and has since been extensively studied in order to understand how supernovae occur, what causes them, and how they affect their surrounding environments.

In addition to being the first neutrino observation ever made, this discovery offered evidence for Neutrino Oscillations—a phenomenon where certain types of neutrinos are actually able to transform into other types over time—which led scientists down another rabbit hole with further implications on particle physics research.

Neutrino Oscillations

Neutrinos are quantum mechanical particles that can take on three different flavors: electron, muon and tau. Each flavor of neutrino has a corresponding antineutrino, with the same mass but opposite charge. To date, all of the evidence indicates that this system is symmetric—that it doesn’t matter which flavor of neutrino you choose to examine; their properties are identical to their anti-particles.

This is a very important property because it means that you can use one type of neutrino (say an electron) as your “clock” for measuring time and then compare it with its corresponding antineutrino (the positron). If everything were symmetric, then these two clocks would read exactly equal amounts over time through Einstein's famous theory of special relativity. However, if they didn't read equal amounts after going some distance away from each other due to differences in mass or energy between them (or whatever), then we could measure those differences in clocks!

This was exactly what happened when scientists first observed oscillations between electron neutrinos and muon antineutrinos at SuperKamiokande in 1998. They observed that there were fewer electrons than expected even though there should have been just as many electrons left behind as positrons if nothing changed while they moved away from each other. They also saw more muons than expected by comparing them against their original source which also contained no positrons!

Atmospheric Neutrinos

The first detection of atmospheric neutrinos came in 1956, and was the result of an accident. A cosmic ray proton struck a nitrogen nucleus in the atmosphere, creating a muon and converting it into an electron and its antimatter equivalent called a positron. The positron quickly annihilated with an electron in the atmosphere to create two photons (gamma rays).

The next important discovery was made by Kamiokande II, which detected solar oscillations in 1989. The experiment was located deep underground and consisted of a tank filled with 50 million tons of water. When gamma rays produced by neutrinos or collisions of other particles entered the tank, they would interact with protons or electrons that were already present in all that water and produce Cerenkov radiation—visible light emanating from glowing particles moving faster than light speed through water.

Atmospheric Neutrinos and the Discovery of Muon Neutrinos

In 1987, atmospheric neutrinos were discovered by the Kamiokande detector. This detector was located deep underground in order to eliminate as much background radiation as possible. Muon neutrino masses and oscillations were measured because Kamiokande was sensitive enough to detect these particles even though they're weakly interacting and have very small cross sections for interaction with matter (making them difficult to detect).

In an attempt to increase sensitivity, researchers built larger detectors that could look for supernova explosions or other high-energy sources in addition to cosmic rays. These experiments found no evidence of solar neutrinos, so eventually a theory called "neutrino oscillations" was developed that explains how this can be possible: when a muon neutrino travels from the sun through Earth's atmosphere, it transforms into an electron neutrino along the way!

Particle Mass Determination

It's well established that neutrinos have mass, but the exact value of their mass is still a mystery. This is due to the fact that neutrinos interact only very rarely with other particles, making them difficult to observe and measure.

In order to make these measurements, scientists look at how much energy a neutrino has when it decays into an electron or muon (a type of charged particle). A heavier neutrino will decay with more energy than a lighter one; because we know how much energy electrons and muons have in theory, we can use this information to figure out what kind of neutrino was originally produced—this is called "particle identification."


SNO, the Sudbury Neutrino Observatory (SNO) is a neutrino observatory located 2000 m underground in Vale's Creighton Mine in Sudbury, Ontario, Canada. The detector was designed to detect solar neutrinos via their interactions with a large tank of heavy water. With this detector we were able to show that neutrinos have mass and that not all of them come from the sun.

We are starting to finally harness this elusive particle.

As we start to learn more about neutrinos, we are beginning to harness them. Neutrinos could be used in detectors for nuclear weapons or hidden bombs because they can pass through most solid matter and easily find the explosives. They could also be used as a power source for a spacecraft, but this has not yet been explored in detail.

One of the biggest discoveries made by studying these particles is that they have mass! This was not known until 1998 when two experiments found evidence that neutrinos do indeed have mass. This means that there are more than three types of fundamental particles making up our universe—meaning the Standard Model of Particle Physics may need some tweaking!

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