Flavors of neutrinos

The fact that neutrinos exist in three flavors is maybe the most crucial thing to know about them.

muon neutrino (ve) – electron neutrino (νμ) – Neutrino tau (ντ)

Each type of neutrino is regarded as a fundamental particle, or one of the fundamental building components of our universe that cannot be broken down further. They are related to three fundamental particles with similar names: the electron, muon, and tau. When a neutrino interacts (finally! ), its partner particle frequently appears. This allows scientists to figure out what kind of neutrino the particle was before it collided. Scientists never see the neutrino; instead, they see the additional particles that form when a neutrino interacts with another particle in a detector.

Neutrinos are unusual particles, and scientists were shocked to discover that their flavor changes as they move. Imagine buying a container of chocolate ice cream, driving home, and opening it to discover it was vanilla! So you put a scoop of vanilla in your bowl and walk into another room to eat it, only to discover it has turned strawberry. With neutrinos, this is exactly what happens. A particle may begin as an electron neutrino, but as it travels, it transforms into a muon neutrino or a tau neutrino, changing flavors. Scientists can learn a lot about neutrinos by studying how they change as they travel.

Neutrinos were first proposed by Wolfgang Pauli in 1930 as a way to balance the math (and the energy) in a phenomenon known as beta decay, which occurs in the nucleus of an atom. A radioactive decay that emitted a proton (positively charged particle) and a so-called “beta particle” was observed by scientists (an electron). But, due to the mandates of many laws, such as conservation of momentum, energy, and angular momentum, or spin, there had to be an invisible particle that played a role. Originally known as a “neutron,” the neutrino is a small neutral particle that carries away some of the energy, momentum, and spin of other particles.

Frederick Reines and Clyde Cowan discovered neutrinos experimentally in a reactor experiment in 1956. Antineutrinos from a nuclear reactor collided with protons, producing a neutron and a type of antimatter known as a positron through a process known as “inverse beta decay” (a positively charged version of an electron). This antimatter was swiftly destroyed by conventional matter, resulting in gamma rays. The electron antineutrino had been discovered—and associated with its eponymous particle, the electron—despite the fact that Reines and Cowan were unaware that neutrinos might have antiparticles or flavors.

A few years later, a group of scientists at Brookhaven Laboratory utilized a beam of protons to create a shower of particles that decay into muons (heavy cousins of electrons) and neutrinos, similar to “beta decay.” In contrast to neutrinos produced in reactors, which make antielectrons when they interact, neutrinos produced in the accelerator produced muons when they interacted. The neutrinos have an obvious relationship with their charged counterparts. Muon neutrinos had been discovered.

Scientists had finally identified the three neutrino flavors and discovered that neutrinos could alter their flavors as they traveled. Neutrinos were considered to be massless from the beginning by scientists. Neutrinos, on the other hand, needed to have mass in order to change flavor. The discovery of non-zero neutrino mass is still considered one of the most important examples of physics outside the Standard Model, as well as one of the few places where the model fails. Scientists are particularly interested in resolving neutrino mass puzzles, such as how much the tiny particles weigh and how the three masses interact.

Dmitri Mendeleev sought to order atoms by their weight when he was trying to make sense of them in 1869. When the elements were grouped into the periodic table, it became evident that some of them interacted chemically in a similar way, despite their vastly differing masses. The underlying structure was then understood by Mendeleev and others: different elements’ atoms were actually made up of the same underlying components in varied configurations. The smaller bits are now known to be protons, neutrons, and electrons.

Murray Gell-Mann and Yuval Ne’eman achieved the same technique almost 100 years later, organizing particles detected in cosmic rays and accelerators by their masses. Scientists discovered that even though certain particles had very different masses, they may respond in similar ways. Gell-Mann and George Zweig proposed quarks as the underlying components of these particles (protons, neutrons, and their heavier counterparts), which we now know as fundamental building blocks of matter.

The Standard Model is the physics version of the periodic table, but scientists aren’t sure if there are smaller underlying particles. What they do know is that there appear to be three generations of quarks, as well as three generations of charged leptons, which include electron-like particles and neutrinos. It could just be a coincidence that both quarks and leptons have three generations, but quark weak interactions resemble lepton weak interactions: a heavy quark can decay into a lighter quark, and a heavy lepton can decay into a lighter lepton.

In 1897, electrons were discovered, and in 1936, the muon, their heavier relative, was identified in cosmic rays. The tau, the heaviest form, was discovered in 1975.

The leptons, like quarks, come in a variety of flavors. The flavor of neutrinos, on the other hand, is not determined by their mass. Instead, the flavor of a neutrino is decided by how heavy its charged lepton partner is at the time of its creation (or from how heavy the charged lepton is that gets produced when the neutrino interacts).

Quarks and leptons are thought to be related due to their weak force relationship, according to scientists. A particle made up entirely of the lightest quarks (such as an up and an antidown quark) can decay into a muon and a muon-flavored neutrino, for example. A particle made up of one or more heavier quarks, on the other hand, can decay into lighter quarks or leptons (or into both).

Flavor physics is the scientific study of these transitions between quarks or neutrinos. However, referring to them both by the same name fails to convey how dissimilar the probabilities are. While there is a lot of mixing between neutrino flavors, if a quark is lighter, it will generally transform into another quark from the same family. Only a few percent of the time will it convert to a one-generation away quark, and only one out of a thousand times will it transition to a two-generation away quark.