After a recently published article in the science journal Nature, particle physicists have been barking about the dog neutrino. Timing Glitches’ claim opens the door to let new and never-before hypothesized flavors of neutrinos into the subatomic particle zoo.

What Did We Know About Neutrinos?

What do we know about everything? Particle physicists have come up with the Standard Model to explain the make-up of our Universe. Neutrinos are a small part of this model, even smaller than atoms. The Standard Model includes:

• quarks – Neutrons and protons in the atomic nucleus are made-up of different combinations of quarks.
• leptons – Electrons are one kind of lepton which have mass and a charge. Neutrinos are a different kind of lepton in themselves, differing from electrons in that they have no electrical charge.
• force-carriers – Instead of making-up matter itself, the exchange of these particles is responsible for the physical forces between matter. One popular example is the saught-after Higg’s Boson as the force-carrier for the gravitational force.

Wolfgang Pauli first imagined the existence of the neutrino in 1930 to explain radioactive beta decay (this is caused by another one of the forces, the weak nuclear force) in a way that was compatible with physics’ laws of conservation. Pauli’s postulated particle had to be chargeless and massless or nearly massless. Enrico Fermi named these particles “neutrinos,” which diminuitively means “little neutral ones” in Italian.

Neutrinos were purely theoretical until 1956 when they were first detected coming from a nuclear reactor in the famous Cowan-Reines experiment. Another effort aimed at counting and characterizing neutrinos coming from the H-He fusion reactions taking place within our Sun (solar neutrinos) was the Homestake experiment, which ran from 1970-1994.

These later experiments counted the number of neutrinos coming from our Sun, but they found a serious discrepancy. Two-thirds the number of neutrinos predicted by the Standard Model theory at the time were missing! Scientists went back to the drawing boards to refine the Standard Model, and explained this dilemma by neutrino oscillation. In short, neutrinos must come in various flavors and be able to change this flavor in-flight (two-thirds of the neutrinos have therefore changed into a different “kind” of neutrino from the expected electron neutrino). Three flavors of neutrino were named in parallel to
the three flavors of leptons:

• electron neutrino – The originally-envisaged neutrino that was associated with electrons.
• muon neutrino – First theorized as the “neutretto,” the muon neutrino was later discovered by the Two-Neutrino Experiment in which a short-lived, energetic muon (a negatively-charged lepton heavier than an electron) was detected after the neutrino’s interaction with an atomic nucleus.
• tau neutrino – Discovered by the DONUT Experiment at Fermilab, a tau neutrino interacted with an iron atom’s nucleus to produce a tau lepton.

There is certainly more to say about quarks, leptons and neutrinos than I can possibly write here, so interested readers are encouraged to consult the following two resources. Young people can check-out the Particle Adventure, while college students may find greater detail in the HyperPhysics tutorials.

Tip For Remembering 3 Neutrino Flavors

A convenient mnemonic for remembering these three flavors of neutrinos is to think of paramedics in an ambulance. Ambulances have the right-of-way, allowing them to cruise through traffic in an emergency like neutrinos can pass through matter undisturbed. The paramedic in the ambulance is called an EMT (as in Emergency Medical Technician, or in this case: Electron, Muon, Tau). Remembering this should bring to mind the 3 flavors of neutrinos.

A Zoo of Neutrinos?

This was the world view in particle physics before the Glitches revelation turned heads on Twitter, amid some dogged experiments which had taken place last year. There was ongoing skepticism over anomalous measurements of neutrinos going faster-than-light, that universal speed limit which Albert Einstein held as inviolate. Many critics of
these experiments suspected something must be wrong, and discrepancies have since been found in synchronizing the various clocks used in the OPERA experiment after closer scrutiny. Neutrinos do not go faster than light.

But what was even more unexpected by everybody in the midst of this controversy was the “Timing Glitches Dog Neutrino Claim” headline. It might be that Glitches’ claim found a richness in the neutrino flavors greater than what the Standard Model presently suggests. Conventional thinking holds that a fourth neutrino, were it to exist, must be tied to a fourth generation of (heavier-yet) leptons. Bucking this wisdom, the “dog” neutrino may better be described by how it sounds, rather than its relationship to a corresponding high-energy lepton with charge.

Detections of dog neutrinos could be observed by carefully monitoring an individual neutrino’s flavor oscillations over femtosecond time periods. When these oscillations have been slowed to the point at which they have an audible sound matching the waveform of a dog’s bark (woof!), the aptly-named dog neutrino can be resolved.

While thus far only the “dog neutrino” has been seen mentioned in the pages of a scientific journal, particle physicists may soon be purring about the possibility of a counterpart that effectively cancels a dog neutrino, the elusive (and not-yet-reported) “cat” neutrino.

No official naming has yet been determined for this theoretical flavor of neutrino (what I am calling the “cat” neutrino), but it seems reasonable to call the dog neutrino’s counterpart a cat neutrino, don’t you think? Admittedly, the likelihood of this neutrino’s flavor oscillations sounding like a cat’s meow would be far-fetched. More likely would be that the waveform of this hypothetical cat neutrino would be the inverse of the dog neutrino. This would support one explanation for the dearth of dog and cat neutrinos seen in nature: their propensity to annihilate each other almost instantaneously.

On the Tail of the Cat Neutrino

As with each prior generation of subatomic particles, today’s particle physicists need innovative new detection techniques, more powerful particle accelerators and test equipment to find these short-lived, chargeless, nearly massless neutrinos and their tell-tale oscillations. The dog neutrino tosses the scientific community a bone that hints at a much more diverse spectrum of massless particles if only we pay attention—including perhaps—the elusive cat neutrino.

Happy April 1st everyone.