How Are Neutrino Flavors Different ? Maybe There Is Only Vanilla . . .

Muon vs Electron Neutrino Decay Tracks
Credit: Duke U. Saturday Academy

Neutrinos are fundamental particles, more closely related to Electrons than Neutrons because they are not made up of smaller particles (Neutrons are made up of 3 Quarks).

Here are some odd things about Neutrinos.

1. All three flavors (types) of Neutrinos have zero electric charge making them beyond invisible; nearly impossible to detect. They are only affected by the Weak force and Gravity; both effects are extremely difficult to detect at the atomic scale.

What makes Neutrinos unique among particles is that they seem to change structure or “flavor” (called oscillation) . . . in very short distances. (Kind of like the Transformer toys – except instead of changing shape, Neutrinos seem to change mass ! – both up and down – which of course violates the bedrock principle of conservation of mass-energy.)

The only way to discern which “flavor” of a neutrino you’ve found is by which charged particles it creates when it does interact.

Neutrinos are named by the detectable (charged) particles they make in a decay process:

An “electron neutrino” makes an electron (an elementary particle with a negative charge) Mass < 2.2 eV

A “muon neutrino” makes a muon (A muon is an elementary particle similar to an electron, with a negative charge, but with a microsecond lifespan)       Mass < 170 keV

A “tau neutrino” makes a tau lepton (A tau lepton is an elementary particle similar to the electron, with a negative electric charge) Mass < 15.5 MeV

2. Mass / Energy Change ?

Unlike other subatomic particles, which have a constant “rest” mass-energy, Neutrinos can have different energies ranging from MeV to GeV (millions to billions of Electron Volts). (As much as 40 GeV)

3. How can an un-charged Neutrino have an anti-particle?

Since the only thing different about particles and their anti-particles is supposed to be their electric charge, and a neutrino is an elementary particle with zero charge – how can their anti-particle have a negative-zero charge?

Wikipedia : “Because antineutrinos and neutrinos are neutral particles it is possible that they are actually the same particle. Particles which have this property are known as Majorana particles.”

Unsatisfactory Answer: Anti-Neutrinos do not have a different charge (both are zero). However, they do have a different helicity (right-handed) or twist.

However, helicity is not used to determine anti-matter character for any other particles.

Interesting Hypothesis (by MIT theorist Frank Wilczek): When “opposite” Majorana particles interact – they annihilate.

Update Sept 28, 2011:

In the 1950s and 1960s, hundreds of strongly interacting particles were found. It later was decided they were just Quark composites. The “discovery” of Quarks (which  are inseparable from their host particle, and have never been observed) greatly simplified the Standard model. Could something similar be occurring now ?

Consider : All three flavors of Neutrino have the —

a) same charge (0),
b) same spin amount (1/2),
c) same helicity (left-handed),
d) same color charge (none),
e) same charge for daughter particles (negative),
f) apparently the same mass (tiny but undetermined), (however “If neutrinos have masses, then there is a spectrum of three or more neutrino mass eigenstates“)
g) and nearly identical “bubble trails.”

The only ways flavors are currently distinguished is, not directly but, by which particles they kick in a detector, and the shape of their “bubble trails.”

The problem is that Neutrino “flavor detectors” specialize in a specific Neutrino type so they can’t detect different flavors.

The only other way to tell flavors apart in a single detector is with “bubble trails” but the trails of each flavor are almost indistinguishable from each other; they require subjective judgment rather than objective measurement.

Hypothesis: With immense respect, admiration and appreciation for Neutrino flavor researchers, I propose that there is only one Neutrino. I suggest the different Neutrino “flavors” are just different effects of identical Neutrinos hitting different parts of an atom (Electrons, Quarks, Protons, Neutrons) at different angles (e.g. head on, same direction, sideways, glancing blow).

Lets try a thought experiment and pretend there is only one type of neutrino making it “flavorless.” (This has nothing to do with poor taste)

For example, perhaps an “electron neutrino” is detected when a “plain Vanilla” Neutrino hits an Electron. Then a “muon neutrino” is detected when a Vanilla Neutrino hits an Up Quark, and a “tau neutrino” is detected when a Vanilla Neutrino hits a Down Quark.

A FermiLab Neutrino Event
Credit:Fermilab

This hypothesis could help explain the unique oscillation itself, and the excess oscillations found by the MiniBooNE experiment and Los Alamos’ Liquid Scintillator Neutrino Detector which suggest yet a fourth flavor – a “Sterile” Neutrino. This flavor is even more invisible. It is apparently not even affected by the Weak force – only by Gravity.

It could also help explain the puzzle of a particle with energy / mass varying over several magnitudes: Different strike angles give different energy results. For example, since electrons orbiting atoms are already moving at near the speed of light — a head-on strike should produce a very different result than a “rear-end” strike. (That’s why we use “colliders” where nearly light speed particles hit each other head-on, rather than race protons in the same direction around until one slowly catches up with another.)

There’s one last thing – the Standard (Particle) Model predicts that neutrinos are massless. However, recent neutrinos apparently oscillating undermines the Standard particle Model by implying that Neutrinos should have a mass. It would be at least half a million times smaller than an Electron, but not massless.

Experimental Test

The two main experiments I can propose to test this hypothesis must wait until we can engineer a “Neutrino prism” or a genuine “Neutrino spectrometer,” or until we can reliably aim a stream of Neutrinos at a specific Neutron or Proton. While neither is intrinsically impossible, we are likely at best decades away from either engineering feat.

On the other hand, since there is nothing that objectively distinguishes one flavor Neutrino from another, perhaps the responsibility (Burden of Proof) is still on the claims that there are flavors — to provide an objective way distinguish them.

 “In science, the burden of proof falls upon the claimant; and the more extraordinary a claim, the heavier is the burden of proof demanded. The true skeptic takes an agnostic position, one that says the claim is not proved rather than disproved. He asserts that the claimant has not borne the burden of proof and that science must continue to build its cognitive map of reality without incorporating the extraordinary claim as a new “fact.” –  “On Pseudo-Skepticism”, Marcello Truzzi, Zetetic Scholar, 12/13, pp3-4, 1987 :

However, there is yet another possibility. One Neutrino facet generally unmentioned is how Neutrinos are affected by gravity. Since they travel darn close to Light Speed, if Relativity still works, perhaps their mass could help with an experiment, rather than be an annoyance.

For example, we could put a satellite in orbit around our Moon and shoot Neutrinos back at Earth and see if Neutrinos that graze the Moon’s surface travel as straight a path as those shot through the Moon’s center.

Space-based Neutrinos are extremely difficult to detect because every square centimeter on Earth (facing the Sun) encounters some 65 billion solar neutrinos per second.

Update Feb 2013: Using Polarizing filters we can make light appear and disappear due to changing alignment with its “flight” path. Could it be that Neutrino oscillation changes mass by changing alignment? Is it possible that mass disappears under certain alignments (i.e. polarization) of a Neutrino?

With the new excitement in apparently Superluminal Neutrinos engendered by the OPERA experiment, perhaps there will be more resources put towards such research. And who knows – maybe Neutrino’s odd changing mass “in flight” will point us to an understanding of what mass is.

Update 2015: The 2015 Nobel Physics Prize was just awarded to researchers “for the discovery of neutrino oscillations, which shows that neutrinos have mass.”

This means my hypothesis presented by this article must be wrong ;-)

Note: One thing to keep in mind is that the experiments claiming a neutrino changes (oscillates) do not follow a single neutrino and detect if it is changing from one type to another. Instead the researchers detect a load of neutrinos and use statistics to interpret that some neutrinos are changing.

References:

OPERA = Oscillation Project with Emulsion-tRacking Apparatus (“Finish Line”)

Neutrino Physics at Duke University

Fermi National Accelerator Laboratory