Chameleon-Like Behavior of Neutrino Confirmed

Anonymous Apcoheur writes "Scientists from CERN and INFN of the OPERA Collaboration have announced the first direct observation of a muon neutrino turning into a tau neutrino. 'The OPERA result follows seven years of preparation and over three years of beam provided by CERN. During that time, billions of billions of muon-neutrinos have been sent from CERN to Gran Sasso, taking just 2.4 milliseconds to make the trip. The rarity of neutrino oscillation, coupled with the fact that neutrinos interact very weakly with matter, makes this kind of experiment extremely subtle to conduct. ... While closing a chapter on understanding the nature of neutrinos, the observation of neutrino oscillations is strong evidence for new physics. The Standard Model of fundamental particles posits no mass for the neutrino. For them to be able to oscillate, however, they must have mass.'"

Comments

Re:Who would have guessed

[NotQuiteReal]

Nobody every buys the Standard Model. If you have the money you get the Luxury Model. Otherwise, most folks just aim for the middle and get the Sports model.

Excited!

[SpeedyDX]

Reading TFS made me very excited about the potential fundamental developments in physics. Except I don't know a thing about physics, so I'm really not sure what I'm excited about. All these words like muon, tau, and neutrino have little place in my everyday life, but they sound so interesting!

This is what the Average American must feel like when they hear stories about Web x.0 laden with the latest buzzwords on CNN. I can finally relate!

Re:Excited!

[$RANDOMLUSER]

...we need some Slashdotter to come up with a car analogy to help us non-physicists out.

Glad to oblige.

Imagine a highway. All the north-bound cars are WHITE Toyota Camrys, and all the south-bound cars are BLACK Toyota Camrys. All the cars are moving very very very fast. At a certain point in the road, workers open gates that cause the two streams of traffic to plow into each other, head on. At the crash site, common sense would tell you that pieces of Toyota Camrys would come flying out, but instead, complete vehicles of other makes and models (Honda Civics and Nissan Sentras, many others, including vehicles larger than two Camrys, like Peterbilt 18-wheelers) appear instead. After a few seconds, some of these vehicles break apart, and become other vehicles, say a Peterbilt breaks apart and becomes a Ford F-150 and two Harley Davidson motorcycles. Particle physicists make a living by crashing different streams of vehicles into each other and observing the new vehicles that come out. They've put together a list of these, like "Peterbuilt --> Ford F-150 + 2(Harley Davidson Motorcycles)". They call this list the Standard Model. This new experiment shows that sometimes, after a while, one of the Harleys suddenly changes models, say from a Fat Boy to an Electra Glide.

Hope this helps.

Chameleon-Like Behavior?

[Randle_Revar]

I don't see how changing from one thing into another is "chameleon-like behavior". I have never heard of a chameleon turning into a skink, or anything else for that matter

Re:What if...

[Steve Max]

You'd need a pretty complex theory to get non-mass oscillations to match all the data we got over the past 12 years, which is very compatible with a three-state, mass-driven oscillation scenario. Besides, you'd have to explain more than what the current "new standard model" (the SM with added neutrino masses) does if you want your theory to be accepted. If two theories explain the same data equally well, the simplest is more likely.

Re:How in the universe?

[rogeriomgatto]

That's how they managed to escape the priests... They avoid mass.

Re:How in the universe?

[hoytak]

Neutrinos only interact through the weak forces, which require them to be extremely close to other particles with which they interact. Such interactions also require the neutrino to have a lot of energy, since the force-carrying particles are quite massive. This is why all these experiments use neutrinos generated by very energetic reactions (accelerators, the sun, cosmic rays, etc.).

When I worked with BooNE, an experiment researching neutrino osculations, our detector was a 40 ft tank lined filled with clear, food-grade mineral oil and lined with photo tubes capable of detecting a few photons. The neutrinos were generated by bursts of protons crashing into a special block (I don't remember the material), and the byproducts at the given energy levels would be one type of neutrino. The interactions from different types of neutrinos would have different decays, which produced different signature rings of photons on the walls of the detector. In generating 10^9 + neutrinos, we only expected a handful of interactions.

Gravity is also on the table, but it's impossible to measure neutrinos based on that.

Re:What if...

[BitterOak]

That would be pretty amazing as it would violate the Special Theory of Relativity, one of the most tested theories of all time. The problem is, according to Special Relativity, massless particles move at the speed of light, and time does not advance for them. (If you could build a massless clock, its hands would never move.) Oscillations require a time scale. There is a time period of oscillation, or rather the probabilities of being found in a specific state (mu vs. tau, for instance) oscillate with time. Since time stands still for massless particles, this can't happen.

Re:How in the universe?

[BitterOak]

How could something have mass and so weakly interact with normal matter?

Neutrinos are thought to have a very small mass. So exceedingly small that they barely interact with anything (they also have no charge, so they are even less likely to interact).

The fact that they barely interact with anything has nothing to do with the fact that they are nearly massless. Photons are massless and they interact with anything that carries an electric charge. Electrons are much lighter than muons, but they are just as likely to interact with something. The only force that gets weaker as the mass goes down is gravity, which is by far the weakest of the fundamental forces.

Re:How in the universe?

[Snowhare]

It isn't their mass that makes them so unlikely to interact with ordinary matter. It is because they don't interact via the Electromagnetic or Strong Nuclear forces (at least not at the energies we are discussing here). Because we can't use gravity to directly detect them (or any other elementary particle) because of its incredible weakness, that leaves only the Weak Nuclear force, which is *extremely* short range. That short range means that a neutrino must pass *very* close to an electron or a quark to have any chance what-so-ever of interacting: Something like 10 to the minus 16th power meters. For comparison, a hydrogen atom has a diameter of around 10 to the minus 10th meters - or a million times larger.

A single *proton* has a diameter of around 10 to the minus 15th meters - or still 10 times larger than the distance in question.

So hundreds of neutrinos could pass directly through the very nucleus of an atom and *still* not interact with anything. And that is matter with a density more than a trillion times as dense as anything in your ordinary experience.

To neutrinos, other matter barely exists at all.

Re:What if...

[Steve Max]

The point is that, if two different theories have the exact same predictions, they are for all intents and purposes the same theory, and describe the same universe. If that is the case, why would you spend more time teaching and learning the more complex one, when a simple explanation is enough and (by definition, since they have the same predictions) you can't tell which one is correct?

Of course, if the new theory offers a good explanation to current data, but has a different prediction than the standard model in other, still-non-tested scenarios, the theory is more interesting. You can test it at the new scenario, and you'll be able to tell them apart. This is why* we study, for example, supersymmetry and extra dimensions theories: they behave just like the standard model where we have tested it, but can be different in other cases such as the LHC.

* = of course there are other motivations to develop the theories, but they are taken seriously because they are compatible with the SM and are testable. A theory whose predictions were exactly the same as the SM for every case wouldn't be worth studying, simply because you'd never be able to see if it is right.

Re:What if...

[BitterOak]

That's the way I've always understood the mass/oscillation connection too. But then I thought... wait... don't photons oscillate too? They're just coherent oscillations of the EM field; oscillating back and forth between electric and transverse magnetic in free space. If there's something different about neutrino oscillation which makes it necessary for the neutrino to travel at sublight, what is it specifically?

The situation you describe with the EM field is an example of wave-particle duality. Light can behave like both a wave and a particle, but it doesn't make sense to analyze it both ways at the same time. As a wave, it does manifest itself as oscillating electric and magnetic fields and as a particle, it manifests itself as a photon, which doesn't change into a different type of particle. (There's no such thing as an "electric photon" and a "magnetic photon".)

Neutrinos, too, are described quantum mechanically by wavefunctions, and these wavefunctions have frequencies associated with them, related to the energy of the particle. But these have nothing to do with the oscillation frequencies described here, in which a neutrino of one flavor (eg. mu) can change into a different flavor (eg. tau). Quantum mechanically speaking, we say the mass eigenstates of the neutrino (states of definite mass) don't coincide with the weak eigenstates (states of definite flavor: i.e. e, mu, or tau). Without mass, there would be no distinct mass eigenstates at all, and so mixing of the weak eigenstates would not occur as the neutrino propagates through free space.