Slashdot Mirror
Fermilab Confirms Evidence of 4th Flavor Neutrino
eldavojohn writes "We've only had evidence for three kinds of neutrinos so far, but a recent test at Fermilab involving an antineutrino beam has reinforced a Michigan researcher's earlier experiment suggesting a fourth flavor. What's really odd about this is that a prior neutrino test (carried out as part of project MiniBooNE) did not result in indications of such strange oscillations. According to the researcher, 'The simplest explanation involves adding new neutrino-like particles, or sterile neutrinos, which do not have the normal weak interactions.' But this could also be an unknown or misunderstood effect. A Los Alamos National Laboratory scientist added that an explanation of this strange anomaly could result in understanding 'matter asymmetry of the universe, or why the universe is primarily composed of matter, rather than antimatter.' The results are published in the Physical Review Letters."
4th flavor of neutrino; "I hope it's grape", that's just good comedy right there.
Yes, but you're never going to get one to hit your taste buds.
I swear to God...I swear to God! That is NOT how you treat your human!
No, no, no the neutrino flavors follow the same pattern as basic emotions: Happy, sad, approving, disapproving and umami. Umami is a relatively recently discovered emotion. It feels like broth.
Some of my favourite people are from th US; Vonnegut, Chomsky, Bill Hicks.
Billions of them pass through your taste buds every second. The problem is getting them to interact with your taste buds.
Technoli
Now, IANAPP (particle physicist), but I thought one of the things discrediting Heim Theory was the prediction of more than 3 neutrinos. What does the presence of a fourth neutrino mean for other predictions made by the current model? Does this mean that Heim's predictions may have more credence?
I think the bigger issues would be the wildly incorrect values for extremely well-known parameters (90ish sigma away from the measured mass of the proton, for instance) and the prediction of a "neutral electron" at a mass that should make it appear in pretty much every particle physics experiment EVAR.
CERN != Fermilab
No folly is more costly than the folly of intolerant idealism. - Winston Churchill
Those guys in white coats all look alike to me.
What has been found is an excess of certain events (namely anti-muon-neutrino to anti-electron-neutrino oscillations), where "excess" is defined relative to the current best-established model. So what this experiment (if correct) shows, is that the current model is not good enough.
From the PRL paper:
The source of the excess remains unexplained, although several hypotheses have been put forward
One of those hypotheses is additional neutrino flavours, but this finding is not evidence for that.
Billions of them pass through your taste buds every second. The problem is getting them to interact with your taste buds.
So, they have no calories!
I'm on the neutrino diet plan now. I just need to get booked on "The View" and I'll be rich!
Move over Atkins, here comes the Neutrino Diet!
RIP America
July 4, 1776 - September 11, 2001
I can't speak for people from a hypothetical universe and about what their naming conventions would be, but I can tell you that, given the known laws, the "anti-matter" universe would behave in exactly the same way as ours does.
No, this isn't true (unless time also runs backwards in the anti-matter universe).
Neutral Kaon decay violates CP - You can distinguish K0 decay in our universe from the anti-K0 decay in an antimatter universe.
It is conjectured that CPT symmetry does hold (therefore CP violation implies T violation)
http://en.wikipedia.org/wiki/CP_violation
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
Next up: "When Cantor Sets collide"
Well, IAAFPP (I Am A Former Particle Physicist, now no longer active in the field), and you have to be careful what you mean by "neutrino". In the Standard Model, neutrinos are partners to the charged leptons: electron, muon, or tau lepton. By "partner to", I mean connected (in a sense) by the weak force, which is the only non-gravitational force that acts on them (being neutral, they are immune to the electromagnetic force, and being leptons, they don't feel the strong force). Neutrinos are also very light, having near-zero mass.
This is what the Standard Model calls a neutrino. And there are, in fact, only 3 kinds. This was shown pretty convincingly by LEP at CERN. And it's also enough to discredit Heim's Theory (which no one really took seriously in the first place).
What this story is suggesting is that there may be a different kind of neutrino -- a so-called "sterile neutrino" -- that doesn't even feel the weak force. This isn't part of the Standard Model, but it is possible in certain extensions of the SM. This kind of neutrino doesn't act the same way as the SM neutrinos; it's a different beast, and comes about through a different part of the mathematics.
Since you are a /former) particle physicist, maybe you can explain me why it's not considered entirely natural that there are neutrinos which don't interact with the weak force. My consideration is the following: For each particle except the neutrino there are left-handed and right-handed versions. Only for neutrinos, only left-handed have been observed. Now what would a right-handed neutrino look like? Well, obviously it would not interact strong or electromagnetic, because after all it's a neutrino. But it also wouldn't interact weak, because it's right-handed. This would explain why it wasn't observed in experiments (because AFAIK Neutrinos are always observed through their weak interaction). On the other hand, it would interact gravitationally, and would therefore make a form of dark matter, without any extension to the standard model, except that one would drop the claim that there are only left-handed neutrinos. Since it seems strange anyway that neutrinos, unlike all other particles, only come in left-handed form, I'd expect that a "sterile" right-handed neutrino would be the natural assumption.
However the fact that particle physicists don't assume that, I guess there are good reasons not to assume it. So what is the problem with this reasoning? And could the sterile neutrino from this story be actually such a right-handed neutrino?
The Tao of math: The numbers you can count are not the real numbers.
Your reasoning looks pretty sound to me; I don't think there is a fundamental reason to assume that right-handed neutrinos don't exist. I think the main reason people make that assumption is that there is no experimental evidence for it. It appears that the weak force only acts on left-handed particles
You're right in that a right-handed neutrino would interact only gravitationally. But if they exist, how did they get created in the first place? That creation process had to involve some combination of the other 3 forces -- gravity doesn't allow for particle creation or decay.
Another thing is that if it were massive (and it would have to be), it would have to have a left and right-handed component, and be invariant under Lorentz transformations. (One way to think about it is this: If it's moving in a certain direction, you could look at it from a reference frame moving even faster in that direction, and it would appear to be going the other way. This would change it from a right-handed to a left-handed particle, which would mean it could interact with the weak force, etc. etc. So it would have to be a mixture of both left- and right-handed components - you can't have a purely right-handed neutrino with a non-zero mass).
It also turns out (mathematically) that you can construct a (sterile) neutrino by using only left-handed fields, and still make it behave as if it had a right-handed component. This is the so-called "Majorana spinor". So you don't really need to invoke right-handed neutrinos, you can get the same result using just the left-handed fields.
Well, it's simple: At big bang, the matter went forward in time into our universe, and the antimatter went backward in time into the anti-universe. :-)
And there we have it. Maxwell's Demon, telling us how it all was done!
May I direct your attention to the three characters at the end of my post? Those letters are:
U+003A COLON
U+002D HYPHEN-MINUS
U+0029 RIGHT PARENTHESIS
You can learn more about the meaning of this character combination at Wikipedia.
Or to make it short:
WHOOSH!
The Tao of math: The numbers you can count are not the real numbers.
Cosmic Gall, by John Updike
NEUTRINOS, they are very small.
They have no charge and have no mass
And do not interact at all.
The earth is just a silly ball
To them, through which they simply pass,
Like dustmaids down a drafty hall
Or photons through a sheet of glass.
They snub the most exquisite gas,
Ignore the most substantial wall,
Cold shoulder steel and sounding brass,
Insult the stallion in his stall,
And scorning barriers of class,
Infiltrate you and me! Like tall
and painless guillotines, they fall
Down through our heads into the grass.
At night, they enter at Nepal
and pierce the lover and his lass
From underneath the bed-you call
It wonderful; I call it crass.
The only physicists I've ever seen in lab coats were in angles and demons.
Angles? Were they so acute they were obtuse?
The mind conceives, the body achieves, the spirit manifests.
So what is the problem with this reasoning? And could the sterile neutrino from this story be actually such a right-handed neutrino?
First: it cannot be dark matter because neutrinos are too light and hence move too fast. The result is that the WMAP cosmic microwave background would be blurred out far more than it is so we know that, whatever the dark matter is, it is slow moving and so not a light neutrino.
Second: MiniBoone has interesting results but have not BY ANY STRETCH of the imagination confirmed the existence of a 4th gen of neutrinos. Their signal is only 0.6% incompatible with background. To claim evidence the standard in the field is 3 std. dev. (or 0.27%) and to claim a discovery it is 5 sigma (0.000057%). Effects like this go away all the time and can easily be caused by errors. This is not a guarantee that theirs will but, to make claims like this you need solid, statistical evidence and they do not yet have that.
Third: we already know that right handed neutrinos exist because the neutrino has a non-zero mass. Any mass term in the Lagrangian mixes left and right helicity states. Effectively what this means is that if you have a left handed neutrino but chase after it faster than it is moving (which you can do because it has a mass) it will be a right handed neutrino to you. So, if there is anything interesting happening here, it is not a "normal" right handed neutrino.
Soo.. 2 wrongs don't make a right, but 3 lefts do?
Isn't Hawking radiation a process where gravitation creates particles?
Not really. It's an electroweak process that actually creates the particle-antiparticle pair.
Maybe a Higgs particle decays into a right-handed neutrino and something else?
No. "Decay" implies a weak interaction. And the weak force only interacts with left-handed particles (or more precisely with the left-handed fields, or components, of a particle).
The Higgs field can couple the left- and right-handed fields of a particle. But when you're talking about "Higgs particle decay", that's a weak interaction, which is only left-handed.
IIUC, if left-handedness depended on the frame of reference, then whether an electron (which very clearly has mass) can interact weakly would also depend on the frame of reference, and that doesn't make sense to me.
That's why you can't have a purely left- or right-handed massive particle. Any massive particle (like an electron) has to have both a left-handed and a right-handed (chiral) component. It also has to be invariant under Lorentz transformations, meaning that as you change reference frames, the particle looks the same. Only massless particles can be purely left-handed or right-handed, and for them chirality and helicity are equal. But not for massive particles.
By the way, the evidence of neutrino oscillations means that the three Standard Model neutrinos must have some non-zero mass, which means they're not purely left-handed. They were once thought to be purely left-handed, but that was when they were thought to be massless. Now we know that they're more like electrons, with a left- and right-handed component.