Polar Detector Spots Neutrinos

C. Mattix writes "It looks as though they finally got some - MSNBC has a story on the polar station that detected neutrinos. " It's got a good explanation of the AMANDA station and what they're doing - not the heaviest scientific article, but good to read.

Comments

Woohoo!!

[HerrGlock]

So that means that they have discovered something that does nothing? Invisible, has no mass and travel at fantastic speeds?

You mean they have finally discovered ill-suited laws that Congress tries to pass? Wow.

Maybe they should have set up camp in Washington DC.

DanH
Cav Pilot's Reference Page

Re:Woohoo!!

[Jace of Fuse!]

So that means that they have discovered something that does nothing? Invisible, has no mass and travel at fantastic speeds?

And they went one mile below the surface of the south pole just to find it.

Maybe they should have set up camp in Washington DC.

No, the device is sensitive to Muons, not Morons.

"Everything you know is wrong. (And stupid.)"

six for six

[diagnosis]

So the neutrino was the last of the leptons and quarks for which there was not experimental evidence. Now what?

Good history (although the translation from French is kind of amusing) here

and this background info is a little better (also, there is more yellow on the page :)
http://www.ps.uci.edu/~superk/neutrino.html

Re:six for six

[Anonymous Coward]

There has been "experimental evidence" for neutrinos for years. Other experiments have been detecting them. The problem has been the eficiency of the detectors. Since neutrinos don't interact readily with matter you need a heck of a lot of matter (ie the earth and some thick ice) to get a reasonable number of interactions to produce photons that you can detect. Other experiments use huge tanks of heavy water surrounded by photomultiplier tubes deep underground or tanks of 1,1,1-tricholoroethane (dry-cleaning fluid). One of the great mysteries is the observed neutrino flux from the sun. Current astrophysical models predict between 1.5 and 2 times the number of neutrinos from the sun than we observe (IIRC). Part of this may be due to inefficiency in our detectors, errors in our theories of stellar behaviour or errors in our theories of fundamental particles.

Re:six for six

[Basalisk]

Just for those that don't understand what leptons and quarks are, here's particle physics 101:

Leptons are the 'light particles'. they have less mass than most other commonly seen particles. There are six types. The electron, the muon, the tauon, and the neutrino. Now that looks like only four because their are three types of neutrino, the elctron neutrino, the muon neutrino and the tauon neutrino.There are three types so that the 'families' are preserved.

Now the nuetrino was introduced in order to preserve a quantity known as spin. All the leptons have spin 1/2, and are fermions. Fermions are particles that follow the Pauli exclusion principle, so no two fermions are in the same quantum state. Now when a neutron decays into a proton and an electron, charge is preserved, whoever spin isn't, because the neutron has spin +-1/2, the proton has spin +-1/2, and so does the electron. In order to get the spins balancing, you need a neutral extra spin 1/2 particle.

Now about those 'familys' I mentioned earlier? Well, only the electron is stable among the non-neutrino leptons. The others decay into an electron and a bunch of neutrinos. However the number of particles in each family remains constant. So when a muon decays (1 muon), it decays into an electron (1 electron), a muon netrino (1 muon) and an electron _anti_neutrino (-1 electron)

So there are six leptons, tauons and muons decay into electrons, but leave behind neutrinos of the same family.However, the universe would not be at all interesting with only leptons. There are quarks as well.

There are also six flavours of quarks. This may or may not be coincidence. Last I checked physicists were unsure if there was a link between quarks and leptons. The six quarks are Up and Down, which form protons, and other stuff that decays into protons (and various leptons). There is strange and charmed, and top and bottom, which make up weird particles that tend to be heavier.

Quarks are never seen alone. They bind together in groups of three or two, and have a charge of +2/3 or -1/3. Now a group of three quarks (called a baryon or heavy particle), such as a proton would have two quarks with a charge of +2/3 and one with a charge of -1/3. I think a proton is uud. Now a neutron(ddu) turns into a proton when one of it's down quarks turns into an up quark, an electron, and two neutrinos. It does this using the weak force, which I'll get to later. Quarks also come in groups of two, which are a quark and an antiquark. These are mesons. They tend to be things like !ud or !du.

So you now have leptons, that help balance things and quarks, that stick together. But what forces act on them? Four. Gravity, Electromagnetism, Weak and Strong nuclear forces.

The strong force is what groups quarks together. All quarks have a color, red, green, or blue. Now in a baryon or meson, the overall color must be white. So a baryon is made up of a red quark, a green quark, and a blue quark. A meson usually has a blue colored quark and an antiblue colored antiquark. Or red/antired, or green/antigreen. As long as no red green or blue shows, the universe is happy. All this is kept in check by the strong force and it's messenger particle, the gluon. Gluons carry color between quarks. If a red quark changes to a green quark, a red/antigreen gluon is emmited, and when it hits a green quark, the antigreen and green colors cancel, and the previously green quark becomes red.

Then there is the weak force. The weak force changes things. It is responsible for the changes in a neutron that cause it to decay. There are three carrier particles for the weak force W+,W- and Z. they carry electrical charges of +1,-1, and 0 respectivly. Now when the d quark in a neutron decays, it emits a W-. the charge is conserved by the W- taking away -1 from the -1/3 to give a +2/3 charge. Now we have a u quark and a W-. the W- then decays into an electron and an electron antineutrino.

Then there is the electromagnetic force, which has as its messenger the photon. Now when two electrons pass by each other and deflect, a pair of photons is exchanged. These photons, like all the other messenger particles are virtual. They only exist for a fleeting second, and don't do much apart from tell the particles what to do. Electromagnetism only talks with particles with electric charge.

Finally there's gravity. Physicists havent yet got Quantum gravity, so they don't yet know how to fit it in with everything else. It's carrier is called the graviton, but nobody has yet caught a live one. Mostly because the energy needed to turn a virtual graviton into a real one is huge.

One last thing. The messenger particles are all bosons, so the can be acting cohesivly in a group. This gives things like lasers their intensity. Fermions can't do this, so you'll never see a easer.

The reason neutrinos are so hard to spot is because the have no mass, they don't interact gravitationally, they are electrically neutral, so they don't talk electromagnetism, and they aren't a quark, so they don't talk colors with the strong force. They can only be detected by their interaction with other particles through the weak force. This is what makes spotting them big physics.

BTW, remember that I may be wrong. IANAPhysicist.

Re:six for six

[volsung]

You don't teach this stuff at the high school level. You have to first try and get across ideas like force, energy, work, power, acceleration, etc. often without the benefit of calculus. (Your school may vary.)

Re:six for six

[krlynch]

Bravo! Most of my particle physics colleagues couldn't give a better brief explanation. In less than a page, you've succeeded in summarizing the last fifty years or so of high energy physics brilliantly!

I did want to mention one thing. You said:Last I checked physicists were unsure if there was a link between quarks and leptons.

In fact, we are pretty darn sure that there IS a link. We don't know exactly why there are three families (or generations) of fermions (although there are many ideas out there), but we DO have a good understanding of why there are as many leptons as there are quarks. In fact, the reason we believed for many years that there was a top quark and a tau neutrino is that they HAD to be there.

The reason is a tad technical, and has to do with something called gauge anomaly cancellation. If the number of leptons and quarks was NOT the same, then some of the symmetries of the theory that we actually see in nature would be destroyed by certain "one loop Feynman graphs" that connect three gauge bosons (the triangle graphs). But, with the same number of quarks and leptons, the gauge anomalies of the standard model cancel, and all is right with the current theory of the universe. In fact, gauge anomaly cancellation is nearly a requirement for any model to be taken seriously, and is one of the first things people ask about when someone presents a new model.

Re:six for six

[krlynch]

Part of this may be due to inefficiency in our detectors, errors in our theories of stellar behaviour or errors in our theories of fundamental particles.

The problem is almost certainly (i.e. hundreds of physicists have bet their careers on it) in our theory of fundamental particles. The discrepancy is absolutely not due to detector inefficiency (the same types of experiments obtain the expected neutrino flux from nearby experiments); the detection efficiency for neutrinos is very low, but if you build a big enough detector, it doesn't kill you. Furthermore, many different experiments using very different techniques obtain results that (roughly) agree on the disagreement. And while there are problems with the stellar models, the same calculation that tells you how many neutrinos come out also tell you how many photons come out and what the surface temperature of the sun should be, and the photon flux and temperature measurements are dead on. Further, the stellar models make predictions about things like "sun-quakes" (the spectrum of solar acoustic surface waves) that are, I believe, also dead on. So, while there is room for improvement in both the experiments and the stellar models, they are not reallly suspect in the solar neutrino problem.

Further evidence that it is the fundamental particle physics that is wrong is that there is a measurable azimuthally dependent flux (angle above versus below the horizon) of atmospherically produced muon neutrinos; the Standard Model predicts no such behavior.

In fact, the best (educated) guess at this point is that neutrinos are able to "oscillate" between the different types, and that the neutrinos from the sun change from electron type to some other type during the time it takes to get from the sun to the earth. Thus, when they get here, some of them are no longer in a form that can be detected by the experiments to date.

Now, I don't think that AMANDA can tell us anything about the solar neutrinos (it looks at very high energy muon type neutrinos, not the low energy electron type), but there are experiments such as SNO in Canada that should be able to access the low energy neutrinos and give us some more information about the solar neutrino problem.

Why neutrino telescopes matter

[sita]

Neutrinos do of course interact with matter but just through the weak interaction. The weak interaction is just that, weak. That means the probability that a neutrino will interact is low, and that you need a lot of them and cover a lot of volume to see anything. That's why Amanda (and Antares and other neutrino experiments) have to be huge.

Now, this low interaction probability is also good. Ordinary telescopes detect electromagnetic radiation (light, radio waves etc), however photons do scatter of the interstellar medium and even off the background radiation (for high enough energies of the radiation). This means that for long distances the vision of such telescopes is blurred. Neutrinos on the other hand don't scatter (with any significant probability) on the interstellar medium etc so it makes for "sharper images" of the universe if you can build a telescope that can see neutrinos.

What you can study is sources that emit neutrinos (of course). Points of interest could be e.g. active galactic nuclei. Also, it has been hypothethized that supersymmetric particles could account for a significant portion of dark matter. The lightest susy particle (the neutralino) has to be stable and would accumulate in the center of heavy objects (such as the Earth or the Sun) because of gravity. There the concentration would be high enough that they could annihilate with their antiparticles, and produce neutrinos.

This entirely off the top of my head. I used to share office with Amanda people a couple of years back.

Hats off for Amanda. It's just a lovely piece of engineering (and interesting science)!

AMANDA Home Page

[martyb]

For those who may be interested in some additional technical details, please check out the AMANDA home page at: http://amanda.berkeley.edu/amanda/amanda.html.

It provides info on the history of the project (AMANDA-A, -B, and -II) as well as lots of links to many other resources and references.

Re:Detectors

[Anonymous Coward]

No, Winconsin's PSL had nothing to do with these detectors. In fact, unlike the horribly complicated huge machinery used in 'high-energy particle physics' labs (aka Fermilab, SLAC, CERN, DESY, ...) detecting neutrinos doesn't require complicated machinery.

Just have a look at this image from the construction of the Superkamiokande Neutrino Detector. The photomultiplier tubes ("mushrooms") used there are very much similar to those used for the AMANDA detector. You can see two of the AMANDA sensors here, together with the glass pressure globes they're put in before deployment.

I know this - have been working for the AMANDA group once, when we were calibrating the first PMT's for AMANDA back in 1995. It's done at Desy Zeuthen near Berlin. And we were using Linux boxes in the lab for data aquisition purposes ;-)

The nifty thing about AMANDA aren't the PMT tubes but the pressure globes they are put in (1500m of solid ice do exert some force ...). I've got one of the predecessors (used for the BAIKAL experiment) at home, it's cool telling people at a party that the salad bowl has once been at 1500m depth in Lake Baikal.

By the way, did someone notice that the AMANDA logo is a Penguin ?

I wonder how well the reporter understood this?

[meckardt]

Pretty good article, but I got the impression that the person writing it didn't quite understand what was going on. He said this was the first time that neutrinos were detected, and then immediately quoted one of the AMANDA researchers as saying it was the first time a new, higher energy neutrino had been detected.

Interesting to here that they plan to construct a larger particle detector.

Re:Neutrinos?!

[Hater's Leaving, The]

You reply is too harsh. Indeed, he seems to be gibbering, but that's because he's read pseudo-scientific or non-scientific material which has turned things into black and white.

Neutrinos rarely interact with normal matter, and that makes them very hard to detect. However, if you're prepared to throw a whole array of sensors around a huge vat of water (not just water) in a location where _other_ nuclear interactions are minimal (e.g. away from the surface of the earth), and you're prepared to wait for enough time, you will occasionally see what are predicted to be the results of neutrino interactions. You don't actually detect the neutrinos, but they have a 'fingerprint' that is easy to recognise, and no other interaction causes that fingerprint.

Don't flame - inform instead.

THL
--

Re:Neutrinos - AMANDA is more than "detection"

[Monopolist]

This isn't completely true. Earlier radio-chemical experiments like Homestake and SAGE were of the "Oops, there one was" variety. More modern detectors, like SuperK do detect the neutrino direction by detecting the charged particle (like an electron or muon) following a neutrino interaction in the detector -- the higher the neutrino energy the better the pointing. SuperK relied on their ability to track neutrinos when they published their results in support of neutrinos having mass a couple years ago. IMHO, one of the really cool things about AMANDA is that they are deep in ice and not a big tank of water. It was "built" by dropping long strings of detectors into melted columns in the ice. With neutrino detectors bigger is better; a detector like AMANDA could be improved by dropping more detectors into the ice. To improve on a detector like SuperK you need to dig a bigger hole underground and make a bigger tank of water -- something which may be a more difficult engineering problem.

Article seems more precise than our criticism

[IanWestray]

C'mon, popular science reporting is frightening, but are we so scared we can't read the thing carefully before we bash it?

This article clearly states these were the first neutrinos seen by AMANDA:

THE FIRST SIGHTING of the high-energy particles called neutrinos with the AMANDA Telescope...

In the next paragraph it correctly characterizes the novelty as having to do with the level of energy in the neutrinos observed:

"We have a unique probe with a sensitivity well beyond other experiments, and the neutrinos we've seen are of a higher energy than has been seen before," Francis Halzen, a physicist at the University of Wisconsin, said in a statement.

It skimmed the surface, granted, but the article doesn't make the errors we're accusing it of. What gives?

You can't expect much better of MSNBC; after all, they have all the science headlines under "Technology," their industry-conquering "boy we sure are innovative" section.

Crap

[Hard_Code]

Well that's it, party's over. No more constructing secret underground bunkers of round-the-clock keg parties with swimsuit models, all under the guise of "government research". Thanks *alot* guys.

Re:More practical stuff

[lowder]

They don't dig out the entire volume; the photodetectors are placed on cables and lowered into narrow holes about 60 cm wide and 2 km deep. The holes are melted using high pressure hot water. After the photodetectors are lowered in, the water freezes back into ice. So most of the detector volume is actually pristine ice. At the large depths where photodetectors are deployed, the pressure "squeezes out" bubbles and cavities, and the ice is very pure, so light can travel long distances and few photodetectors are required to cover a large volume...

(I am a former member of the AMANDA collaboration, BTW...)

Re:What the heck do they do?!

[Explo]

Why would detecting nutrinos matter at all? The article said something about knowing the path that the nutrino came from...uhm so what? It is most likely so far out in space we have no idea where it originated. And knowing where it came from matters how? Didn't they say things like stars give them off? Pick a star, there you go, theres an origin for nutrinos. Can we detect how old they are, if they contain life or anything like that, from what I understand - no. Then why are we spending all this money to look at things that ar invisible (and yet that makes sense) instead of putting it in something worthwhile?

Oh well. If something does not have immediately apparent practical use, it's not worth anything to study? I guess we'd still be in the middle of dark ages if this guideline would have been strictly adhered to. Everything does NOT have immediately apparent practical applications.