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Dark Matter, WIMPS, and NASA's Alpha Magnetic Spectrometer Data

samzenpus posted about a year and a half ago | from the not-so-fast dept.

NASA 44

cylonlover writes "Recently the media has been saturated with overly-hyped reports that NASA's Alpha Magnetic Spectrometer may have detected dark matter. These claims may have some justification if the word 'may' is shouted, but they rest on a number of really major assumptions and guesses, some of which are on weak and shifting soil. So just what was seen in the experiment, and what are the possible explanations?"

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The media has not been saturated. (-1)

Anonymous Coward | about a year and a half ago | (#43772885)

Come on. Really? This is the first I've heard about this ... and trust me, I watch TV.

Re:The media has not been saturated. (1)

Anonymous Coward | about a year and a half ago | (#43772931)

No, trust me, the media is saturated. I mean, shit, samzenpus posted an article about it on Slashdot and everything.

Possible explanation? (-1)

Anonymous Coward | about a year and a half ago | (#43772891)

AMS was pointed towards the Slashdot comment sections and noticed just how much of so little substance was being said nowadays.

Never trust... (5, Funny)

Anonymous Coward | about a year and a half ago | (#43772919)

Never trust an Alpha Magnetic Spectrometer with important discoveries. I wouldn't even start considering it useful until it hit Beta.

Re: Never trust... (1)

Redmancometh (2676319) | about a year and a half ago | (#43773153)

That is pretty goddamn funny no lie.

Funny and True (1)

Roger W Moore (538166) | about a year and a half ago | (#43773543)

Never trust an Alpha Magnetic Spectrometer with important discoveries.

What makes this funnier is that it is true! Nobody will really believe that the AMS positron signal is from Dark Matter until we have discovered the Dark Matter itself. It may useful in giving us an idea of where to search. Indeed the earlier discovery by PAMELA of the signal AMS is studying already lead to new models for DM which can explain the lack of anti-protons.

Re:Funny and True (1)

iggymanz (596061) | about a year and a half ago | (#43773635)

your phrase of "until we discover" is funny. most of the dozens of"exotic" subatomic particles we know of are from second, tertiary and high decay products that are more common ordinary things.

by your definition, we've mostly only discovered electrons and protons, even neutrons and neutrinos are detected by reactions that make electrons or protons do something.

Re:Funny and True (1)

Roger W Moore (538166) | about a year and a half ago | (#43779075)

most of the dozens of"exotic" subatomic particles we know of are from second, tertiary and high decay products that are more common ordinary things.

Yes but in these cases we have the 4-momenta measured of most, if not all, the particle in the decay and so can reconstruct the invariant mass of the decaying particle along with other properties like charge and spin. Saying that a massively complex and not fully understood system like the galaxy is producing more positrons than we think it should is a very, very different from saying that we see a mass resonance at a particular value.

For example if instead of showing a mass peak when looking at Higgs to Z boson to muon decays ATLAS has just claimed that there was an 5 sigma excess of high energy muons over what was expected nobody would believe that we had found the Higgs: it might be the Higgs or it might be some background feature that we did not understand. Once you can show that you have 2 muons and 2 anti-muons with one pair give a Z boson mass and the total mass of all 4 producing a peak at 125 GeV/c2 over 5 sigma above the background you then have enough evidence to claim discovery of a new, electrically neutral particle. That is the level of detail which is going to be needed before anyone believes that you have found Dark Matter.

Re:Funny and True (1)

iggymanz (596061) | about a year and a half ago | (#43789375)

it is indeed "most", not all; for example those "little neutral ones" go flying out of the chamber/collision hall undetected at most labs.

you are right that far more evidence is needed, but the cool thing is that the data gathering started in the 1930s with stars in galaxies just not moving the right way. these are exciting times

Re:Funny and True (0)

Anonymous Coward | about a year and a half ago | (#43790979)

There are quite a few decay processes that produce no neutral decay products, and there are also particle detectors that incorporate things for measuring photons produced by the reaction. So while it is "most" in some cases, there are other cases where it is"all," as the GP said.

Re:Funny and True (1)

Roger W Moore (538166) | about a year and a half ago | (#43796637)

go flying out of the chamber/collision hall undetected at most labs.

Yes...and no. They can be indirectly detected by requiring conservation of momentum in a plane transverse to the beam. This is not as good as actually seeing them but we can easily reconstruct W boson decays which involve neutrinos and we can even measure the W boson mass although it is an incredibly complex analysis.

Treasure! (1)

sjbe (173966) | about a year and a half ago | (#43774285)

Nobody will really believe that the AMS positron signal is from Dark Matter until we have discovered the Dark Matter itself.

Maybe the proof is on an island you can only find if you already know where it is. [/piratesofthecarribean]

Blog Spam (1)

MatthiasF (1853064) | about a year and a half ago | (#43772981)

Copy/pasted summary from single source, source has popups harassing for email address and tons of social media buttons, and source adds nothing interesting to the discussion.

Editors/moderators haven't had their coffee today?

Re:Blog Spam (3, Informative)

Black Parrot (19622) | about a year and a half ago | (#43773033)

Usually we don't discuss these things until they appear on the Bad Astronomy blog.

Re:Blog Spam (1)

iris-n (1276146) | about a year and a half ago | (#43773149)

How the source adds nothing to the discussion? I've seen this on slashdot when the story first appeared, and the media coverage was uniformly believing CERN's hype, without a shred of scepticism. This blog has a simple, correct explanation of the physics involved, and its interpretation of the data pretty much agrees with I've been hearing at the University.

This is completely obvious (0)

Anonymous Coward | about a year and a half ago | (#43772999)

If dark matter wasn't so wimpy, why is it hiding in the dark?

Re:This is completely obvious (-1)

Anonymous Coward | about a year and a half ago | (#43773031)

Must be Terr'ists!

Yahoo! to buy Tumblr - $1.1B (-1)

Anonymous Coward | about a year and a half ago | (#43773007)

You need to load up, and load up now. This deal could be a potential gold mine.

Over-saturation is bad! (1)

wonkey_monkey (2592601) | about a year and a half ago | (#43773041)

Recently the media has been saturated with overly-hyped reports that NASA's Alpha Magnetic Spectrometer may have detected dark matter

So here's another story about it. Brilliant.

These claims may have some justification if the word 'may' is shouted

The word is "emphasised." Try it now - read that out loud and shout the word "may."

Re:Over-saturation is bad! (1)

maxwell demon (590494) | about a year and a half ago | (#43775771)

We demand that NASA's Alpha Magnetic Spectrometer may or may not have detected dark matter!

more antimatter near Earth than expected (2)

peter303 (12292) | about a year and a half ago | (#43773123)

The PAMELA probe sees antiprotons in the Van Alen belts. The ISS-AMS sees more positrons than expected. Whatever the ultimate expanation, its interesting to see these surpluses.

The amounts are so small, dozens of protons for PAMELA and hundreds of thousands of positrons for AMS, that they would not be noticeable in human life.

Re:more antimatter near Earth than expected (0, Interesting)

Anonymous Coward | about a year and a half ago | (#43773425)

If someone figures out how to capture and store antimatter on long timescales (even just positronium [wikipedia.org] ), this could be an orbital energy source. It's known that lightning creates antimatter [discovermagazine.com] and ejects it into space [space.com] .

Once a method to capture and store antimatter from lightning has been created, this could be used for a low orbit fuel station. Just because there's a tiny amount detected doesn't mean that a much larger quantity isn't created by thunderstorms and lost to space and/or annihilation events from collisions with matter.

After a design is known to work, a station could be placed in orbit over Jupiter's great red spot for continuous collection.

Re:more antimatter near Earth than expected (0)

Anonymous Coward | about a year and a half ago | (#43774097)

Just because there's a tiny amount detected doesn't mean that a much larger quantity isn't created by thunderstorms and lost to space and/or annihilation events from collisions with matter.

Actually, it does place upper bounds on the quantity that is up there. Even if you ignore that you would need something of significant volume comparable to the Van Allen belt to collect most of the antimatter, and using a generous estimate of what portion of trapped particles are antiprotons, you would get that the entire Van Allen belt contains about 1 picogram of antiprotons (about 100 trillion antiprotons). This corresponds to about 200 kJ of energy, about the same amount of energy in a bite sized Snickers. There is still a significant flux of incoming antiprotons compared to what is trapped, but if you somehow managed to capture all of the incoming antiprotons at the a similar altitude, you're talking about maybe 50-100 kW of power from a structure that would be larger than the Earth and assuming 100% efficiency...

Dark Matter and the Rest of Us (1)

gpronger (1142181) | about a year and a half ago | (#43773255)

I do not believe the issue is it being over-hyped; I would take it as a positive for anything to grab the general public's attention in a positive way for basic science research. Maybe we have a bit of solid marketing here by Michael Turner in coining the term "Dark Matter" for this stuff which grabs the imagination of folk who are outside the small sphere of people who actually understand this (and I would completely acknowledge that I am one).

Is the article a bit "fluffy"? Sure. But if the link was to the IOP, maybe in about 2 weeks, and pulling out my college physics textbooks (oops, they predate this stuff) I might begin to understand the actual theoretical equations behind it. If you churn through the full length of the article it does touch on some meatier topics mentioning WIMPS, supersymmetry, and my favorite the neutralino (just because it sounds cool). Again, yes, lightly, but for the audience targeted doing a pretty decent job of explaining in terms that can be understood and maybe whet the appetite a bit.

And maybe that is the point, sitting here more than a few years past college, I am not likely to go back into to school and study theoretical physics and put together an eloquent equation that pulls all of this together. But, maybe in talking with my kids (in college or college bound) they may pick up the excitement and move the topic forward. Because, in the end it is all marketing. Where are the brightest heading, and what will move forward. If articles like this one sparks some interest, then I'll put up with a bit of fluff (and fully recognize that I would not understand much at all if they broke out the underlying math) if it sways public opinion in favor of basic research, and maybe helps sway a couple of new physicists.

I forsee a book title! "Dark Matter and you: (1)

Gareth Iwan Fairclough (2831535) | about a year and a half ago | (#43773365)

It doesn't matter, not one smegging bit."

Old News With Smaller Error Bars (1)

upmufa (702569) | about a year and a half ago | (#43773617)

The really silly thing about the dust-up with AMS is that the PAMELA experiment (later confirmed by Fermi) made the exact same measurement and is credited with the discovery. AMS just re-did it with smaller error bars. Here's the original PAMELA paper from 2009: http://www.nature.com/nature/journal/v458/n7238/full/nature07942.html [nature.com] (preprint here: http://arxiv.org/abs/0810.4995 [arxiv.org] ) The dark matter interpretation isn't even new. All AMS has brought is smaller error bars.

Fascinating news about the smaller error bars. (0)

Anonymous Coward | about a year and a half ago | (#43773899)

But were the error bars smaller?

Re:Old News With Smaller Error Bars (1)

mbone (558574) | about a year and a half ago | (#43774589)

It also goes to higher energy, and the longer the experiment lasts, the higher the energy range that will be explored (it is count-limited at the highest energies).

Of Particular Significance (2)

mbone (558574) | about a year and a half ago | (#43773809)

People who are interested in these matters should follow Matt Strassler's science blog, Of Particular Significance [profmattstrassler.com] , which covered these same points back at the beginning of April [profmattstrassler.com] , and then again two weeks later [profmattstrassler.com] .

Re:Of Particular Significance (1)

elias2010 (2795201) | about a year and a half ago | (#43779625)

I think there is not dark matter http://t.co/DhiB9Zxp [t.co] [t.co]

why no dark matter black holes? (1)

peter303 (12292) | about a year and a half ago | (#43774233)

If dark matter only reacts to gravity, why doesnt collapse into hgh density clumps over the eons? Ordinary matter is stopped from doing this by the electronmagnetic repulsion of atoms for masses less than a few hundred Jupiters and by hadronic stong force for less than couple Suns.

We would definately notice dark matter signularities, since there is six times more of it than the non-dark kind.

Re:why no dark matter black holes? (0)

Anonymous Coward | about a year and a half ago | (#43774365)

http://www.decodedscience.com/dark-matter-and-black-holes/19885 relevant

Re:why no dark matter black holes? (1)

Anonymous Coward | about a year and a half ago | (#43774457)

It wouldn't collapse into a blackhole if it never gets dense enough. And without electromagnetic interactions, it is much more difficult to form a dense object. If two charged particles collide, the acceleration they experience causes photons to radiate away some of the energy. If you have a pile of charged particles, the interactions will cause radiation of energy, cooling the pile of particles off and causing it to become more dense. Without that interaction, the particles would just all pass through each other, and orbit around the center of mass. You could have a little bit of cooling from evaporative cooling, where particles where occasionally a particle gets flung around enough to get ejected out of the system and carry above average amount of energy with it, but that would be slow, and assumes there is not an equal source of incoming particles too.

Also, if it did form a black hole, for a lot of dark matter candidates, the black hole would be indistinguishable from a black hole made from normal matter. So maybe some portion of black holes we see now is from dark matter. But surveys of the sky have shown there are nowhere near enough black holes to account for the missing matter, so there would still need to be a lot of dark matter in some other form.

Re:why no dark matter black holes? (1)

mbone (558574) | about a year and a half ago | (#43774731)

Gravitational lensing surveys [harvard.edu] have pretty much ruled out [arxiv.org] this Dark Matter explanation for black holes (or any other dark compact objects) with masses > about 10^-7 Solar Masses, and it is very hard to see how smaller black holes could have ever formed.

Re:why no dark matter black holes? (4, Insightful)

habig (12787) | about a year and a half ago | (#43774827)

If dark matter only reacts to gravity, why doesnt collapse into hgh density clumps over the eons? Ordinary matter is stopped from doing this by the electronmagnetic repulsion of atoms for masses less than a few hundred Jupiters and by hadronic stong force for less than couple Suns.

It does, we call those clumps "galaxies".

Note that the virtue of interacting only a little bit with normal stuff (via only the weak and gravitational forces, not gravity alone) actually makes it harder for dark matter to pack in tightly. Why? it's hard for a distribution of dark matter particles to shed kinetic energy and settle down more deeply into the gravitational potential well. Ordinary matter has all sorts of electromagnetic ways to shed energy and cool down.

If this thermal argument is opaque, imagine one WIMP, with some kinetic energy. It falls down towards the center of a galaxy. But, it seldom interacts to lose any energy, so zooms right back out the other side. Sort of a tiny, frictionless pendulum with a galaxy sized amplitude.

Re:why no dark matter black holes? (1)

steelfood (895457) | about a year and a half ago | (#43776697)

This is kinda putting the horse before the cart. The fact that galaxies exist as localized clumping of matter is postulated to be due to this "dark matter" substance that does not interact with anything else, including itself, in any way except by gravity. I.e., dark matter is the proposed explanation for galaxies, not the other way around.

Re:why no dark matter black holes? (1)

VortexCortex (1117377) | about a year and a half ago | (#43778125)

This is kinda putting the horse before the cart. The fact that galaxies exist as localized clumping of matter is postulated to be due to this "dark matter" substance that does not interact with anything else, including itself, in any way except by gravity. I.e., dark matter is the proposed explanation for galaxies, not the other way around.

Speaking of cart drawn horseages...
If gravity warps space time, then we agree space time can be warped. We observe that cosmic background radiation from the big bang isn't perfectly smooth. So, what if the structure of space is just slightly "warped?" Dark matter could just be space time curvature. Instead of the clustering up of galaxies being the result of more matter being present, the matter could just be pooling into places that are already more curved. In other words: You turn on a light, you generate an EM field, You can turn it off and decrease the EM field in the area. You look up at night and see variation in the EM field, not a constant smooth glow... So, when I look up at the night sky and see galaxies, but no dark matter, I simply see variations in the Higgs Field...

Re:why no dark matter black holes? (0)

Anonymous Coward | about a year and a half ago | (#43778395)

There are observations of dark matter that agree with the idea it moves around and behaves like a weakly interacting gas. So it is something that moves around and acts just like matter in the GR equations. If it ends up to be non-interacting and has no detectable particle form, the distinction between whether it is some form of non-interacting matter or just a variation of space that gets dragged around like matter is meaningless.

Also, there is no know connection between the Higgs field and gravity that would result in such variations. Additionally, if the Higgs field behaved differently from place to place like that, it would result in changes to other observations, especially high precision tests of things seen via spectroscopy.

Re:why no dark matter black holes? (1)

elias2010 (2795201) | about a year and a half ago | (#43779369)

I think there is not dark matter http://t.co/DhiB9Zxp [t.co] [t.co]

Improperly worded summary (4, Informative)

AchilleTalon (540925) | about a year and a half ago | (#43775245)

From the summary: "... reports that NASA's Alpha Magnetic Spectrometer ..."

AMS isn't a NASA experiment, it is an international collaboration and NASA is only one among many other collaborators. Source: http://www.ams02.org/partners/participating-institutions/ [ams02.org]

I believe this summary is badly worded letting people think the AMS experiment is even a NASA initiative while it isn't neither. It is a CERN experiment that is taking advantage of the ISS and hence the NASA collaboration. Even other space agencies have contributed in this experiment.

Re:Improperly worded summary (1)

elias2010 (2795201) | about a year and a half ago | (#43779341)

I think there is not dark matter http://t.co/DhiB9Zxp [t.co]

Re:Improperly worded summary (1)

Sockatume (732728) | about a year and a half ago | (#43779707)

NASA didn't even want to launch it, they had to have their arm twisted to schedule an extra Shuttle mission so it wasn't just left on the ground to rot.

dark matter (1)

elias2010 (2795201) | about a year and a half ago | (#43779357)

I think there is not dark matter http://t.co/DhiB9Zxp [t.co] [t.co]

Re:dark matter (0)

Anonymous Coward | about a year and a half ago | (#43782313)

At the end you seem to think Doppler shifting of light is not possible, but it is directly observed in laboratories in many different fields and experiments.
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