Theorists weigh in on where to hunt dark matter

May 22, 2013 by Lori Ann White
Left panel: Air molecules whiz around at a variety of speeds, and some are very fast. When they collide with both heavy and light elements - for example, xenon (purple) and silicon (orange) - these fast moving particles have enough momentum to affect both nuclei. Right panel: Dark matter particles are moving more slowly and are less able to affect the heavy xenon nucleus. As a result, detectors made from lighter materials like silicon may prove to be more effective at picking up signals of dark matter. Credit: Greg Stewart/SLAC National Accelerator Laboratory

(Phys.org) —Now that it looks like the hunt for the Higgs boson is over, particles of dark matter are at the top of the physics "Most Wanted" list. Dozens of experiments have been searching for them, but often come up with contradictory results.

Theorists from the Kavli Institute for and (KIPAC), a joint SLAC-Stanford institute, believe they've come up with an algorithm – a of how the individual particles behave – that could help narrow the search for these elusive particles, which are thought to make up more than 25 percent of the matter and energy in the universe.

It starts with assumptions, said Yao-Yuan Mao, lead author of a paper published in The Astrophysical Journal that outlines their new search tool. Assumptions are a good starting point when you don't know where to look. A popular assumption about is that it's made up of WIMPs, Weakly Interacting . The "M" in WIMP accounts for gravity's ability to herd these particles around; the "P" and "I" hint at why they're so hard to detect otherwise.

Most dark matter detectors are based on the assumption that, every once in a while, a WIMP must smack into the nucleus of an atom of , making the nucleus vibrate and releasing a signal. Such can be detected. But what that disruption looks like and how often it happens depends on yet more assumptions. How heavy is the dark matter particle? How fast is it moving?

Another common assumption that touches on these issues, said Mao, is that collections of WIMPs behave as an ideal gas, a collection of particles that hang out together and occasionally bounce off each other. Sometimes a lucky bounce gives a particle more energy, sending it zooming off at a greater speed. How often particles pick up more energy and more speed depends on how much you turn up the heat or put on the pressure.

But, as far as scientists can tell, turning up the heat and putting on the pressure doesn't affect WIMPs. Only gravity does.

"The Ideal Gas Law doesn't describe a system of particles, like dark matter , that don't seem to transfer energy to each other," said Mao. This incorrect description can distort the carefully built picture upon which a search for WIMPs is based. In particular, it means predictions of their velocities can be off by a significant amount, but velocities affect what a detector will see.

Mao and his colleagues have used simulations to provide new insight into how fast WIMPs are expected to move.

WIMPs that move fast enough to reach escape velocity and leave the dark matter halo that surrounds the Milky Way take themselves completely out of the hunt. That reduction in the number of WIMPs affects how often one hits the nucleus of an atom in a detector. The remaining WIMPs must be moving more slowly than escape velocity, which affects how hard they can hit. If they hit a detector whose atoms are too massive, the WIMPs bounce off without a sign, like pebbles scattering off a boulder. So the trick is to build a detector out of materials that are a good match for the particle's expected mass and speed.

As theorist Louis Strigari, another author on the paper, said, "The heavier the WIMP, the more collisions you can detect." But there's a growing suspicion that WIMPs might be as much as 10 times lighter than previously thought. "If WIMPs do have this low mass," said Strigari, "the model used to describe their behavior would have significant effects on an experiment's result."

In fact, Mao, Strigari and Risa Wechsler, a professor at SLAC and Stanford, are now busy interpreting the results of experiments based on their new description, and they believe it explains some of the conflicting results obtained by such experiments as XENON100 (which uses the fairly heavy element xenon as the material for dark matter to smack into) and the Cryogenic Dark Matter Search II, or CDMS II (which took its readings with detectors made from the much lighter element silicon).

KIPAC member Blas Cabrera is a Stanford physics professor and, as a leader of CDMS II, a dark matter hunter from the experimental side. He said the theorists have made an important contribution. "It really emphasizes that, for light-mass , different types of detectors would have different responses," he said.

"I'm actually hoping we can talk the experimental community into using their model," Cabrera added. "It's important to get everyone to agree to use the same parameters so we're comparing apples to apples instead of apples to oranges."

Explore further: Finding faster-than-light particles by weighing them

More information: iopscience.iop.org/0004-637X/764/1/35/

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vacuum-mechanics
1 / 5 (12) May 22, 2013
Now that it looks like the hunt for the Higgs boson is over, particles of dark matter are at the top of the physics "Most Wanted" list. Dozens of experiments have been searching for them, but often come up with contradictory results.
Theorists from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint SLAC-Stanford institute, believe they've come up with an algorithm – a mathematical description of how the individual particles behave – that could help narrow the search for these elusive particles…

Instead of looking for dark matter from something as particles (such as Higgs boson be), why don't try finding something like Higgs field which was believed to pervade all space of the universe as follow…
http://www.vacuum...14〈=en
SolidRecovery
2.5 / 5 (8) May 22, 2013
Now that it looks like the hunt for the Higgs boson is over, particles of dark matter are at the top of the physics "Most Wanted" list. Dozens of experiments have been searching for them, but often come up with contradictory results.
Theorists from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint SLAC-Stanford institute, believe they've come up with an algorithm – a mathematical description of how the individual particles behave – that could help narrow the search for these elusive particles…

Instead of looking for dark matter from something as particles (such as Higgs boson be), why don't try finding something like Higgs field which was believed to pervade all space of the universe as follow…
http://www.vacuum...14〈=en

You can take science whatever direction. It is not wrong to look into one direction as long as there is supporting evidence.
tadchem
2.2 / 5 (5) May 22, 2013
Is one assumes that dark matter behaves as an Ideal Gas, of a 'molecular' weight no greater than that of a hydrogen atom, the obvious place to 'look' (for a theoretically invisible gas) is interstellar space and the galactic halo. The latter should be detectable by comparing the distribution curves of mass and visible matter as evidenced by photometry and stellar speed measurements.
Thrasymachus
3.7 / 5 (12) May 22, 2013
The latter should be detectable by comparing the distribution curves of mass and visible matter as evidenced by photometry and stellar speed measurements.


"Hmm, our measurements of the speed of stars around galaxies is different from what we'd expect using classical GR. I wonder what could do that?"

"Well, a very hard-to-detect bunch of matter could do it. We could call it Dark Matter, since we don't know much else about it."

"Groovy, now let's see if we can find some evidence that this Dark Matter exists. Where should we look?"

"Well, if Dark Matter were a thing, you'd expect it to change the speeds of stars around galaxies from what classical GR would predict."

"Hey look! The speeds of stars around galaxies is different from what classical GR predicts! Dark Matter confirmed!"

It's a good thing real science doesn't follow the advice of internet commenters.
islatas
4.4 / 5 (10) May 22, 2013
If the physicists would be so obstinate in the research of cold fusion, we would have this technology for seventy years already...


How do you have the energy to post the same thing over and over and over again? It doesn't seem to matter if the article is about energy or how quickly paint dries you bring up cold fusion. Enough. Stop polluting these threads.
SolidRecovery
3.2 / 5 (11) May 22, 2013
If the physicists would be so obstinate in the research of cold fusion, we would have this technology for seventy years already...


How do you have the energy to post the same thing over and over and over again? It doesn't seem to matter if the article is about energy or how quickly paint dries you bring up cold fusion. Enough. Stop polluting these threads.


I have noticed this trend as well. Never adds to the conversation. Same goes for the conservative and liberal debates going on here. All very opinionated and single minded with little to no objective supporting evidence. I ignore those posts, giving them any kind of feed back is counter productive.

I do enjoy the posts that give other points of view for the article without changing the subject. Too bad they are far and few in between.
Noumenon
1.4 / 5 (28) May 22, 2013
"Well, if Dark Matter were a thing, you'd expect it to change the speeds of stars around galaxies from what classical GR would predict."


No, if DM existed observations would match GR predictions.
AntonKole
1.2 / 5 (6) May 22, 2013
One simple experiment in earth orbit, may solve this issue once and for all. In the mean time, we patiently wait .....................
yep
1.5 / 5 (8) May 23, 2013
Dark matter is based on the assumption of an expanding universe. Hubble is given credit for proving this yet, he did not himself believe this was the case as he felt red shift was a luminosity not a distance relationship. Ya'll know what happens when you assume something right?
verkle
2.3 / 5 (9) May 23, 2013
"Hmm, our measurements of the speed of stars around galaxies is different from what we'd expect using classical GR. I wonder what could do that?"

"Well, a very hard-to-detect bunch of matter could do it. We could call it Dark Matter, since we don't know much else about it."

"Groovy, now let's see if we can find some evidence that this Dark Matter exists. Where should we look?"

"Well, if Dark Matter were a thing, you'd expect it to change the speeds of stars around galaxies from what classical GR would predict."

"Hey look! The speeds of stars around galaxies is different from what classical GR predicts! Dark Matter confirmed!"

It's a good thing real science doesn't follow the advice of internet commenters.


Hilarious! But so true. :)

SHREEKANT
1 / 5 (6) May 23, 2013
It is not a dark matter, it is a dark energy. Size of dark matter should not be so small, it size is nearly equal to or greater than the size of atom.

It is true that the team has found the right location of dark energy. only confusion is two atom in same chamber[as shown in diagram? CONGRATS to the 'team'

It will explain gravity, alignment of atoms & molecules at nano-level and many more BASICS...
yep
1 / 5 (6) May 25, 2013
Dark matter dark energy same B.S. Look around our solar system where is it? Around Uranus? What is theory.....Maybe invention?
Fleetfoot
4.3 / 5 (6) May 28, 2013
One simple experiment in earth orbit, may solve this issue once and for all. In the mean time, we patiently wait .....................


Wait no longer, here are the first results:

http://www.ams02....eriment/
Fleetfoot
5 / 5 (5) May 28, 2013
Dark matter is based on the assumption of an expanding universe.


No it isn't, it was first found from the virial theorem applied to galaxy clusters. It also shows up in stellar velocities within galaxies, in the temperature of intra-cluster hydrogen plasma, in the ratios of the products of nucleogenesis, the speed with which galaxies started forming in the early universe and in gravitational lensing, and probably more I've forgotten.

Other than those, it's just a rumour ;-)
AntonKole
1 / 5 (6) May 29, 2013
Wait no longer, here are the first results:

Seen it. Yes, it's definitely great data. And a great collaboration too. Quite impressed. But it hasn't answered the question of 'what' dark matter is. And, it may not ever do so either.

As the old saying goes: 'Why use a sledgehammer to break an egg, when the edge of a pan may do.'
Fleetfoot
5 / 5 (5) May 30, 2013
Wait no longer, here are the first results:

Seen it. Yes, it's definitely great data. And a great collaboration too. Quite impressed. But it hasn't answered the question of 'what' dark matter is. And, it may not ever do so either.


Not yet but if they can increase the detector range to above 1 Tev then they might measure the mass of the particles (or it might be something else entirely). That would let them conduct searches in the LHC etc. and then we could really study them.

As the old saying goes: 'Why use a sledgehammer to break an egg, when the edge of a pan may do.'


All bright ideas for the design of such a pan will be gratefully received, answers on a postcard ....
Shelgeyr
1 / 5 (8) May 30, 2013
Theorists weigh in on where to hunt dark matter


Where? Where? I think their best bet is to hunt right there in Fantasy Land, where they work and where the theory was developed!
AntonKole
1 / 5 (6) May 31, 2013
All bright ideas for the design of such a pan will be gratefully received, answers on a postcard ....

This issue has been discussed here on Phys.org in detail before. To answer your request, I've supplied a link for you. To avoid a repeat of the past lengthy discussion, please refer any future queries on the link supplied. Thanks.
( https://www.faceb...59787252 )
Fleetfoot
5 / 5 (2) Jun 01, 2013
All bright ideas for the design of such a pan will be gratefully received, answers on a postcard ....

This issue has been discussed here on Phys.org in detail before. To answer your request, I've supplied a link for you. To avoid a repeat of the past lengthy discussion, please refer any future queries on the link supplied. Thanks.
( https://www.faceb...59787252 )


From the front page:

F = G (m_1 * m_2) / d^2

Since that is wrong, I'll not bother about how you derive it. If you want to try again, this is what you need to derive:

https://en.wikipe...cal_form

or you could try for one of the pseudo-Newtonian forms but these are thought to be marginally in some recent tests while GR is accurate:

http://en.wikiped..._gravity

http://en.wikiped..._gravity

http://en.wikiped...iki/STVG
ValeriaT
1 / 5 (6) Jun 01, 2013
Now that it looks like the hunt for the Higgs boson is over, particles of dark matter are at the top of the physics
IMO the dark matter particles are formed with neutrinos and they do exist in many species in the same way, like the Higgs particle itself (chameleon particle). This similarity isn't accidental, because the Higgs particle represents the dark matter particle at the quantum scale. IMO the Higgs observed is actually just a first member from line of another four bosons, which would exhibit charge and which are manifestation of AdS/CFT correspondence to dark matter. Illustratively speaking the geometry of energy scattering at the large scales is geometrically similar to scattering at short scales. It means that the Higgs boson is manifestation of nodes of quantum foam of dodecahedral geometry, which is quite similar to dark matter foam observable in CMBR power spectrum.
ValeriaT
1 / 5 (6) Jun 01, 2013
Anyway, the dark matter is bonanza for theorists. During time the physicists proposed dozens of theoretical models, which could be ordered by the rest mass of particle considered into line

...scalar field, quintessence, mirror matter, axions, dilatons, inflatons, heavy photons, fat strings, sterile neutrinos, chameleon particles, dark fluid and dark baryons, fotinos, gravitinos and WIMPs, SIMPs, MACHOs, RAMBOs, DAEMONs and micro-black holes...

..and I probably missed many others. CDMS suggests a WIMP mass of 8.6GeV; AMS-02 indicates 300GeV or more; and we also have the Weniger line at Fermi which would imply a WIMP mass around 130−150GeV. These numbers are apparently inconsistent with each other and probably all artifacts, which have nothing to do with WIMPS.

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