World's most sensitive dark matter detector completes search

July 21, 2016, Brown University
The LUX Dark Matter Experiment operates a mile underground at the Sanford Underground Research Facility. It's location helps shield the detector from background radiation that could confound a dark matter signal. Credit: C. H. Faham

The Large Underground Xenon (LUX) dark matter experiment, which operates beneath a mile of rock at the Sanford Underground Research Facility in the Black Hills of South Dakota, has completed its silent search for the missing matter of the universe.

Today at an international dark matter conference (IDM 2016) in Sheffield, U.K., LUX scientific collaborators presented the results from the detector's final 20-month run from October 2014 to May 2016. The new research result is also described with further details on the LUX Collaboration's website.

LUX's sensitivity far exceeded the goals for the project, collaboration scientists said, but yielded no trace of a dark matter particle. LUX's extreme sensitivity makes the team confident that if dark matter particles had interacted with the LUX's xenon target, the detector would almost certainly have seen it. That enables scientists to confidently eliminate many potential models for dark matter particles, offering critical guidance for the next generation of dark matter experiments.

"LUX has delivered the world's best search sensitivity since its first run in 2013," said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for the LUX experiment. "With this final result from the 2014 to 2016 search, the scientists of the LUX Collaboration have pushed the sensitivity of the instrument to a final performance level that is four times better than the original project goals. It would have been marvelous if the improved sensitivity had also delivered a clear dark matter signal. However, what we have observed is consistent with background alone."

Dark matter is thought to account for more than four-fifths of the mass in the universe. Scientists are confident of its existence because the effects of its gravity can be seen in the rotation of galaxies and in the way light bends as it travels through the universe, but experiments have yet to make direct contact with a dark matter particle. The LUX experiment was designed to look for weakly interacting massive particles, or WIMPs, the leading theoretical candidate for a dark matter particle. If the WIMP idea is correct, billions of these particles pass through your hand every second, and also through the Earth and everything on it. But because WIMPs interact so weakly with ordinary matter, this ghostly traverse goes entirely unnoticed.

The LUX detector consists of a third-of-a-ton of cooled liquid xenon surrounded by powerful sensors designed to detect the tiny flash of light and electrical charge emitted if a WIMP collides with a xenon atom within the tank. The detector's location at Sanford Lab beneath a mile of rock, and inside a 72,000-gallon, high-purity water tank, helps shield it from cosmic rays and other radiation that would interfere with a dark matter signal.

The 20-month run of LUX represents one of the largest exposures ever collected by a dark matter experiment, the researchers said. The rapid analysis of nearly a half-million gigabytes of data produced over 20 months was made possible by the use of more than 1,000 computer nodes at Brown University's Center for Computation and Visualization and the advanced computer simulations at Lawrence Berkeley National Laboratory's National Energy Research Scientific Computing Center.

Careful calibration

The exquisite sensitivity achieved by the LUX experiment came thanks to a series of pioneering calibration measures aimed at helping scientists tell the difference between a dark matter signal and events created by residual background radiation that even the elaborate construction of the experiment cannot completely block out.

"As the charge and light signal response of the LUX experiment varied slightly over the dark matter search period, our calibrations allowed us to consistently reject radioactive backgrounds, maintain a well-defined dark matter signature for which to search and compensate for a small static charge buildup on the Teflon inner detector walls," said Dan McKinsey, professor of physics at the University of California, Berkeley, senior faculty scientist at Lawrence Berkeley National Laboratory, and co-spokesperson for the LUX experiment.

One calibration technique used neutrons as stand-ins for WIMPs. By firing a beam of neutrons into the detector, scientists were able to carefully quantify how the LUX detector responds to the signal expected to be produced from a WIMP collision. Other calibration techniques involved injecting radioactive gases into the detector to help distinguish between signals produced by ambient radioactivity and a potential dark matter signal.

These calibration measures, used for the first time with LUX, helped scientists meticulously search through a wide swath of potential parameter space for dark matter particles.

The LUX dark matter detector is surrounded by light sensors that can detect the emission of just a single photon. Those sensors are designed to capture the tiny flash of light emitted if a dark matter particle were to interact with the detector's xenon target material. Credit: Matt Kapust/ Sanford Underground Research Facility

"These careful background-reduction techniques and precision calibrations and modeling have enabled us to probe dark matter candidates that would produce signals of only a few events per century in a kilogram of xenon," said Aaron Manalaysay, the analysis working group coordinator of the LUX experiment and a research scientist from the University of California, Davis, who presented the new results in Sheffield.

"We worked hard and stayed diligent over more than a year and a half to keep the detector running in optimal conditions and maximize useful data time," said Simon Fiorucci, physicist at Lawrence Berkeley National Laboratory and science coordination manager for the experiment. "The result is unambiguous data we can be proud of and a timely result in this very competitive field—even if it is not the positive detection we were all hoping for."

The quest continues

While the LUX experiment successfully eliminated a large swath of mass ranges and interaction-coupling strengths where WIMPs might exist, the WIMP model itself, "remains alive and viable," said Gaitskell, the Brown University physicist. And the meticulous work of LUX scientists will aid future direct detection experiments.

"We viewed this as a David and Goliath race between ourselves and the much larger Large Hadron Collider (LHC) at CERN in Geneva," Gaitskell said. "LUX was racing over the last three years to get first evidence for a dark matter signal. We will now have to wait and see if the new run this year at the LHC will show evidence of dark matter particles, or if the discovery occurs in the next generation of larger direct detectors."

Among those next generation experiments will be the LUX-ZEPLIN (LZ) experiment, which will replace LUX at the Sanford Underground Research Facility.

Compared to LUX's one-third-ton of liquid xenon, LZ will have a 10-ton liquid xenon target, which will fit inside the same 72,000-gallon tank of pure water used by LUX to help fend off external radiation.

"The innovations of the LUX experiment form the foundation for the LZ experiment," said Harry Nelson, University of California, Santa Barbara, and spokesperson for LZ. "We expect LZ to achieve 70 times the sensitivity of LUX. The LZ program continues to pass its milestones, aided by the terrific support of the Sanford Lab, the Department of Energy and its many collaborating institutions and scientists. LZ should be online in 2020."

LUX, the first major astrophysics experiment in the Davis Campus of the Sanford Underground Research Facility (Sanford Lab), was installed in 2012. Sanford Lab is located in the former Homestake Gold Mine in Lead, S.D. A South Dakota-owned facility, it is managed by the South Dakota Science and Technology Authority (SDSTA), which reopened the mine in 2007 with $40 million in funding from the South Dakota State Legislature and a $70 million donation from philanthropist T. Denny Sanford. The U.S. Department of Energy (DOE) supports Sanford Lab's operations.

"The global search for dark matter aims to answer fundamental questions about the makeup of our universe. We're proud to support the LUX collaboration and congratulate them on reaching this higher level of sensitivity," said Mike Headley, executive director of the SDSTA. "We're looking forward to hosting the LUX-ZEPLIN (LZ) experiment, which will provide another major step forward in sensitivity."

The LUX scientific collaboration, which is supported by the DOE and National Science Foundation, includes 20 research universities and national laboratories in the United States, the United Kingdom and Portugal.

Over the next few months, LUX scientists will continue to analyze the crucial data that LUX was able to provide, in hopes of helping future experiments finally pin down a .

"LUX has done much more in terms of its sensitivity and reliability than we ever expected it to do," Gaitskell said. "We always want more time with our detectors, but it's time to take the lessons learned from LUX and apply them to the future search for ."

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35 comments

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BartV
2.4 / 5 (14) Jul 21, 2016
...has completed its silent search for the missing matter of the universe.


Is this a purposeful play on words? The silent search is still silent even after 1.5 years. Hard for the DM advocates to swallow. Time to move on to some other theory.

antialias_physorg
4 / 5 (16) Jul 21, 2016
Is this a purposeful play on words? The silent search is still silent even after 1.5 years. Hard for the DM advocates to swallow.

OK, time to teach you how to read (yet again *sigh*). You didn't even get to the third paragraph before making another one of your ultra-stupid posts.

Did you notice this sentence in the article?
That enables scientists to confidently eliminate many potential models for dark matter particles

or this
theoretical CANDIDATE
(emphasis mine)
or this
While the LUX experiment successfully eliminated a large swath of mass ranges and interaction-coupling strengths where WIMPs might exist


DM isn't one theory. It is a category for a whole host of theories. The label DM just descibes "that effect which we observe but cannot yet explain" (it doesn't even say the effect is necessarily cause by matter).

So unless you disagree with actual observation of the nigh sky you, too, are "DM advocate"
SCVGoodToGo
4.3 / 5 (12) Jul 21, 2016
@BartV

A null result is still a result; but I wouldn't expect you to understand.
Phys1
3.9 / 5 (7) Jul 21, 2016
SOT certainly is an interesting proposal.
This can be tested with SOE (Some Other Experiment).
Ever considered a career in cosmology ?
Da Schneib
3.9 / 5 (7) Jul 21, 2016
So what has been eliminated? And more important, what remains?
antialias_physorg
4.1 / 5 (9) Jul 21, 2016
So what has been eliminated? And more important, what remains?

From the abstract of this
https://arxiv.org...211.3788
The goal of the LUX detector is to clearly detect (or exclude) WIMPS with a spin independent cross section per nucleon of 2×10^−46 cm2


I.e. for WIMP theories stuff with a lower cross section remains.
Jim4321
5 / 5 (5) Jul 21, 2016
Does anyone know if this is significantly below the neutrino/nucleon cross-section?
Protoplasmix
4.2 / 5 (5) Jul 21, 2016
Does anyone know if this is significantly below the neutrino/nucleon cross-section?
Looks to be comparable but don't quote me – the Ultimate Neutrino Page has for the neutrino-nucleon elastic c.s.:
σ_νn→νn(E) ≈ 9.3E-48 m² (E_ν / 1 MeV)² = 9.3E-44 cm² (E_ν / 1 MeV)², and
σ_νρ→νρ(E) ≈ 6.0E-50 m² (E_ν / 1 MeV)² = 6.0E-46 cm² (E_ν / 1 MeV)².
bschott
2.6 / 5 (10) Jul 21, 2016
@BartV

A null result is still a result; but I wouldn't expect you to understand.

He understands completely.
Time to move on to some other theory.

But he wouldn't expect you to understand that he understands.
Phys1
3.8 / 5 (10) Jul 21, 2016
@BartV

A null result is still a result; but I wouldn't expect you to understand.

He understands completely.
Time to move on to some other theory.

But he wouldn't expect you to understand that he understands.

Are you two room mates ?
mungoooo
3.4 / 5 (7) Jul 21, 2016
". LUX's extreme sensitivity makes the team confident that if dark matter particles had interacted with the LUX's xenon target, the detector would almost certainly have seen it. That enables scientists to confidently eliminate many potential models for dark matter particles, offering critical guidance for the next generation of dark matter experiments."

How would one calibrate such a machine sans a priori knowledge of the signal that they were looking for? It seems to defy even the most basic of rigors. ", maintain a well-defined dark matter signature " ...", scientists were able to carefully quantify how the LUX detector responds to the signal expected to be produced from a WIMP collision.

What led them to expect that? Where did they get the idea that that's what this so called dark matter is?

mungoooo
2.8 / 5 (9) Jul 21, 2016
"It would have been marvelous if the improved sensitivity had also delivered a clear dark matter signal. However, what we have observed is consistent with background alone.""

Well, it's really cool that they didn't just make stuff up, like the LIGO people did, but what would be a 'clear dark matter signal'? What would be this gravity producing...nothing?
mungoooo
3.5 / 5 (8) Jul 21, 2016


""These careful background-reduction techniques and precision calibrations and modeling have enabled us to probe dark matter candidates that would produce signals of only a few events per century in a kilogram of xenon,"

And yet would have enough mass to warp the space time required to hold together a galaxy?

""We expect LZ to achieve 70 times the sensitivity of LUX. "
and if it reveals again nothing...then will you stop insisting that a question mark really is the answer to its own question?
bschott
2.8 / 5 (9) Jul 21, 2016
@BartV

A null result is still a result; but I wouldn't expect you to understand.

He understands completely.
Time to move on to some other theory.

But he wouldn't expect you to understand that he understands.

Are you two room mates ?

Why, did your mom kick you out and you are looking for a place to stay?
shavera
4.1 / 5 (14) Jul 21, 2016
mungoooo: you maybe don't understand how dark matter detection works. They're not looking for the gravitational interaction of these particles, that'd be impossible with our current technology. They're looking for one of these particles to 'bump into' an atom in the detector and in so doing cause something interesting to happen that produces light. For a wide variety of reasons, we don't expect that these particles 'bump into' normal matter very often, if at all. They pass through it like neutrinos do, but with even fewer reactions than neutrinos (they may, in fact, be some variety of neutrino as yet undiscovered).

But how often they bump into normal matter has no bearing whatsoever on their ability to attract gravitationally, so the point you raise in the second comment is meaningless. Interaction cross-section isn't necessarily related to the underlying mass of the particle.
RealityCheck
3 / 5 (7) Jul 21, 2016
Hi all. :)

I'd like to congratulate/thank the LUX team for their honest scientific efforts. Their Report of Null Results for their years long DM search experiment run is commendable both for its scrupulously objective efforts and its honest report of Null results. Refreshing after Bicep2 and LHC 'claims' to date

Alas, these results are not good news for DM enthusiasts. Many OTHER possible "candidates" have already been discounted in other efforts; leaving very little, if any at all, 'wiggle room' for DM 'optimists'.

Re the "interactivity' of whatever DM "candidate(s) are presumed to have with the matter:

If DM can interact with matter (even at low expected rate as per LUX scenario), then our night sky across cosmological distances should be swamped with radiation from such interactions because of the HUMONGOUS QUANTITY of ORDINARY MATTER recently increasingly being discovered distributed across billions of light years of (previously assumed) 'empty' space!

Cheers. :)
swordsman
2.7 / 5 (7) Jul 21, 2016
They successfully discovered nothing! I can easily do that at a much lower cost.

Just another example of the lack of understanding dark matter. The measurements were made almost a century ago.
Urgelt
3.9 / 5 (11) Jul 21, 2016
swordsman wrote, "They successfully discovered nothing! I can easily do that at a much lower cost."

I really don't understand why so many science deniers bother to visit this site. They are unable to grasp even the most elementary principles of scientific investigation.

A null dark matter detection from a carefully-designed experiment is not equivalent to a null dark matter detection from pooping in your hands. The first helps to rule out some, not all, candidate explanations for dark matter effects seen in cosmological observations. The second just gets your hands dirty, though it is undeniably cheaper.

Benni
2.5 / 5 (8) Jul 21, 2016
The new headline should read:

IT HAS BEEN DISCOVERED THAT MOST OF THE UNIVERSE IS NOT MISSING
Da Schneib
2.3 / 5 (3) Jul 21, 2016
2×10^−46 cm2
Wow, that's like 8 orders of magnitude smaller than a neutrino.

On edit But then I saw:

Looks to be comparable but don't quote me – the Ultimate Neutrino Page has for the neutrino-nucleon elastic c.s.:
σ_νn→νn(E) ≈ 9.3E-48 m² (E_ν / 1 MeV)² = 9.3E-44 cm² (E_ν / 1 MeV)², and
σ_νρ→νρ(E) ≈ 6.0E-50 m² (E_ν / 1 MeV)² = 6.0E-46 cm² (E_ν / 1 MeV)².
Hmmmm. OK. Maybe not so much smaller.
wkingmilw
3 / 5 (2) Jul 22, 2016
No discussion of the recent hypothesis that dark matter consists of middle weight black holes surrounding galaxies. Oh well.
epoxy
Jul 22, 2016
This comment has been removed by a moderator.
antialias_physorg
3.5 / 5 (8) Jul 22, 2016
How would one calibrate such a machine sans a priori knowledge of the signal that they were looking for?

You check the background noise and see if all the signals you get can be explained by known processes.

They successfully discovered nothing! I can easily do that at a much lower cost.

No you can't. the trivial difference is:
They now KNOW that there is nothing in that energy range, whereas you could merely CLAIM that there is nothing within that energy range.

It's the difference between looking both ways and seeing that there are no cars coming
and
shutting your eyes, claiming that no cars are coming, and walking into the street.

One of those is sensible (and good science!)...the other is not.
Urgelt
4.4 / 5 (7) Jul 22, 2016
wkingmilw wrote, "No discussion of the recent hypothesis that dark matter consists of middle weight black holes surrounding galaxies. Oh well."

There isn't much new to discuss. WIMPs aren't ruled out; their possible characteristics have just been narrowed. Meanwhile physicists don't have a good theory handy to suggest why middle-weight black holes could exist in the numbers and locations required to account for observed gravitational effects. There would have to be a *lot* of them. All of them dark. No observable eating allowed. Not ruled out either, but it's looking like a stretch.

Perhaps just as likely are some new and exotic kind of singularity, maybe stuff produced during the Big Bang. Cosmic strings, or something. Who knows? We need observations.

That's what this article is about. Physicists are looking. They haven't found answers yet.
Benni
2.7 / 5 (7) Jul 22, 2016
The first helps to rule out some, not all, candidate explanations for dark matter effects seen in cosmological observations.


There are no DM effects seen in cosmological observations. It's all about a generation of aging Trekkies such as yourself, who have signed onto absolute foolishness & won't give it up since zany Zwicky concocted this slop-trough of cosmological swill in the 1930's against the advice of none other than Einstein himself.

You who has never worked as a science professional, are all into calling others "science deniers" just because your Trekkie dreams are beyond fulfillment. You sign onto narratives that imply Gravitational Lensing cannot occur anywhere in the Universe were it not for the presence of your favorite Cosmic Fairy Dust.

You're the "denier" when you cannot accept the fact that observations prove that the greatest gravitational effects are always found near giant Elliptical galaxy clusters, just where one would expect to see such effects.
Phys1
3.1 / 5 (10) Jul 22, 2016
The first helps to rule out some, not all, candidate explanations for dark matter effects seen in cosmological observations.


There are no DM effects seen in cosmological observations. It's all about a generation of aging Trekkies such as yourself, who have signed onto absolute foolishness & won't give it up since zany Zwicky concocted this slop-trough of cosmological swill in the 1930's against the advice of none other than Einstein himself.

You who has never worked as a science professional, are all into calling others "science deniers" just because your Trekkie dreams are beyond fulfillment. You sign onto narratives that imply Gravitational Lensing cannot occur anywhere in the Universe were it not for the presence of your favorite Cosmic Fairy Dust.

You are totally insane.
Phys1
2.9 / 5 (9) Jul 22, 2016
The new headline should read:

IT HAS BEEN DISCOVERED THAT MOST OF THE UNIVERSE IS NOT MISSING

Wow, Benni, the caps show so much confidence.
Mindless confidence, unfortunately.
Be careful, "novice", Benni is a nut case.
KBK
3.7 / 5 (3) Jul 22, 2016
So what has been eliminated? And more important, what remains?

From the abstract of this
https://arxiv.org...211.3788
The goal of the LUX detector is to clearly detect (or exclude) WIMPS with a spin independent cross section per nucleon of 2×10^−46 cm2


I.e. for WIMP theories stuff with a lower cross section remains.


One place to look for this sort of stuff is in the works of Gabriel Kron, who's works and math essentially disappeared into black ops from the mid 1950's and onward.

He put gravitational function and electrical motor anomalies in the same room, with fully functional math that is 100% engineerable and repeatable.

If one does not step out of mainstream science, they'll never find or know this sort of thing.

That in any long standing problem that cannot be solved, generally leads to the consideration of the question being the problem, the question being in error.
Benni
2.6 / 5 (8) Jul 22, 2016
That's what this article is about. Physicists are looking. They haven't found answers yet.


The article clearly states they have in fact "found answers". Did you even read it? It was clearly stated using the best detection instrumentation & data analyses that DM doesn't exist......here I'll quote it from the article because you are simply too lazy to read it:

LUX's sensitivity far exceeded the goals for the project, collaboration scientists said, but yielded no trace of a dark matter particle. LUX's extreme sensitivity makes the team confident that if dark matter particles had interacted with the LUX's xenon target, the detector would almost certainly have seen it.


There, get it? Probably not, you're just too much of a "science denier" incapable of a basic comprehension of nuclear physics.

bschott
2.5 / 5 (8) Jul 22, 2016
You are totally insane.

Wow, Benni, the caps show so much confidence.
Mindless confidence, unfortunately.
Be careful, "novice", Benni is a nut case.

Can somebody put this baby's soother back in his mouth so he stops annoying the adults with his random noise?
If you want to pretend to be a physicist, you should also try to pretend to understand physics and talk about it instead of wandering aimlessly around the site looking for people to try to annoy with your delinquent remarks and juvenile attitude. Or you can keep putting up posts demonstrating how useful your existence is...
epoxy
Jul 22, 2016
This comment has been removed by a moderator.
Phys1
2.9 / 5 (9) Jul 22, 2016
You are totally insane.

Wow, Benni, the caps show so much confidence.
Mindless confidence, unfortunately.
Be careful, "novice", Benni is a nut case.

Can somebody put this baby's soother back in his mouth so he stops annoying the adults with his random noise?
If you want to pretend to be a physicist, you should also try to pretend to understand physics and talk about it instead of wandering aimlessly around the site looking for people to try to annoy with your delinquent remarks and juvenile attitude. Or you can keep putting up posts demonstrating how useful your existence is...

You are overselling yourself.
You are still bschott, known for pushing bullshit and dirty talk.
Phys1
2.9 / 5 (9) Jul 22, 2016
For example in februari you wrote:
"I strongly advise you to change tampon brands, move out of moms house and find yourself a sexual companion that isn't already part of your physiology. "
This style of comment is your strong point.
Why don't you drop the science and concentrate on what you are good at?

Read more at: http://phys.org/n...nce.html
OdinsAcolyte
not rated yet Jul 25, 2016
One wonders if this is the wrong path.
I have always subscribed to the dark matter theory but I think we may be wrong. Back to the drawing board. Matter, Anti-matter, and....mmm...two more quadrants on the black board....
Watching with anticipation. It is a most interesting time to live.
OdinsAcolyte
4 / 5 (1) Jul 25, 2016
One wonders if this is the wrong path.
I have always subscribed to the dark matter theory but I think we may be wrong. Back to the drawing board. Matter, Anti-matter, and....mmm...two more quadrants on the black board....
Watching with anticipation. It is a most interesting time to live.

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