Posted on by Nancy Atkinson

No Joy for Dark Matter Detector’s First 100 Days

Bottom photomultiplier tube array on the XENON 100 detector. Credit: the XENON collaboration

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We’re still mostly in the dark about Dark Matter, and the highly anticipated results from the XENON100 detector has perhaps shed a tad more light on the subject – by not making a detection in the first 100 days of the experiment. Researchers from the project say they have now been able to place the most stringent limits yet on the properties of dark matter.

To look for any possible hints of Dark Matter interacting with ordinary matter, the project has been looking for WIMPS — or weakly interacting massive particles – but for now, there is no new evidence for the existence of WIMPS, or Dark Matter either.

The extremely sensitive XENON100 detector is buried beneath the Gran Sasso mountain in central Italy, shielding it from cosmic radiation so it hopefully can detect WIMPS, hypothetical particles that might be heavier than atomic nuclei, and the most popular candidate for what Dark Matter might be made of. The detector consists of 62 kg of liquid xenon contained within a heavily shielded tank. If a WIMP would enter the detector, it should interact with the xenon nuclei to generate light and electric signals – which would be a kind of “You Have Won!” indicator.

Dark Matter is thought to make up more than 80% of all mass in the universe, but the nature of it is still unknown. Scientists believe that it is made up of exotic particles unlike the normal (baryonic) matter, which we, the Earth, Sun and stars are made of, and it is invisible so it has only been inferred from its gravitational effects.

The XENON detector ran from January to June 2010 for its first run, and in their paper on arxiv, the team revealed they found three candidate events that might be due to Dark Matter. But two of these were expected to appear anyway because of background noise, the team said, so their results are effectively negative.

Does this rule out the existence of WIMPS? Not necessarily – the team will keep working on their search. Plus, results from a preliminary analysis from11.2 days worth of data, taken during the experiment’s commissioning phase in October and November 2009, already set new upper limits on the interaction rate of WIMPs – the world’s best for WIMP masses below about 80 times the mass of a proton.

And the XENON100 team was optimistic. “These new results reveal the highest sensitivity reported as yet by any dark matter experiment, while placing the strongest constraints on new physics models for particles of dark matter,” the team said in a statement.

Read the team’s paper.

More info on XENON100

Sources: EurekAlert, physicsworld

Posted on by Anne Minard

Perseus Cluster Thicker Around the Middle Than Thought

Credits: NASA/ISAS/DSS/A. Simionescu et al.; inset: NASA/CXC/A. Fabian et al.

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The Japanese Suzaku X-ray telescope has just taken a close look at the Perseus galaxy cluster, and revealed it’s got a bit of a spare tire.

Suzaku explored faint X-ray emission of hot gas across two swaths of the Perseus Galaxy Cluster. The resulting images, which record X-rays with energies between 700 and 7,000 electron volts in a combined exposure of three days, are shown in the two false-color strips above. Bluer colors indicate less intense X-ray emission. The dashed circle is 11.6 million light-years across and marks the so-called virial radius, where cold gas is now entering the cluster. Red circles indicate X-ray sources not associated with the cluster.

The results appear in today’s issue of Science.

The Perseus cluster (03hh 18m +41° 30‘) is the brightest extragalactic source of extended X-rays.

Lead author Aurora Simionescu, an astrophysicist at Stanford, and her colleagues note that until now, most observations of galaxy clusters have focused on their bright interiors. The Suzaku telescope was able to peer more closely at the outskirts of the Perseus cluster. The resulting census of baryonic matter (protons and neutrons of gas and metals) compared to dark matter offers some surprising observations.

It turns out the fraction of baryonic matter to dark matter at Perseus’s center was consistent with measurements for the universe as a whole, but the baryonic fraction unexpectedly exceeds the universal average on the cluster’s outskirts.

“The apparent baryon fraction exceeds the cosmic mean at larger radii, suggesting a clumpy distribution of the gas, which is important for understanding the ongoing growth of clusters from the surrounding cosmic web,” the authors write in the new paper.

Source: Science. See also JAXA’s Suzaku site

Posted on by Nancy Atkinson

Hunt for Dark Matter Closes in at the LHC

The Large Hadron Collider’s Compact Muon Solenoid (CMS) detector. Credit: CMS Collaboration/CERN

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From an Imperial College London press release:

Physicists say they are closer than ever to finding the source of the Universe’s mysterious dark matter, following a better than expected year of research at the Compact Muon Solenoid (CMS) particle detector, part of the Large Hadron Collider (LHC) at CERN in Geneva.

The scientists have now carried out the first full run of experiments that smash protons together at almost the speed of light. When these sub-atomic particles collide at the heart of the CMS detector, the resultant energies and densities are similar to those that were present in the first instants of the Universe, immediately after the Big Bang some 13.7 billion years ago. The unique conditions created by these collisions can lead to the production of new particles that would have existed in those early instants and have since disappeared.

The researchers say they are well on their way to being able to either confirm or rule out one of the primary theories that could solve many of the outstanding questions of particle physics, known as Supersymmetry (SUSY). Many hope it could be a valid extension for the Standard Model of particle physics, which describes the interactions of known subatomic particles with astonishing precision but fails to incorporate general relativity, dark matter and dark energy.

In particle physics, supersymmetry is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known assuperpartners. In a theory with unbroken supersymmetry, for every type of boson there exists a corresponding type of fermion with the same mass and internal quantum numbers, and vice-versa.

Dark matter is an invisible substance that we cannot detect directly but whose presence is inferred from the rotation of galaxies. Physicists believe that it makes up about a quarter of the mass of the Universe whilst the ordinary and visible matter only makes up about 5% of the mass of the Universe. Its composition is a mystery, leading to intriguing possibilities of hitherto undiscovered physics.

Professor Geoff Hall from the Department of Physics at Imperial College London, who works on the CMS experiment, said, “We have made an important step forward in the hunt for dark matter, although no discovery has yet been made. These results have come faster than we expected because the LHC and CMS ran better last year than we dared hope and we are now very optimistic about the prospects of pinning down Supersymmetry in the next few years.”

The energy released in proton-proton collisions in CMS manifests itself as particles that fly away in all directions. Most collisions produce known particles but, on rare occasions, new ones may be produced, including those predicted by SUSY – known as supersymmetric particles, or ‘sparticles’. The lightest sparticle is a natural candidate for dark matter as it is stable and CMS would only ‘see’ these objects through an absence of their signal in the detector, leading to an imbalance of energy and momentum.

In order to search for sparticles, CMS looks for collisions that produce two or more high-energy ‘jets’ (bunches of particles traveling in approximately the same direction) and significant missing energy.

Dr. Oliver Buchmueller, also from the Department of Physics at Imperial College London, but who is based at CERN, said, “We need a good understanding of the ordinary collisions so that we can recognise the unusual ones when they happen. Such collisions are rare but can be produced by known physics. We examined some 3 trillion proton-proton collisions and found 13 ‘SUSY-like’ ones, around the number that we expected. Although no evidence for sparticles was found, this measurement narrows down the area for the search for dark matter significantly.”

The physicists are now looking forward to the 2011 run of the LHC and CMS, which is expected to bring in data that could confirm Supersymmetry as an explanation for dark matter.

The CMS experiment is one of two general purpose experiments designed to collect data from the LHC, along with ATLAS (A Toroidal LHC ApparatuS). Imperial’s High Energy Physics Group has played a major role in the design and construction of CMS and now many of the members are working on the mission to find new particles, including the elusive Higgs boson particle (if it exists), and solve some of the mysteries of nature, such as where mass comes from, why there is no anti-matter in our Universe and whether there are more than three spatial dimensions.

Posted on by Mark Thompson

Red Dwarf Discovery Changes Everything!

Artists Impression of a Red Dwarf (courtesy NASA)

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Its often said that the number of grains of sand on Earth equals the number of stars in the Universe. Well it looks like a recent study by astronomers working at the Keck Observatory in Hawaii have found that its more like three times the number of grains of sand on Earth! Working with some of the most sophisticated equipment available, astronomers from Yale University have been counting the number of dim red dwarf stars in nearby galaxies which has led to a dramatic rethink of the number of stars in the Universe.

Red dwarfs are small, faint stars compared to most others and until now, have not been detected in nearby galaxies. Pieter van Dokkum and his team from Yale University studied eight massive elliptical galaxies between 50 and 300 million lights years from us and discovered that these tiny stars are much more bountiful than first thought. “No one knew how many of these stars there were,” said Van Dokkum. “Different theoretical models predicted a wide range of possibilities, so this answers a long standing question about just how abundant these stars are.”

For years astronomers have assumed that the number of red dwarfs in any galaxy was in the same proportion that we find here in the Milky Way but surprisingly the study revealed there are about 20 times more in the target galaxies. According to Charlie Conroy of the Harvard-Smithsonian Center who also worked on the project, “not only does this affect our understanding of the number of stars in the Universe but the discovery could have a major impact on our understanding of galaxy formation and evolution.” Knowing that there are now more stars than previously thought, this lowers the amount of dark matter (a mysterious substance that cannot be directly observed but its presence inferred from its gravitational influence) needed to explain the observed gravitational influence on surrounding space.

Not only has the discovery affected the amount of dark matter we expect to find but it also changes the quantity of planets that may exist in the Universe. Planets have recently been discovered orbiting around other red dwarf stars such as the system orbiting around Gliese 581, one which may harbour life. Now that we know there are a significantly higher number of red dwarfs in the Universe, the potential number of planets in the Universe has increased too. Van Dookum explains “There are possibly trillions of Earth’s orbiting these stars, since the red dwarfs they have discovered are typically more than 10 billion years old, so have been around long enough for complex life to evolve, its one reason why people are interested in this type of star.”

It seems then that this discovery, which on the face of it seems quite humdrum, actually has far reaching consequences that not only affect our view of the number of stars in the Universe but has dramatically changed our understanding of the distribution of matter in the Universe and the number of planets that may harbour intelligent life.

The new findings appear in the Dec. 1st online issue of the journal Nature.

Source: from the Harvard Smithsonian Center for Astrophysics.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Posted on by Jon Voisey

Missing Milky Way Dark Matter

A composite image shows a dark matter disk in red. From images in the Two Micron All Sky Survey. Credit: Credit: J. Read & O. Agertz.

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Although dark matter is inherently difficult to observe, an understanding of its properties (even if not its nature) allows astronomers to predict where its effects should be felt. The current understanding is that dark matter helped form the first galaxies by providing gravitational scaffolding in the early universe. These galaxies were small and collapsed to form the larger galaxies we see today. As galaxies grew large enough to shred incoming satellites and their dark matter, much of the dark matter should have been deposited in a flat structure in spiral galaxies which would allow such galaxies to form dark components similar to the disk and halo. However, a new study aimed at detecting the Milky Way’s dark disk have come up empty.


The study concentrated on detecting the dark matter by studying the luminous matter embedded in it in much the same way dark matter was originally discovered. By studying the kinematics of the matter, it would allow astronomers to determine the overall mass present that would dictate the movement. That observed mass could then be compared to the amount of mass predicted of both baryonic matter as well as the dark matter component.

The team, led by C. Moni Bidin used ~300 red giant stars in the Milky Way’s thick disk to map the mass distribution of the region. To eliminate any contamination from the thin disc component, the team limited their selections to stars over 2 kiloparsecs from the galactic midplane and velocities characteristic of such stars to avoid contamination from halo stars. Once stars were selected, the team analyzed the overall velocity of the stars as a function of distance from the galactic center which would give an understanding of the mass interior to their orbits.

Using estimations on the mass from the visible stars and the interstellar medium, the team compared this visible mass to the solution for mass from the observations of the kinematics to search for a discrepancy indicative of dark matter. When the comparison was made, the team discovered that, “[t]he agreement between the visible mass and our dynamical solution is striking, and there is no need to invoke any dark component.”

While this finding doesn’t rule out the presence of dark matter, it does place constraints on it distribution and, if confirmed in other galaxies, may challenge the understanding of how dark matter serves to form galaxies. If dark matter is still present, this study has demonstrated that it is more diffuse than previously recognized or perhaps the disc component is flatter than previously expected and limited to the thin disc. Further observations and modeling will undoubtedly be necessary.

Yet while the research may show a lack of our understanding of dark matter, the team also notes that it is even more devastating for dark matter’s largest rival. While dark matter may yet hide within the error bars in this study, the findings directly contradict the predictions of Modified Newtonian Dynamics (MOND). This hypothesis predicts the apparent gain of mass due to a scaling effect on gravity itself and would have required that the supposed mass at the scales observed be 60% higher than indicated by this study. Continue reading “Missing Milky Way Dark Matter”

Posted on by Nancy Atkinson

Astronomers Find Black Holes Do Not Absorb Dark Matter

Artist’s schematic impression of the distortion of spacetime by a supermassive black hole at the centre of a galaxy. The black hole will swallow dark matter at a rate which depends on its mass and on the amount of dark matter around it. Image: Felipe Esquivel Reed.

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There’s the common notion that black holes suck in everything in the nearby vicinity by exerting a strong gravitational influence on the matter, energy, and space surrounding them. But astronomers have found that the dark matter around black holes might be a different story. Somehow dark matter resists ‘assimilation’ into a black hole.

About 23% of the Universe is made up of mysterious dark matter, invisible material only detected through its gravitational influence on its surroundings. In the early Universe clumps of dark matter are thought to have attracted gas, which then coalesced into stars that eventually assembled the galaxies we see today. In their efforts to understand galaxy formation and evolution, astronomers have spent a good deal of time attempting to simulate the build up of dark matter in these objects.

Dr. Xavier Hernandez and Dr. William Lee from the National Autonomous University of Mexico (UNAM) calculated the way in which the black holes found at the center of galaxies absorb dark matter. These black holes have anything between millions and billions of times the mass of the Sun and draw in material at a high rate.

The researchers modeled the way in which the dark matter is absorbed by black holes and found that the rate at which this happens is very sensitive to the amount of dark matter found in the black holes’ vicinity. If this concentration were larger than a critical density of 7 Suns of matter spread over each cubic light year of space, the black hole mass would increase so rapidly, hence engulfing such large amounts of dark matter, that soon the entire galaxy would be altered beyond recognition.

“Over the billions of years since galaxies formed, such runaway absorption of dark matter in black holes would have altered the population of galaxies away from what we actually observe,” said Hernandez

Their work therefore suggests that the density of dark matter in the centers of galaxies tends to be a constant value. By comparing their observations to what current models of the evolution of the Universe predict, Hernandez and Lee conclude that it is probably necessary to change some of the assumptions that underpin these models – dark matter may not behave in the way scientists thought it did.

There work appears in the journal Monthly Notices of the Royal Astronomical Society.

The team’s paper can be found here.

Posted on by Steve Nerlich

What Can The (Dark) Matter Be?

What better place to look for dark matter than down a mine shaft? A research team from the University of Florida have spent nine years monitoring for any signs of the elusive stuff using germanium and silicon detectors cooled down to a fraction of a degree above absolute zero. And the result? A couple of maybes and a gritty determination to keep looking. 

The case for dark matter can be appreciated by considering the solar system where, to stay in orbit around the Sun, Mercury has to move at 48 kilometers a second, while distant Neptune can move at a leisurely 5 kilometers a second. Surprisingly, this principle doesn’t apply in the Milky Way or in other galaxies we have observed.  Broadly speaking, you can find stuff in the outer parts of a spiral galaxy that is moving just as fast as stuff that is close in to the galactic centre. This is puzzling, particularly since there doesn’t seem to be enough gravity in the system to hold onto the rapidly orbiting stuff in the outer parts – which should just fly off into space. 

So, we need more gravity to explain how galaxies rotate and stay together – which means we need more mass than we can observe – and this is why we invoke dark matter. Invoking dark matter also helps to explain why galaxy clusters stay together and explains large scale gravitational lensing effects, such as can be seen in the Bullet Cluster (pictured above). 

Computer modeling suggests that galaxies may have dark matter halos, but they also have dark matter distributed throughout their structure – and taken together, all this dark matter represents up to 90% of a galaxy’s total mass. 

An artist's impression of dark matter, showing the proportional distribution of baryonic and non-baryonic forms (this joke never gets old).

Current thinking is that a small component of dark matter is baryonic, meaning stuff that is composed of protons and neutrons – in the form of cold gas as well as dense, non-radiant objects such black holes, neutron stars, brown dwarfs and orphaned planets (traditionally known as Massive Astrophysical Compact Halo Objects – or MACHOs). 

But it doesn’t seem that there is nearly enough dark baryonic matter to account for the circumstantial effects of dark matter. Hence the conclusion that most dark matter must be non-baryonic, in the form of Weakly Interacting Massive Particles (or WIMPs). 

By inference, WIMPS are transparent and non-reflective at all wavelengths and probably don’t carry a charge. Neutrinos, which are produced in abundance from the fusion reactions of stars, would fit the bill nicely except they don’t have enough mass. The currently most favored WIMP candidate is a neutralino, a hypothetical particle predicted by supersymmetry theory. 

The second Cryogenic Dark Matter Search Experiment (or CDMS II) runs deep underground in the Soudan iron mine in Minnesota, situated there so it should only intercept particles that can penetrate that deeply underground. The CDMS II solid crystal detectors seek ionization and phonon events which can be used to distinguish between electron interactions – and nuclear interactions. It is assumed that a dark matter WIMP particle will ignore electrons, but potentially interact with (i.e. bounce off) a nucleus. 

Two possible events have been reported  by the University of Florida team, who acknowledge their findings cannot be considered statistically significant, but may at least give some scope and direction to further research.

By indicating just how difficult to directly detect (i.e. just how ‘dark’) WIMPs really are – the CDMS II findings indicate the sensitivity of the detectors needs to bumped up a notch.

Posted on by Nancy Atkinson

Dark Matter Detector Heading to the ISS This Summer

AMS-2 during integration activities at CERN facility in Switzerland. Credit: ESA

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The long-awaited experiment that will search for dark matter is getting closer to heading to the International Space Station. The Alpha Magnetic Spectrometer (AMS) is undergoing final testing at ESA’s Test Centre in the Netherlands before being launched on the space shuttle to the ISS, currently scheduled for July, 2010. The AMS will help scientists better understand the fundamental issues on the origin and structure of the Universe by observing dark matter, missing matter and antimatter. As a byproduct, AMS will gather other information from cosmic radiation sources such as stars and galaxies millions of light years from our home galaxy.

ISS officials have been touting that science is now beginning to be done in earnest on the orbiting laboratory. The AMS will be a giant leap in science capability for the ISS. Not only is it the biggest scientific instrument to be installed on the International Space Station (ISS), but also it is the first magnetic spectrometer to be flown in space, and the largest cryogenically cooled superconducting magnet ever used in space. It will be installed on the central truss of the ISS.
Location of where the AMS will be located on the exterior of the ISS. Credits: CERN et Universite de Geneve
AMS had been cut from the ISS program following the 2003 Columbia shuttle accident, but the outcry over the cancellation forced NASA to rethink their decision. Most of AMS’s $1.5-billion costs have been picked up the international partners that NASA wishes to stay on good terms with. 56 institutes from 16 countries have contributed to the AMS project, with Nobel laureate Samuel Ting coordinating the effort.

In an interview with the BBC, Ting said results from AMS may take up to three years to search for antimatter in other galaxies, and dark matter in our own.
The instrument was built at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland. The first part of the tests was also conducted at CERN, when the detector was put through its paces using a proton beam from CERN’s Super Proton Synchrotron accelerator to check its momentum resolution and its ability to measure particle curvature and momentum.

AMS’s ability to distinguish electrons from protons was also tested. This is very important for the measurement of cosmic rays, 90% of which are protons and constitute a natural background for other signals that interest scientists. AMS will be looking for an abundance of positrons and electrons from space, one of the possible markers for dark matter.

Once the extensive testing is complete, AMS will leave ESTEC at the end of May on a special US Air Force flight to Kennedy Space Center in Florida. It will be launched to the ISS on the Space Shuttle Endeavour on flight STS-134, now scheduled for July.

Source: ESA

Posted on by Ryan Anderson

Milky Way Has a “Squashed Beachball”-Shaped Dark Matter Halo

This illustration shows the visible Milky Way galaxy surrounded by a "squashed beachball"-shaped dark matter halo. Source: UCLA

This illustration shows the visible Milky Way galaxy surrounded by a “squashed beachball”-shaped dark matter halo. Source: UCLA

Our galaxy is shaped like a flat spiral right? Not if you’re talking about dark matter. Astronomers announced today that the Milky Way’s dark matter halo, which represents about 70% of the galaxy’s mass, is actually shaped like a squashed beachball.

Dark matter is completely invisible, but it still obeys the law of gravity, so the existence of dark matter haloes, and their shape, can be inferred by monitoring the orbits of dwarf galaxies orbiting the much larger Milky Way.

Unfortunately, to determine the orbit of an object, you have to measure its position at several points in that orbit, and dwarf galaxies take about a billion years to go around the Milky Way. Astronomers just haven’t been around long enough to watch even a fraction of a complete orbit. Luckily, they don’t have to.

Dwarf galaxies, just like their full-sized counterparts, and made of billions of stars. When the tidal forces from a big galaxy like the Milky Way act on a dwarf galaxy, the result is a streamer of stars that trace out the dwarf galaxy’s orbit. By using data from huge all-sky surveys, a group of astronomers led by David Law at UCLA were able to reconstruct the orbit of the Sagittarius Dwarf Galaxy. There was just one problem: different parts of the dwarf galaxy had different orbits, which led to wildly different dark matter halo shapes.

Law and his colleagues Steven Majewski (University of Virginia) and Kathryn Johnston (Columbia University) solved this problem by allowing models of the dark matter halo to be “triaxial” – in other words, have different lengths in all three dimensions. The best model solution results in a halo shaped like a beach ball that has been squashed sideways.

“We expected some amount of flattening based on the predictions of the best dark-matter theories,” said Law, “but the extent, and particularly the orientation, of the flattening was quite unexpected. We’re pretty excited about this, because it begs the question of how our galaxy formed in its present orientation.”

Sagittarius is not the only dwarf galaxy orbiting the Milky Way, and Law and his colleagues plan to study the orbits of other dwarf galaxies to refine their model. “It will be important to see if these results hold up as precise orbits are measured for more of these galaxies. In the meantime, such a squashed dark-matter halo is one of the best explanations for the observed data.”

This illustration shows the visible Milky Way galaxy (blue spiral) and the streams of stars represent the tidally shredded Sagittarius dwarf galaxy. Click the image for a flyaround view. Source: UCLA

This illustration shows the visible Milky Way galaxy (blue spiral) and the streams of stars represent the tidally shredded Sagittarius dwarf galaxy. Source: UCLA

Posted on by Jon Voisey

New Results from the CDMS II Experiment

It’s no secret that astronomers claim that most of our universe is made of dark matter that cannot be readily detected. From Fritz Zwicky’s observations of the Coma clusters in the 1920’s which suggested that additional mass would be necessary to hold the cluster together, to the flat rotation curves of galaxies, to lensing in such places as the Bullet Cluster, all signs point to matter that neither emits nor absorbs any form of light we can detect. One possible solution was that this missing matter was ordinary, but cold matter floating around the universe. This form was called Massive astrophysical compact halo objects, or MACHOs, but studies to look for these came up relatively empty. The other option was that this dark matter was not so garden variety. It posed the idea of hypothetical particles which were very massive, but would only rarely interact. These particles were nicknamed WIMPs (for weakly interacting massive particles). But if these particles were so weakly interacting, detecting them would be a challenge.

An ambitious project, known as the Cryogenic Dark Matter Search, has been attempting to detect one of these particles since 2003. Today, they made a major announcement.

The experiment is located a half-mile underground in the Soudan mine in northern Minnesota. The detector is kept here to shield it from cosmic rays. The detectors are made from germanium and silicon which, if struck by a potential WIMP, will become ionized and resonate. The combination of these two features allow for the team to gain some insight as to what sort of particle it was that triggered the event. To further weed out false detections, the detectors are all cooled to just above absolute zero which prevents most of the “noise” caused by the random jittering of atoms thanks to their temperature.

Although the detector had not previously found signs for any dark matter they have provided understanding of the background levels to the degree that the team felt confident that they would be able to begin distinguishing true events. Despite this, false positives from neutron collisions have required the team to “throw out roughly 2/3 of the data that might contain WIMPs, because these data would contain too many background events.”

The most recent review of the data covered the 2007-2008 set. After carefully cleaning the data of as many false events and as much background noise as possible the team discovered that two detection events remained. The significance of these two detections was the result of today’s conference.

Although the presence of these two detections from 8/5 and 10/27 2007, could not be ruled out as genuine dark matter detections, the presence of only two detections was not statistically significant enough to be able to truly stand out from the background noise. As the summary of results from the team described it, “Typically there must be less than one chance in a thousand of the signal being due to background. In this case, a signal of about 5 events would have met those criteria.” As such, there is only a 1:4 probability that this was a true case of a detection of WIMPs.

Astronomer turned writer, Phil Plait put it slightly more succinctly in a tweet; “The CDMS dark matter talk indicates two signals, but they are not statistically strong enough to say “here be dark matter”. Damn.”

For more information:

Collaboration’s Website

Liveblogging of Conference by Cosmic Variance