New data from XENON100 narrows the possible range for dark matter

New data from XENON100 narrows the possible range for dark matter
1) The surface of the Earth is constantly bombarded by cosmic radiation. Only the most energetic particles penetrate the rock, so detectors aiming to "see" the rare signal from cosmic Dark Matter are placed beneath the Earth. 2) Dark Matter in the form of Weakly Interacting Massive Particles (WIMPs) can traverse the Earth without interacting with it to reach XENON100, a detector filled with liquid xenon that is designed to be sensitive to such rare encounters. 3) A WIMP interaction in the liquid xenon will excite atoms and free electrons, which will be picked up again swiftly by the atoms. Both processes produce a flash of light that can be detected by photomultipliers, which act as extremely sensitive cameras, at each end of the tank. 4) An electric field running through the detector prevents some of the electrons from recombining with the xenon atoms. These free electrons are pushed upwards towards the anode, an electrode through which electric current flows, until they reach the liquid-to-gas interface. 5) At the interface, a stronger electric field pulls the electrons out of the liquid into the gas, where they create another flash of light that is detected by the same photomultipliers. The brightness of this second flash compared with the first one reveals the type of particle that caused the signal.Credit: Zina Deretsky, National Science Foundation
(PhysOrg.com) -- An International team of scientists in the XENON collaboration, including several from the Weizmann Institute, announced on Thursday the results of their search for the elusive component of our universe known as dark matter. This search was conducted with greater sensitivity than ever before. After one hundred days of data collection in the XENON100 experiment, carried out deep underground at the Gran Sasso National Laboratory of the INFN, in Italy, they found no evidence for the existence of Weakly Interacting Massive Particles – or WIMPs – the leading candidates for the mysterious dark matter. The three candidate events they observed were consistent with two they expected to see from background radiation. 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. Weizmann Institute professors Eilam Gross, Ehud Duchovni and Amos Breskin, and the research student Ofer Vitells, made significant contributions to the findings by introducing a new statistical method that both increases the search sensitivity and enables new discovery.

Any direct observation of WIMP activity would link the largest observed structures in the with the world of subatomic particle physics. While such detection cannot be claimed as yet, the level of sensitivity achieved by the XENON100 experiment could be high enough to allow an actual detection in the near future. What sets XENON100 apart from competing experiments is its significantly lower background radiation The XENON100 detector, which uses 62 kg of as its WIMP target, and which measures tiny charges and light signals produced by predicted rare collisions between WIMPs and xenon atoms, continues its search for WIMPs. New data from the 2011 run, as well as the plan to build a much larger experiment in the coming years, promise an exciting decade in the search for the solution to one of nature's most fundamental mysteries.


Dark matter has so far foiled most means of detection, but researchers are continuing to pursue its mysteries. They're using the most sensitive detector yet, called Xenon100, to try to glimpse the particles. See how it works in this video. Credit: National Science Foundation

Cosmological observations consistently point to a picture of our universe in which the ordinary matter we know makes up only 17% of all matter; the rest – 83% – is in an as yet unobserved form – so-called dark matter. This complies with predictions of the smallest scales; necessary extensions of the Standard Model of particle physics suggest that exotic new particles exist, and these are perfect dark matter candidates. Weakly Interacting (WIMPs) are thus implied in both cosmology and particle physics. An additional hint for their existence lies in the fact that the calculated abundance of such particles arising from the Big Bang matches the required amount of dark matter. The search for WIMPs is thus well-founded; a direct detection of such particles would provide the central missing piece needed to confirm this new picture of our Universe.

The properties of dark matter have been addressed through a variety of approaches and methods; these have provided the scientists with indirect hints of what to search for. WIMPs are expected to have a mass comparable to that of atomic nuclei, with a very low probability of interacting with normal matter. Such particles are thought be distributed in an enormous cloud surrounding the visible disk of the Milky Way. Earth is moving through this cloud, along with the Sun, on its journey around the Galaxy center. This movement results in a 'WIMP wind,' which may occasionally scatter off atomic nuclei in an Earth-bound detector, releasing a tiny amount of energy, which can then be detected with ultra- sensitive devices.

In the XENON100 experiment, 62 kg of liquid xenon acts as a WIMP target. The liquid, at a temperature of about -90° C, is contained in a stainless steel cryostat equipped with a cryo-cooler to maintain highly stable operating conditions. The experiment is located in the Gran Sasso Underground Laboratory (LNGS) in Italy where it is shielded from cosmic radiation by 1400 meters of rock. Further shielding from radioactivity in the detector itself and its surroundings is provided by layers of active and passive absorbers surrounding the target. These include 100 kg of active liquid xenon scintillator, 2 tons of ultra-pure copper, 1.6 tons of polyethylene and 34 tons of lead and water. The radio-pure materials used to produce the detector components assure an ultra-low background radiation environment.

Particles interacting within the active liquid xenon space excite and ionize atoms. This results in light emission in the deep ultraviolet. As electrons drift across the liquid xenon, they create a delayed, luminescent signal on the top of the detector, due to the experiment's strong electric field. Both primary and secondary scintillation light signals are detected via two arrays of photosensors – one located in the liquid xenon at the bottom, and one in the gas above the liquid (Figure 1). The simultaneous measurement of these two light signals enables the researchers to infer both the energy and the spatial coordinates of the particles' interaction, while providing information on their nature. This analysis of ratio of the two light signals and their precise localization in space is an extremely accurate method of distinguishing WIMP signals from background events.

Many of technologies and methods used in the XENON100 experiment have been built on the research and development efforts of the XENON Dark Matter Search program, which produced, in 2006, the XENON10 prototype. For XENON100, a ten-fold increase in fiducial target mass, combined with 100-fold reduction in background, translates into a substantial improvement in sensitivity to WIMP-nucleon elastic scattering. An extensive calibration using various sources of gammas and neutrons was performed to demonstrate that XENON100 reached its goals for sensitivity and for low background radiation.

Results from a preliminary analysis from11.2 days worth of data, taken during the experiment's commissioning phase in October and November 2009, have 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 ( Physical Review Letters 105 (2010) 131302).

A new dark matter search was performed between January and June, 2010, and 100 days worth of data from this run have been analyzed. Three candidate events were found within the pre-defined parameters in which the WIMP signal is expected to appear. However, these events, while coming from true particle interactions in the detector, are consistent with predictions of two such events resulting from radioactive backgrounds. Thus evidence for dark matter cannot be claimed, but a new upper limit for the strength of its interaction with normal matter could be calculated. These results represent the best limits to date. They narrow the possibilities open to supersymmetric particle physics theories that predict the nature of dark matter.

XENON100 has achieved the lowest background among all dark matter experiments worldwide (Physical Review D (2011), arXiv:1101.3866). Since the data presented here were collected, the intrinsic background from radioactive krypton in the xenon filling XENON100 has been reduced to an unprecedented low level and the detectors' performance has been improved as well. Even as new data are being collected in these improved conditions, the scientific team is preparing a next-generation search experiment featuring a detector that will contain more than 1000 kg of liquid as a fiducial WIMP target. With further reduction in overall background radiation, XENON1T promises to be a hundred times more sensitive than XENON100.


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Highly Sensitive Dark Matter Experiment Disproves Earlier Findings

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Apr 14, 2011
"We found absolutely NOTHING! Send ten times more money please!"

Apr 14, 2011
Dark matter is like Count Dracula. It will take more than a few nails in the coffin to put this 70 year-old, reflexive, neo-aether notion to rest. Fortunately, there are now three studies linking the temperature of a test mass to its weight. These studies open up the never-thought-of but almost-obvious possibility that luminosity is the source of gravitational attraction. Luminosity is ubiquitous. It emanates from all gravitationally bound bodies in the universe.

http://arxiv.org/abs/0803.1730
http://vixra.org/abs/0907.0018
http://www.screen...c7c8f5e1

Apr 14, 2011
This comment has been removed by a moderator.

Apr 14, 2011
This comment has been removed by a moderator.

Apr 14, 2011
Could it be that the Local Bubble we're currently passing through is bereft of the stuff ?? http://en.wikiped...l_Bubble

Apr 14, 2011
They're still looking in the wrong place

http://www.presto...ndex.htm

Apr 14, 2011
No surprise there!

ZephirAWT:
Good thinking out of the box; however, we call what you are referring to...the energy of the curvature of space as gravity or gravitative attraction.

I think I see where you are going with this but it needs some refining i.e. curvature energy is how the mass expresses its attraction; and if there were more mass attributed to curved space due to its curvature energy, besides the mass curving the space itself, we would most likely observer it especially for a local body like the Sun or moon but I like your thinking.


Apr 14, 2011
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Apr 14, 2011
Dark matter is hyperdimensional effect, it's observable only from sufficient distance of massive body .

I couldnt disagree more!

Id like to formalize the model here particularly since you brought up the Pioneer anomaly which I have been studying for some time, but this is not the time or place. I do think we will soon discover that what we call Dark Matter is intrinsic to all matter local or non-local and is not mediated by a particle(s).

Apr 14, 2011
@Zephir
As I understand it, it's negligible for weak field, and already incorporated in Einstein's equations given non-linear solutions, and so is considered as space-time curvature in strong field. No reason to consider as "additional mass".

Apr 14, 2011
This comment has been removed by a moderator.

Apr 14, 2011
This comment has been removed by a moderator.

Apr 14, 2011
I think it (Dark Matter) has to do with a fundamental difference between inertial and gravitational mass as it relates to its position vector, of the test mass, within the curvature of a larger body, for example.

And more...

Apr 14, 2011
The XENON100 detector experiment is brilliant, however we (humans) are about to confirm that the anti-matter created at the time of the big bang (and the big bang will soon be disproven in it's curent state) is an inverse of matter which has a repulsive force gravitationally (anti gravity). Relativity mathematically proves this repulsion, but makes for a tough experiment. nonetheless, these particles did not annihilate at the time of the "bang" but instead move apart at an ever increasing rate. this phenomenon will explain dark matter & dark energy in the near future when they finally experimentally test matter & anti matter's gravitational effects on each other. We're unfortunately wrong on WIMPS and MACHOS. Looking for things that don't exist make them tough to find.

Apr 14, 2011
Good luck with that!

Apr 14, 2011
"We found absolutely NOTHING! Send ten times more money please!"

You do understand that in science negative results can be as significant as positive ones? This is true in the same sense as when you looking for something. If you completely clean 3 rooms and verify absolutely that the missing thing is not in those rooms, you have narrowed your search to the rest of the house (analogous in this case to eliminating energies and types of particles corresponding to Dark Matter particles), or in fact completely outside the house (oops we better question more seriously the existence of dark matter at all).

Apr 14, 2011
Y'all (You all) are so impatient! Dark Matter is.... (duh)Dark. As in: very hard to find. Until we allow for some serious time interval (after all, this is a serious matter), we won't have enough evidence to determine -- beyond a reasonable doubt -- whether DM exists or not. Until then, I'm agnostic on this issue.

Apr 14, 2011
In all research fields, current team based science is chocked with near retired senior scientists whose main focus has been to accept fashionable mainstream theories where the premise foundations for scientific argument are popular held beliefs based upon a system that perpetuates the closed minded certitude of the very few that impresses their way of thinking upon the many for a fleeting contemporary financial gain.

With this type of scientific system in place what do you think would happen if some lowly grad student from some backwater college or university came up with an elegant proof or some strong scientific results that completely dismissed the possibility dark matter existing altogether?

What do you think the senior scientist that just invested 8 years of his life and spent 230 million government dollars to build an advanced Dark Matter detection instrument in Antarctica would say?

Welcome to modern scientific thinking and research 2011!

Apr 14, 2011
I think this search is very important to prove/disprove DM as a WIMP. That said, the following sentence made me laugh...

"New data from the 2011 run, as well as the plan to build a much larger experiment in the coming years, promise an exciting decade in the search for the solution to one of nature's most fundamental mysteries."

Really? You consider sitting in a cave for 10 years doing nothing 99.99% of the time "exciting"?

Apr 14, 2011

That aside, given the recent 3 Sigma results at the CDF, perhaps these searches should begin to expand and look for technicolor DM candidates.

Apr 14, 2011
Why so exotic of ideas for DM before standard candidate mechanisms havent been fully explored or even discussed?

If DM exists, it's something fundamental and we can't see it directly perhaps because of our reference position within the curvature metric of the Earth...kind of like a quantum decoherence of phased space-time.

As long as we think that DM is something that can't be found without large amounts of cash and huge powerful instruments we will be null-ing our way through much of the SM universe.

yep
Apr 15, 2011
No need for dark matter with an electric universe

Apr 17, 2011
they didn't find jack s***, 62 kg xenon is a pretty small cross-section, but given the sheer amount of shielding and money, needed to enclose this target, you don't start out with 1000 kg xenon and 10.000 tons of ultra pure copper, you do the small thing first and hope you get lucky, they did'nt strike gold, but at least validated many aspects of the searchmethod, wich i think is good enough to give them more candy for another go.

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