A silent search for dark matter

August 22, 2017, Rensselaer Polytechnic Institute
The world's most sensitive dark matter detector demonstrates record low radioactivity levels. Credit: XENON Collaboration

Results from its first run indicate that XENON1T is the most sensitive dark matter detector on Earth. The sensitivity of the detector—an underground sentinel awaiting a collision that would confirm a hypothesis—stems from both its size and its "silence." Shielded by rock and water, and purified with a sophisticated system, the detector demonstrated a new record low radioactivity level, many orders of magnitude below surrounding material on Earth.

"We are seeing very good quality data from this detector, which tells us that it is running perfectly," said Ethan Brown, a XENON1T Collaboration member, and assistant professor of physics, applied physics, and astronomy at Rensselaer Polytechnic Institute.

Dark matter is theorized as one of the basic constituents of the universe, five times more abundant than ordinary matter. But because it cannot be seen and seldom interacts with ordinary matter, its existence has never been confirmed. Several astronomical measurements have corroborated the existence of , leading to a worldwide effort to directly observe dark matter particle interactions with . Up to the present, the interactions have proven so feeble that they have escaped direct detection, forcing scientists to build ever-more-sensitive detectors.

Since 2006, the XENON Collaboration has operated three successively more sensitive liquid xenon detectors in the Gran Sasso Underground Laboratory (LNGS) in Italy, and XENON1T is its most powerful venture to date and the largest detector of its type ever built. Particle interactions in create tiny flashes of light, and the detector is intended to capture the flash from the rare occasion in which a dark matter particle collides with a xenon nucleus.

But other interactions are far more common. To shield the detector as much as possible from natural radioactivity in the cavern, the detector (a so-called Liquid Xenon Time Projection Chamber) sits within a cryostat submersed in a tank of water. A mountain above the underground laboratory further shields the detector from cosmic rays. Even with shielding from the outside world, contaminants seep into the xenon from the materials used in the detector. Among his contributions, Brown is responsible for a purification system that continually scrubs the xenon in the detector.

"If the xenon is dirty, we won't see the signal from a collision with dark matter," Brown said. "Keeping the clean is one of the major challenges of this experiment, and my work involves developing new techniques and new technologies to keep pace with that challenge."

Brown also aids in calibrating the detector to ensure that interactions which are recorded can be properly identified. In rare cases, for example, the signal from a gamma ray may approach the expected signal of a , and proper calibration helps to rule out similar false positive signals.

In the paper "First Dark Matter Search Results from the XENON1T Experiment" posted on arXiv.org and submitted for publication, the collaboration presented results of a 34-day run of XENON1T from November 2016 to January 2017. While the results did not detect dark matter particles—known as "weakly interacting massive particles" or "WIMPs" - the combination of record low radioactivity levels with the size of the detector implies an excellent discovery potential in the years to come.

"A new phase in the race to detect dark matter with ultralow background massive detectors on Earth has just began with XENON1T," said Elena Aprile, a professor at Columbia University and project spokesperson. "We are proud to be at the forefront of the race with this amazing detector, the first of its kind."

Explore further: XENON1T, the most sensitive detector on Earth searching for WIMP dark matter, releases its first result

More information: "First Dark Matter Search Results from the XENON1T Experiment," arxiv.org/abs/1705.06655

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Aug 22, 2017
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1.6 / 5 (7) Aug 22, 2017
I blame over-funding for (non)science for contributing to the generally confusing air surrounding DM, DE and other assorted strange theories (remember Higgs Boson -"conferring mass on particles"? nonsense) and this is just an example of more dipping into the box of underused terms, for effect, to support mostly speculative but undeniably imaginative theorizing. We've all seen the images of the "creation of electron-positron pairs" in a bubble chamber - they must be opposites because they are veering into opposite dimensions - therefore 'positrons'! Did you know that when you pass a stream of silver atoms through a magnetic field, half of them veer off into one direction and the other half veer off into the other direction? And yet they are still silver atoms. Those electron-positron pairs are two electrons with opposite spins, but they are still electrons. Electrons occur in pairs. DM is bad math.
Aug 23, 2017
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1 / 5 (3) Aug 23, 2017
If you can't see dark matter/energy what did they make their detector out of to detect what? DM and DE are figments of someone's imagination. Don't understand something you're seeing in space, then let's create some stuff to explain it. NOT!
4.4 / 5 (7) Aug 23, 2017
I dunno what XENON is searching for, because the XENON1T is fourth generation of WIMP detectors already. Once we cannot find particles with detector which is one thousand-times more sensitive than the original one projected according to theory, then the theory has been excluded with reliability 1000:1 already.

Because we all know that increasing the sensitivity of LIGO over the years led to no results, right?
Aug 23, 2017
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Aug 23, 2017
This comment has been removed by a moderator.
4.2 / 5 (5) Aug 23, 2017
Errr, have I accidentally stumbled into some kinda trollmoot?
5 / 5 (1) Aug 25, 2017
I wonder how sensitive they will need to make these machines before they realize what they are looking for doesn't exist. It makes me want to get a PhD in astrophysics just so I can point everyone in the right direction.
5 / 5 (1) Aug 25, 2017
@Merrit: If you got a PhD in astrophysics, you would be obligated to follow the mainstream paradigm, and your research would take you into directions determined by the funding committee, and you'd be thinking, "I've got a wife and kids..," and the the rest would play itself out predictably.

For my part, I'd rather be a crank.
not rated yet Aug 25, 2017
@baudrunner that is not necessarily true. I already have a suspicion where the issue is located and could help investigate.

1. I believe we do not understand nor apply time dilation from relativity 100% correctly. Very complicated to go into details of what may be off, bit there are several experiments I could do.

2. The expansion of the universe is taken for a given when it is far from certain. There are a few experiments I could do to actually verify if the universe is expanding.
Aug 26, 2017
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3 / 5 (2) Aug 31, 2017
"Hey let me tell you why these things are not gonna work based on my intense internet research on obscure websites about entangled quantum vibrations in the brain!"
"The electric-omegon-orgasmatron theory i made up years ago that explains all these results!"
I don't know why i bother reading the comments.

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