Scientists piece together the largest U.S.-based dark matter experiment

Some assembly required: scientists piece together the largest U.S.-based dark matter experiment
Upper (left) and lower photomultiplier tube arrays are prepared for LZ at the Sanford Underground Research Facility in Lead, South Dakota. Credit: Matt Kapust/SURF

Most of the remaining components needed to fully assemble an underground dark matter-search experiment called LUX-ZEPLIN (LZ) arrived at the project's South Dakota home during a rush of deliveries in June.

When complete, LZ will be the largest, most sensitive U.S.-based experiment yet that is designed to directly detect dark matter particles. Scientists around the world have been trying for decades to solve the mystery of dark matter, which makes up about 85 percent of all matter in the universe though we have so far only detected it indirectly through observed gravitational effects.

The bulk of the digital components for LZ's electronics system, which is designed to transmit and record signals from ever-slight particle interactions in LZ's core detector vessel, were among the new arrivals at the Sanford Underground Research Facility (SURF). SURF, the site of a former gold mine now dedicated to a broad spectrum of scientific research, was also home to a predecessor search experiment called LUX.

A final set of snugly fitting acrylic vessels, which will be filled with a special liquid designed to identify false dark matter signals in LZ's inner detector, also arrived at SURF in June.

Also, the last two of four intricately woven wire grids that are essential to maintain a constant electric field and extract signals from the experiment's inner detector, also called the time projection chamber, arrived in June (see related article).

Some assembly required: scientists piece together the largest U.S.-based dark matter experiment
An intricately thin wire grid is visible (click image to view larger size) atop an array of photomultiplier tube. The components are part of the LZ inner detector. Credit: Matt Kapust/SURF

"LZ achieved major milestones in June. It was the busiest single month for delivering things to SURF—it was the peak," said LZ Project Director Murdock Gilchriese of the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab). Berkeley Lab is the lead institution for the LZ project, which is supported by an international collaboration that has about 37 participating institutions and about 250 researchers and technical support crew members.

"A few months from now all of the action on LZ is going to be at SURF—we are already getting close to having everything there," Gilchriese said.

Mike Headley, executive director at SURF, said, "We've been collectively preparing for these deliveries for some time and everything has gone very well. It's been exciting to see the experiment assembly work progress and we look forward to lowering the assembled detector a mile underground for installation."

All of these components will be transported down a shaft and installed in a nearly mile-deep research cavern. The rock above provides a natural shield against much of the constant bombardment of particles raining down on the planet's surface that produce unwanted "noise."

LZ components have also been painstakingly tested and selected to ensure that the materials they are made of do not themselves interfere with particle signals that researchers are trying to tease out.

Some assembly required: scientists piece together the largest U.S.-based dark matter experiment
Components for the LUX-ZEPLIN project are stored inside a water tank nearly a mile below ground. The inner detector will be installed on the central mount pictured here, and acrylic vessels (wrapped in white) will fit snugly around this inner detector. Credit: Matt Kapust/SURF

LZ is particularly focused on finding a type of theoretical particle called a weakly interacting massive particle or WIMP by triggering a unique sequence of light and electrical signals in a tank filled with 10 metric tons of highly purified liquid xenon, which is among Earth's rarest elements. The properties of xenon atoms allow them to produce light in certain particle interactions.

Proof of would fundamentally change our understanding of the makeup of the universe, as our current Standard Model of Physics does not account for their existence.

Assembly of the liquid xenon time projection chamber for LZ is now about 80 percent complete, Gilchriese said. When fully assembled later this month this inner detector will contain about 500 photomultiplier tubes. The tubes are designed to amplify and transmit signals produced within the chamber.

Once assembled, the time projection chamber will be lowered carefully into a custom titanium vessel already at SURF. Before it is filled with xenon, this chamber will be lowered to a depth of about 4,850 feet. It will be carried in a frame that is specially designed to minimize vibrations, and then floated into the experimental cavern across a temporarily assembled metal runway on air-pumped pucks known as air skates.

Finally, it will be lowered into a larger outer titanium vessel, already underground, to form the final vacuum-insulated cryostat needed to house the liquid xenon.

Some assembly required: scientists piece together the largest U.S.-based dark matter experiment
An array of photomultiplier tubes that are designed to detect signals occurring within LZ’s liquid xenon tank. Credit: Matt Kapust/SURF

That daylong journey, planned in September, will be a nail-biting experience for the entire project team, noted Berkeley Lab's Simon Fiorucci, LZ deputy project manager.

"It will certainly be the most stressful—this is the thing that really cannot fail. Once we're done with this, a lot of our risk disappears and a lot of our planning becomes easier," he said, adding, "This will be the biggest milestone that's left besides having in the detector."

Project crews will soon begin testing the xenon circulation system, already installed underground, that will continually circulate xenon through the inner detector, further purify it, and reliquify it. Fiorucci said researchers will use about 250 pounds of xenon for these early tests.

Work is also nearing completion on LZ's cryogenic cooling system that is required to convert xenon gas to its liquid form.

LZ digital electronics, which will ultimately connect to the arrays of photomultiplier tubes and enable the readout of signals from particle interactions, were designed, developed, delivered, and installed by University of Rochester researchers and technical staff at SURF in June.

Some assembly required: scientists piece together the largest U.S.-based dark matter experiment
Researchers from the University of Rochester in June installed six racks of electronics hardware that will be used to process signals from the LZ experiment. Credit: University of Rochester

"All of our electronics have been designed specifically for LZ with the goal of maximizing our sensitivity for the smallest possible signals," said Frank Wolfs, a professor of physics and astronomy at the University of Rochester who is overseeing the university's efforts.

He noted that more than 28 miles of coaxial cable will connect the photomultiplier tubes and their amplifying electronics—which are undergoing tests at UC Davis—to the digitizing electronics. "The successful installation of the and the online network and computing infrastructure in June makes us eager to see the first signals emerge from LZ," Wolfs added.

Also in June, LZ participants exercised high-speed data connections from the site of the experiment to the surface level at SURF and then to Berkeley Lab. Data captured by the detectors' electronics will ultimately be transferred to LZ's primary data center, the National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab via the Energy Sciences Network (ESnet), a high-speed nationwide data network based at Berkeley Lab.

The production of the custom acrylic tanks (see related article), which will contain a fluid known as a liquid scintillator, was overseen by LZ participants at University of California,Santa Barbara.

"The last five tanks, delivered in June, were fabricated using a novel acrylic molding process to closely fit around the cryostat vessel," said Harry Nelson, professor of physics at UC Santa Barbara.

"The partnership between LZ and SURF is tremendous, as evidenced by the success of the assembly work to date," Headley said. "We're proud to be a part of the LZ team and host this world-leading experiment in South Dakota."

Some assembly required: scientists piece together the largest U.S.-based dark matter experiment
The bottom three acrylic tanks for the LUX-ZEPLIN outer detector during testing at the fabrication vendor. These tanks are now at the Sanford Underground Research Facility in Lead, South Dakota. Credit: LZ Collaboration

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Jul 17, 2019
I just have a dumb question. But if 85% of the mass around us is dark matter, why do the current models fit so perfectly to the gravity we see in the Solar System? It should be screwed up if there was invisible dark matter, too. If there is no dark matter in the Solar System, then how can an experiment such as this one detect any?

Jul 17, 2019
If dark matter is evenly spread below a certain space scale then you cannot "see" it below that scale, which is why it (presumably) is not evident in the Solar System. It's like gravitationally detecting water inside an ocean.

Jul 17, 2019
always fun.

Jul 17, 2019
If dark matter is evenly spread below a certain space scale then you cannot "see" it below that scale, which is why it (presumably) is not evident in the Solar System. It's like gravitationally detecting water inside an ocean.

A quite good hypothesis.
Wish them luck.

Jul 17, 2019
Gigel, your explanation doesn't make any sense to me. How can DM be spread evenly in the Solar System when there is the sun and planets? It should be affected just like any other matter by gravity. And if it is present and not spread evenly, then the current models wouldn't work.

Jul 17, 2019
Please see Possible Dark Matter Mass Candidates in Spinning Sphere Theory by Michael John Sarnowski

Jul 17, 2019
In search of black holes and dark matter astrophysicists are relying on indirect observations. It would seem that the measurement of the event horizon of a black hole directly would be a direct evidence. However, by the nature of a horizon, any real measurement of the event horizon will be indirect. The Event Horizon Telescope will get picture of the silhouette of the Sgr A* which is due to optical effects of spacetime outside of the event horizon. The result will be determined by the simple quality of the resulting image that does not depend on the properties of the spacetime within the image. So, it will be also indirect and an existence of BH is a hypothesis.
https://www.acade...ilky_Way
https://www.acade...k_Energy

Jul 17, 2019
So they have commissioned Led Zeppelin to detect and find the unobservable and undetectable Dark Matter in order to placate and satisfy the whims of the Dark Matter cultists. And all of that expensive and expansive equipment that Led Zeppelin will undoubtedly use for the purpose of determining whether or not the Dark Matter faerie dust has fallen into their trap. This Woo Bubble in which Led Zeppelin is to take part in will not be very profitable, as woo never is. The rare Highly Purified Liquid Xenon - I wonder how much they paid for THAT?
But good luck to them even if it takes forever. While they're at it - play some good music.

Jul 17, 2019
Gigel, your explanation doesn't make any sense to me. How can DM be spread evenly in the Solar System when there is the sun and planets? It should be affected just like any other matter by gravity. And if it is present and not spread evenly, then the current models wouldn't work.
says Bart_A

The human eye is very good at detecting Dark Matter. Each night when a human closes his eyes and falls asleep, the Dark Matter slowly creeps into his field of vision and everything turns black. It is Dark Matter that is the backdrop for dreams, similar to a dark curtain in a movie theatre.
That 85% that is said to be Dark Matter is actually all around us when the lights are turned off at night. If not by the light of the Moon and Stars, the Dark Matter would completely envelope the Earth and most of the Solar System (except where the Sun shines).
I'm not kidding, Bart. All that Dark Matter is, is the absence of light. Light from Stars, planets, moons, hot gases chases away DM.

Jul 17, 2019
The human eye is very good at detecting Dark Matter. Each night when a human closes his eyes and falls asleep, the Dark Matter slowly creeps into his field of vision and everything turns black. It is Dark Matter that is the backdrop for dreams, similar to a dark curtain in a movie theatre.
That 85% that is said to be Dark Matter is actually all around us when the lights are turned off at night. If not by the light of the Moon and Stars, the Dark Matter would completely envelope the Earth and most of the Solar System (except where the Sun shines)I'm not kidding, Bart. All that Dark Matter is, is the absence of light. Light from Stars, planets, moons, hot gases chases away DM..
.......I see there's becoming less need for Benni carrying this DM baton, Egg is picking it up running faster with it than I have in the past, I've needed a vacation from here for a long time, maybe it's time?

Jul 17, 2019
No. There is no place to go where you can escape the physorg Dark Matter cultists, Benni. They are everywhere (almost). They will find you and hound you until you agree with them. But if you tell them to close their eyes in a darkened room, they will find the Dark Matter which they seek, and they will thank you.

Jul 18, 2019
@Benni
The long sought Dark Matter flees Light - any kind of Light, such as SunLight, MoonLight, StarLight, CandleLight, FlashLight, Lightning, FireLight, even Fireflies on a hot summer's eve.
Most human scientists and cultists have expected that Dark Matter to be so exotic and mysterious, as well as indefinable, when all it is, is Darkness, which is the complete lack of Photons. Dark Matter is also comprised of Quantum Particles which is the part of it that is Matter. The back of caves, especially those that are underground, are notorious for harbouring Dark Matter.
But Dark Matter is elusive.

Jul 18, 2019
When you reach a certain level of power the ability to annoy people becomes an indispensable tool for further advancement. Dark matter is priceless, an imaginary gift that never stops giving to the chosen elite, it saved general relativity, when true gravity, beautiful and pure, was extremely young and vulnerable to hatred, from falsification forever, it is a promise written in the sky, as if by someone who does not play dice, for all time.

Jul 18, 2019
Dark matter is like being surrounded by an ocean, and someone is pushing your head below the surface if you don't like it. This makes dark matter the most fun you can have as a physicist.

Jul 18, 2019
Bart A, dark matter would be quite homogeneous if composed of some warm particles. If composed of cold particles, then it may be concentrated inside the Sun or planets. But we detect particles here on Earth, so that would not be of much help.

On the other hand, there were several experiments showing some weird annual variation in nuclear radioactivity and some axion detectors...

Jul 18, 2019
Gigel, your explanation doesn't make any sense to me. How can DM be spread evenly in the Solar System when there is the sun and planets? It should be affected just like any other matter by gravity. And if it is present and not spread evenly, then the current models wouldn't work.
Let's take the simplest case: suppose DM is a discrete-particle/thingamajig phenomenon, and suppose these thingamies were evenly distributed throughout the galaxy. And then, because this is a conceptual simplification, suppose the   d e n s i t y   of DM that is sufficient for the galaxy-wide Keplerian anomaly would mean only one DM whatsit per cubic parsec. Would we see a local (solar system) deviation from Keplerian orbital dynamics?

Now, this would approximate the tiny-Black-Hole hypothesis for DM (sort of), but the argument would hold for a greater density of smaller particles. But I'm running out of fizz·org comment-field space.

Aug 12, 2019
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