Physicists contribute to dark matter detector success

February 21, 2018, University of Massachusetts Amherst
Undergraduate Arthur Kurlej welding the grid electrode onto its support ring inside the radon-suppressed clean room in the underground laboratory at Gran Sasso, Italy. Kurlej's advisor, physics professor Andrea Pocar, says undergraduates were notably helpful in designing and making this component of the dark matter detector there, known as DarkSide-50. Credit: UMass Amherst

In researchers' quest for evidence of dark matter, physicist Andrea Pocar of the University of Massachusetts Amherst and his students have played an important role in designing and building a key part of the argon-based DarkSide-50 detector located underground in Italy's Gran Sasso National Laboratory.

This week, scientists from around the world who gathered at the University of California, Los Angeles, at the Dark Matter 2018 Symposium learned of new results in the search for evidence of the elusive material in Weakly Interacting Massive Particles (WIMPs) by the DarkSide-50 . WIMPs have been candidate dark particles for decades, but none have been found to date.

Pocar says the DarkSide detector has demonstrated the great potential of liquid technology in the search for so-called "heavy WIMPs," those with mass of about 100 to 10,000 times the mass of a proton. Further, he adds, the double-phase argon technique used by the DarkSide-50 detector has unexpected power in the search for "low-mass WIMPs," with only 1-10 times the mass of a proton.

He adds, "The component we made at UMass Amherst, with very dedicated undergraduates involved from the beginning, is working very well. It's exciting this week to see the first report of our success coming out at the symposium." His graduate student Alissa Monte, who has studied surface and radon-related backgrounds using DarkSide-50, will present a poster at the UCLA meeting.

Pocar says, "There is a vibrant community of researchers around the world conducting competing experiments in this 'low mass' WIMP area. Over the past two years we collected data for a measurement we didn't expect to be able to make. At this point we are in a game we didn't think we could be in. We are reporting the high sensitivity we have achieved with the instrument, which is performing better than expected." Sensitivity refers to the instrument's ability to distinguish between dark matter and background radiation.

Dark matter, Pocar explains, represents about 25 percent of the energy content of the universe and while it has mass that can be inferred from gravitational effects, physicists have great difficulty detecting and identifying it because it hardly interacts, if at all, with "regular" matter through other forces. "Dark matter doesn't seem to want to interact much at all with the matter we know about," the physicist notes.

The DarkSide-50 detector uses 50 kg (about 110 lbs.) of liquid argon in a vat, with a small pocket of argon gas at the top, Pocar explains, as a target to detect WIMPs. The researchers hope for a WIMP to hit the nucleus of an argon atom in the tank, which then can be detected by the ionization produced by the nuclear recoil in the surrounding argon medium. Some of the ionization signal, proportional to the energy deposited inside the detector, is collected by applying an to the target, he explains.

A flash of light is also produced in the argon with ionization, Pocar says. For high-enough energy events, the light pulse is bright enough to be used to tell the difference in "signature" between a nuclear recoil like that induced by a WIMP, and electron recoils induced by background or environmental radioactivity.

Pocar's lab designed, made and installed one of the electrodes that apply the electric field. He says, "For low-mass WIMPs, the amount of energy transmitted to the nucleus of argon by a WIMP is incredibly tiny. It's like hitting a billiard ball with a slow ping-pong ball. But a key thing for us is that now with two years of data, we have an exquisite understanding of our detector and we understand all non-WIMP events very well. Once you understand your detector, you can apply all that understanding in search mode, and plan for follow-up experiments."

Cristiano Galbiati, spokesperson for the DarkSide project, said at this week's symposium, "This is the best way to start the adventure of the future experiment DarkSide-20k. The results of DarkSide-50 provide great confidence on our technological choices and on the ability to carry out a compelling discovery program for dark matter. If a detector technology will ever identify convincingly induced events, this will be it."

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not rated yet Feb 21, 2018
Not optimistic and I would be surprised if his students were. It's something that has got to be done but seriously, I suspect nobody expects it to detect DM.
1 / 5 (1) Feb 21, 2018
There is evidence of the superfluid dark matter every time a double-slit experiment is performed, as it is the medium that waves.
not rated yet Feb 23, 2018
Who are those people who are persistently looking for something that does not exist in the universe? How can one try to take from the universe and question it, and is not aware at all of the structure of the universe and its power of creation? How does such a claim that in the universe exists, as it is said, 25% of dark matter, and does not even know what is dark matter, whether there is and what everything in the universe forms and from what?
There is an easy way to understand all the riddles in the universe. And that is: It is necessary to understand and accept that the universe is a sphere of infinite radius, filled with the substance AETHER, from which the matter is formed, and which is transformed again into Aether, and this happens under the influence of gravity at the places of the black hole.
You can endlessly look for something that does not exist at all, but what you are looking for is AETHER.
not rated yet Feb 23, 2018
Not optimistic and I would be surprised if his students were. It's something that has got to be done but seriously, I suspect nobody expects it to detect DM.

You never know until you look.

In any case the sensitivity increase is something that is not only useful for DM detectors. So this work isn't a waste even if they find nothing.

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