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Old 25-01-2019, 10:48 AM
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COSINE-100 experiment fails to detect WIMP dark matter candidate in first 59.9 days

In a press release by the São Paulo Research Foundation (FAPSEP)
published at phys.org, it has been reported that the COSINE-100
experiment, built 700 meters underground in South Korea, has failed
to confirm the data from the DAMA/LIBRA experiment in its first 59.9 days
of operation.

The DAMA/LIBRA experiment was conducted in Italy 20 years ago and
published data at the time showed it had detected "a signal modulation
produced by an interaction with the Milky Way's dark matter halo".

Originally Posted by FAPSEP

Dark matter is believed to constitute approximately 27 percent of the known universe, with ordinary matter accounting for only 4 percent. The remaining 69 percent is thought to be made up of dark energy. Because dark matter interacts weakly with normal matter, its presence has thus far been inferred only from gravitational effects on visible bodies such as stars, galaxies and galaxy clusters.

According to the most widely accepted model, the combined motion of the Earth, the sun and the galaxy itself result in a dark matter wind for an observer on the Earth—more specifically, a wind of weakly interacting massive particles or WIMPs, hypothetical particles that are thought to constitute dark matter.

During the Earth's annual orbit around the sun, signals from the detector's interaction with WIMPs increase when the planet moves in the opposite direction to the wind and decrease when they are both moving in the same direction. The fluctuation has a cosine shape.

DAMA/LIBRA personnel state that it has detected signals at rates that vary according to a cosine wave during the year and that they correspond to a dark matter signature. The problem is that no such signature has been confirmed by any other experiments since this was first announced. It should be stressed that other experiments use different materials and analytical techniques.

To check the discrepancy between DAMA/LIBRA's data and the data from other experiments and to look for robust evidence of dark matter, COSINE-100 was built 700 meters underground at the Yangyang Underground Laboratory—Y2L in South Korea.

An article presenting the results of the first 59.5 days of data from COSINE-100 was published in December 2018 in the journal Nature.

Nelson Carlin Filho, Professor at the University of São Paulo's Physics Institute (IF-USP) and two supervisees constitute the Brazilian participation in the COSINE-100 international collaboration. "The results of the first 59.5 days of COSINE-100 failed to confirm the data from DAMA/LIBRA. The results obtained don't correspond to a signature of WIMPs," he said. Carlin stressed that this negative finding is particularly important because both DAMA/LIBRA and COSINE-100 use detectors made of sodium iodide (Nal) crystals. "It's the first published finding for a detector comprising this material with sufficient size and sensitivity to investigate the DAMA/LIBRA signal region," he said.

"We're not saying the researchers at DAMA/LIBRA were wrong. They may have captured a periodic modulation in actual signals. However, unless the dark matter model is significantly modified, the signals are highly unlikely to be attributed to interactions with WIMPs. In any event, our work is only just beginning. Several years of data will be needed before the annual modulation claimed by DAMA/LIBRA can be totally confirmed or refuted."

The COSINE-100 detector is made up of eight thallium-doped sodium iodide crystals with a total mass of 106 kg. Each crystal is coupled to two photomultiplier tubes to measure the amount of energy deposited in the crystal. The entire array is immersed in 2,200 liters of liquid scintillator and surrounded by copper, lead and plastic scintillator panels.

Press Release here :- https://phys.org/news/2019-01-detect...ence-dark.html
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