Astrophysical evidence suggests that the universe contains a large amount of non-luminous dark matter, yet no definite signal of it has been observed despite concerted efforts by many experimental groups. One exception to this is the long-debated claim by the DArk MAtter (DAMA) collaboration, which has reported positive observations of dark matter in its sodium-iodide detector array.
The new COSINE-100 experiment, based at an underground, dark-matter detector at the Yangyang Underground Laboratory in South Korea, has begun to explore DAMA’s claim. It is the first experiment sensitive enough to test DAMA and use the same target material of sodium iodide.
COSINE-100 has been recording data since 2016 and now has initial results that challenge the DAMA findings. Those findings are published online this week in the journal Nature.
And what happened?
“The initial results carve out a fair portion of the possible dark matter search region drawn by the DAMA signal. In other words, there is little room left for this claim to be from the dark matter interaction unless the dark matter model is significantly modified,” said Hyun Su Lee, the other co-spokesperson for COSINE-100, and an associate director of the Center for Underground Physics at IBS. Paper. (paywall) – From Yale University, based on he COSINE-100 Collaboration. An experiment to search for dark-matter interactions using sodium iodide detectors. Nature, 2018 DOI: 10.1038/s41586-018-0739-1 More.
The researchers are 90% confident they have ruled dark matter out:
The COSINE-100 team will now work on determining whether its detectors observe a seasonal cycle of nonbackground detections. Due to the sensitivity of the crystals and an unexpected shortfall in detector performance, that probably requires about three more years of data collection. But other NaI-based experiments are on the case, and COSINE-100 may share data with one of them, ANAIS in the Spanish Pyrenees, to speed up the process. With further progress on the NaI front, researchers may finally be able to peg DAMA’s signal to instrument error, an overlooked atmospheric or cosmic interloper, or a more exotic variety of dark-matter particle. (COSINE-100 collaboration, Nature 564, 83, 2018.) Andrew Grant, “Long-standing dark-matter detection claim takes a hit” at Physics Today
Frustrating but better to know.
See also: Discover: Even the best dark matter theories are crumbling
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