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Almost 20 years ago, the DAMA/LIBRA experiment at Italy's Gran Sasso National Laboratory—LNGS began publishing data showing that it had detected a signal modulation produced by an interaction with the Milky Way's dark matter halo.

Dark matter is believed to constitute approximately 27 percent of the known universe, with ordinary
matteraccounting 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.

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