The LUX dark matter search experiment announced its first results this morning, almost totally ruling out previous experiments that had evidence for dark matter particles at low mass. LUX had expected 1550 dark matter events if the other detections were valid, but could not claim any events that were not consistent with background. They also set new limits on higher mass dark matter, which is 20 times better than previous limits.
Now for some background. LUX is at the Sanford Underground Research Facility in the old Homestake mine in South Dakota. That is where Ray Davis detected only a third of expected solar neutrinos that led to the theories of neutrino oscillations and neutrino conversions in the sun. T. Denney Sanford donated $70 million to the lab, and the State of South Dakota $30 million.
Dark matter is about 25% of the energy of the universe, our ordinary matter is about 5%, and dark energy is the other 70%. Dark matter is dark because it is neutral, and only interacts gravitationally, and possibly through the weak interactions.
The LUX experiment has 118 kilograms (260 pounds) of Xenon as target (called fiducial volume), deep underground. Their sites are at sanfordlab.org and luxdarkmatter.org . The latter has the talks this morning by Daniel McKinsey of Yale University, and Richard Gaitskell of Brown University.
The new limits are from 85 days of running. More results will be reported after an additional 300 days in 2014/2015, when the results will increase the sensitivity by a factor of 5.
The low mass dark matter ruled out were 6-10 GeV masses of Weakly Interacting Massive Particles (WIMPS).
The next dark matter experiment there will be a collaboration of LUX – Zeppelin, which will produce results 1000 times more sensitive than today’s. That will be after three years of running, and could be running at the latter part of this decade.