Archive for October 31, 2013

Lux et Veritas

Posted in The Universe and Stuff with tags , , , , on October 31, 2013 by telescoper

There’s an important and interesting paper just out on the arxiv by the Lux Dark Matter Collaboration. Here is the abstract:

The Large Underground Xenon (LUX) experiment, a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), was cooled and filled in February 2013. We report results of the first WIMP search dataset, taken during the period April to August 2013, presenting the analysis of 85.3 live-days of data with a fiducial volume of 118 kg. A profile-likelihood analysis technique shows our data to be consistent with the background-only hypothesis, allowing 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 7.6×10−46 cm2 at a WIMP mass of 33 GeV/c2. We find that the LUX data are in strong disagreement with low-mass WIMP signal interpretations of the results from several recent direct detection experiments.

For those of you not up with the lingo, a WIMP in this context is a Weakly Interacting Massive Particle, one of the preferred candidates for the dark matter that most cosmologists think pervades the Universe.

The most important thing about the LUX results is that they pretty much exclude results from previous experiments, especially DAMA/LIBRA, that have claimed evidence for dark matter particles at low mass (i.e. 6-10 GeV WIMPS): 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. These new limits are from 85 days of running the experiment; further results will be reported after an additional 300 days in 2014/2015, when the results will increase the sensitivity by a factor of five or so.

So the question is, if LUX is correct, what on Earth is going on at DAMA? Answers on a postcard, or through the comments box, please!


Hymn for the Day

Posted in Politics with tags , , , , , on October 31, 2013 by telescoper

This morning’s hymn is Sine Nomine, No. 641 from the English Hymnal, and is chosen in honour of those participating in today’s strike of some University staff.