Physics & Astronomy Colloquium

3:30 PM, Friday, September 21, 2007
Room 155, Chem-Phys Building

Dr. Rick Gaitskell
Department of Physics
Brown University

" Noble Travails: XENON10, LUX and Other Noble Liquid Detectors Searching for Particle Dark Matter ''

Particle dark matter is thought to be the overwhelming majority of the matter in the Universe, dwarfing the contribution from conventional material that we, the earth and the stars, are composed of. However, we still have no direct evidence for the existence of?Particle dark matter. This may soon change...

I will report on the latest results from the XENON10 liquid xenon-based detector which began searching for particle dark matter at Gran Sasso in late 2006 (http://xenon.brown.edu). The experiment has already demonstrated (http://arxiv.org/abs/0706.0039) a world class direct search sensitivity which is a factor 4 better than its current nearest rival (CDMS II). I will discuss some of the details of the experiment, and future evolution.

I will also discuss some of the other noble liquid target experiments that are also providing competitive sensitivities in the race for the direct detection of particle dark matter (WIMPs). Theoretical estimates, based on supersymmetric models predict dark matter interaction rates from the best sensitivity of existing direct detection experiments of ~1 evts/kg/month, down to rates of ~1 evts/100 kg/yr, and below this. Current noble liquid experiments for dark matter searches, range in scale from 10 to 100's kg, and are designed to rise to this challenge.

Ar, Ne and Xe targets permit the discrimination of electron recoils, coming from gamma ray and beta backgrounds, versus nuclear recoils, characteristic of WIMP events. This is done using scintillation light pulse shapes, and/or the ratio of ionization to scintillation generated in the target by the interaction. Latest results show this discrimination is extremely effective, even at low energies. The detectors are also able to significantly reduce backgrounds through the use of position resolution in large volumes, combined with active self-shielding, to reach very low levels in inner fiducial volumes.

A growing understanding of how to exploit these characteristics, and construct larger detectors, will allow further significant improvements in the sensitivity of noble liquid experiments. My discussion will include current and future noble liquid detector experiments: LUX, miniCLEAN/DEAP, WARP, XENON, XMASS, ZEPLIN.

Refreshments will be served in CP 179 at 3:15 PM