All Quiet on the Dark Front

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Science  29 Oct 2010:
Vol. 330, Issue 6004, pp. 563
DOI: 10.1126/science.330.6004.563-a

Astrophysical observations suggest that the mass content of the universe is dominated by dark matter that neither emits nor absorbs radiation and is thus invisible. Its as yet unobserved constituents, probably neutral Big Bang relics called weakly interactive massive particles (WIMPs for short), should be detectable on Earth because they are expected to scatter off atomic nuclei, but the prospects are daunting: Detection rates could range from one event per kilogram of matter per year to less than one event per ton of matter per year. It is thus not surprising that the analysis of the first 11.17 days of data from the Xenon100 experiment, reported by Aprile et al., does not show any evidence for dark matter interactions. Xenon100 is designed to detect WIMPs scattering off 62 kg of ultrapure liquid xenon, a material selected for its high atomic mass, and hence large nucleus, associated with higher detection probability. Like other dark matter experiments, the success of Xenon100 depends on minimizing and discriminating against background events arising from radioactivity and cosmic rays. Encouragingly, the first dark matter results from Xenon100 suggest that, by design, the experiment is essentially background-free.

Phys. Rev. Lett. 105, 131302 (2010).

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