The AstroStat Slog » DAMA http://hea-www.harvard.edu/AstroStat/slog Weaving together Astronomy+Statistics+Computer Science+Engineering+Intrumentation, far beyond the growing borders Fri, 09 Sep 2011 17:05:33 +0000 en-US hourly 1 http://wordpress.org/?v=3.4 Is 8-sigma significant enough for you? http://hea-www.harvard.edu/AstroStat/slog/2008/dark-matter-modulation/ http://hea-www.harvard.edu/AstroStat/slog/2008/dark-matter-modulation/#comments Thu, 24 Apr 2008 18:56:58 +0000 vlk http://hea-www.harvard.edu/AstroStat/slog/?p=279 There is a new report from Bernabei et al. (arXiv:0804.2741) of the direct detection of the effects of Dark Matter that is causing a lot of buzz. (The Bad Astronomer has a good summary.) They find yearly modulation in their detected scintillation rate that matches what you would expect if the Earth were rushing through Galactic Dark Matter as it goes around the Sun. They have worked out the significance of the modulation to be 8.2 sigma. Significant! But significant of what?

I am no expert on this in a hundred and one different ways. But I feel kinda sorry for the DAMA group. Certainly, at 8-sigma, it is easy to accept that there is modulation. But is this modulation proof of Dark Matter? Astronomers in general are extremely suspicious of any yearly modulations, as we have learnt from hard experience that it is an extremely common source of systematic error. Essentially, the Earth is a poorly calibrated detector, and it has diurnal and annual cycles, and these invariably show up in everything. So when the signal you are looking for goes exactly like the first thing you try to catch and eliminate, what price statistical significance?

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