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	<title>The AstroStat Slog &#187; year</title>
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		<title>Is 8-sigma significant enough for you?</title>
		<link>http://groundtruth.info/AstroStat/slog/2008/dark-matter-modulation/</link>
		<comments>http://groundtruth.info/AstroStat/slog/2008/dark-matter-modulation/#comments</comments>
		<pubDate>Thu, 24 Apr 2008 18:56:58 +0000</pubDate>
		<dc:creator>vlk</dc:creator>
				<category><![CDATA[News]]></category>
		<category><![CDATA[arXiv]]></category>
		<category><![CDATA[DAMA]]></category>
		<category><![CDATA[dark matter]]></category>
		<category><![CDATA[Earth]]></category>
		<category><![CDATA[modulation]]></category>
		<category><![CDATA[orbit]]></category>
		<category><![CDATA[scintillation]]></category>
		<category><![CDATA[systematic error]]></category>
		<category><![CDATA[year]]></category>

		<guid isPermaLink="false">http://groundtruth.info/AstroStat/slog/?p=279</guid>
		<description><![CDATA[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 [...]]]></description>
			<content:encoded><![CDATA[<p>There is a new report from Bernabei et al. (<a href="http://arxiv.org/abs/0804.2741">arXiv:0804.2741</a>) of the direct detection of the effects of Dark Matter that is causing a lot of buzz.  (The <a href="http://www.badastronomy.com/bablog/2008/04/21/dark-matter-detected/">Bad Astronomer</a> 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?<span id="more-279"></span></p>
<p>I am no expert on this in a hundred and one different ways.  But I feel kinda sorry for the <a href="http://people.roma2.infn.it/~dama/web/home.html">DAMA</a> 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?</p>
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