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The Large Underground Xenon Detector (LUX) recently released results1 that they have found no signs of dark matter2 after a ~3 month search this spring and summer. The LUX group plans to spend all of 2014 looking for dark matter interactions with the liquid xenon. (I thought I read somewhere that they were planning on doubling the amount of xenon, but cannot find a link that confirms this).

Early last year, researchers from Chile reported that there was no significant amount of dark matter in the solar vicinity3. They studied4 the motions of about 400 stars within 13,000 lightyears radius from the sun, and all the matter is accounted for in what we see: gas, dust, star, etc., and there's little room for dark matter.

Does it make sense to continue searching for dark matter via direct detection method when research suggests there's nothing to find in our solar vicinity?

Would it make more sense to build more sensitive space-based detectors?


1 preprint, Akerib et al 2013

2 article, K Jepsen, Symmetry Magazine, 2013

3 article, ESO, Phys.Org, 2012

4 preprint, Mono Bidin et al 2012

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    $\begingroup$ Most of the direct dark matter experiments have been and are still are ramping up sensitivity. These experiments represent a new horizon in low-background instrumentation and are delicate, difficult and expensive to build and operate. The funding agencies dribble out the money for that kind of thing in stages to allow the experiments to show that they can reach their stated goals before they get all the money. $\endgroup$ – dmckee Oct 31 '13 at 23:46
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    $\begingroup$ What is happening now is that some of the machines are starting to get into new sensitivity territory and to be able to start winnowing out some models and some parts of the allowed phase space. So they publish an early paper or two while that still have considerable improvement ahead of them. Until two or three of the machines get close to their design goals with negative results no one is going to be pushing for changes in the current program. $\endgroup$ – dmckee Oct 31 '13 at 23:55
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    $\begingroup$ The analysis by Mono Bidin was completely wrong, which was demonstrated by Scott Tremaine, one of the world experts on galactic dynamics (he literally wrote the text book on the subject). His analysis of the same data was in fact in complete agreement with the expected amount of dark matter. Bottom line: never believe over-hyped press releases. $\endgroup$ – Pulsar Nov 1 '13 at 0:35
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    $\begingroup$ @julianfernandez: please note Pulsar's comment about the Mono Bidin analysis being wrong. The first question, therefore, is based on an faulty premise. However, the second question is still a valid question to ask. $\endgroup$ – Kyle Kanos Aug 27 '14 at 14:42
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    $\begingroup$ If there's no dark matter within 13,000 light-years of Earth, then why would space-based detectors be any better than Earth-based ones? We can't send detectors out that far. $\endgroup$ – tparker Jul 7 '17 at 18:47
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In short, yes it completely makes sense to keep searching for Dark Matter using Earth-based direct-detection equipment.

Even in the case that there is no significant amount of dark matter in the Solar vicinity, that is the only area we are currently able to search using direct-detection. So it makes sense that if we search for dark matter (and we should search for dark matter because finding would be immensely good for mostly all of physics) we should search for it in the only place we are able to.

But that doesn't mean we shouldn't switch to space-based searching right? Yes and no. No doubt, a space-based detector would have a greater range of testing locations and less ground-based interference sources. But that's about all the benefits. Remember that we expect dark matter to be very weakly interacting if it interacts at all. This is why the Earth-based detectors are deep underground and/or heavily shielded (much like neutrino detectors when you think about it). In space, the amount of shielding a detector can have is limited because shielding is heavy and heavy is expensive. Plus there is a lot more radiation and sources of interference in space than on Earth. Plus, typically, space-based sensors never begin to rival the sensitivity of Earth-based ones (that is, the technology doesn't rival it, the sensitivity could be better if space produces less noise in the data, but it won't in this case). Also, and again, it's bloody expensive to send stuff into space and retrieve the data. For the price of a low sensitivity space-craft, we could build a much better detector on Earth. And the amount of dark matter within the areas in space that we could position such a detector is probably about the same as the amount here on Earth.

But, and this is strictly for the record, let's assume that there's some small isolated pocket of dark matter that we expect to find in Earth's L2 point around the Sun. Should we build space-craft and equip detectors and send them there? YES! Should we stop building or even using detectors on Earth? No. Why would we? What if we get no detection from that pocket? Or what if we don't want to constantly send out expensive new equipment? We can do both, build space detectors and use Earth detectors. So even if space-based detectors might give us a higher chance of detection, it would still make sense to keep using Earth-based detectors.

So in short, yes it is completely sane; it makes sense to continue searching for dark matter on Earth. We can't position a direct-detector very far from Earth. We need a direct-detection eventually, so we should keep looking. And space-based sensors are more expensive, less shielded, harder to maintain, and have more sources for false positives than Earth-based sensors.

The science may say that we shouldn't expect to or it isn't very likely that we will find dark matter around here. But until we have any better options (and given that we have to search), it still makes sense for us to search on Earth.

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It would be remarkable if there were no dark matter in the vicinity of the Earth. As far as we know, the hypothesised properties of dark matter mean that it should be quite smoothly distributed. If we can't find any here on Earth, why should we find it anywhere else? Therefore it makes perfect sense to push sensitivity limits as low as possible here on Earth.

Moni Bidin et al. are sticking to their guns on there being no (negligible) dark matter in the solar vicinity, but the measurements and interpretation are difficult and plenty disagree (e.g. Bovy & Tremaine 2012; Garbari et al. 2011). So from that point of view, the controversial thesis in your question should not be sufficient to shut down an entire research area without a lot more hard evidence that achieves a consensus.

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