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Most experiments that try to directly detect dark matter have looked for WIMPs (weakly interacting massive particles). However, as those searches have not borne fruit, the focus started turning to axions, which make for good candidates given their properties and the fact that if they exist, then they exist in multitudes throughout the galaxies. Axions \u201cspeak\u201d to the QCD part of the Standard Model, so they can appear in interaction vertices with hadronic loops. The end result is that axions passing through a magnetic field will convert to photons.<\/p>\n\n\n\n
In practical terms, their detection boils down to having strong magnets, sensitive electronics and an electromagnetically very quiet place at one\u2019s disposal. One can then sit back and wait for the hypothesized axions to pass through the detector as earth moves through the dark matter halo surrounding the Milky Way. Which is precisely why such experiments are known as \u201chaloscopes.\u201d<\/p>\n\n\n\n
Now, the most veteran haloscope of all published significant new results. Alas, it is still empty-handed, but we can look at why its update is important and how it was reached.<\/p>\n\n\n\n
ADMX (Axion Dark Matter eXperiment) of the University of Washington has been around for a quarter-century. By listening for signals from axions, it progressively gnaws away at the space of allowed values for their mass and coupling to photons, focusing on an area of interest:<\/p>\n\n\n\n
![\"ADMX_results_2020\"](\"https:\/\/www.particlebites.com\/wp-content\/uploads\/2020\/05\/admx4.png\")
<\/a>Unlike higher values, this area is not excluded by astrophysical considerations (e.g. stars cooling off through axion emission) and other types of experiments (such as looking for axions from the sun). In addition, the bands above the lines denoted \u201cKSVZ\u201d and \u201cDFSZ\u201d are special. They correspond to the predictions of two models with favorable theoretical properties. So, ADMX is dedicated to scanning this parameter space. And the new analysis added one more year of data-taking, making a significant dent in this ballpark.<\/p>\n\n\n\n
As mentioned, the presence of axions would be inferred from a stream of photons in the detector. The excluded mass range was scanned by \u201ctuning\u201d the experiment to different frequencies, while at each frequency step longer observation times probed smaller values for the axion-photon coupling.<\/p>\n\n\n\n
Two things that this search needs is a lot of quiet and some good amplification, as the signal from a typical axion is expected to be as weak as the signal from a mobile phone left on the surface of Mars (around 10-23<\/sup>W). The setup is indeed stripped of noise by being placed in a dilution refrigerator, which keeps its temperature at a few tenths of a degree above absolute zero. This is practically the domain governed by quantum noise, so advantage can be taken of the finesse of quantum technology: for the first time ADMX used SQUIDs, superconducting quantum interference devices, for the amplification of the signal.<\/p>\n\n\n\n In the end, a good chunk of the parameter space which is favored by the theory might have been excluded, but the haloscope is ready to look at the rest of it. Just think of how, one day, a pulse inside a small device in a university lab might be a messenger of the mysteries unfolding across the cosmos.<\/p>\n\n\n\n References: <\/strong><\/p>\n\n\n\n Publication<\/a> by the ADMX collaboration. (arXiv<\/a>)<\/p>\n\n\n\n Learn more: <\/strong><\/p>\n\n\n\n Updates from the most veteran axion hunting experiment. <\/p>\n","protected":false},"author":31,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[47,38,57],"tags":[80,79,10],"class_list":["post-7176","post","type-post","status-publish","format-standard","hentry","category-beyond-standard-model","category-dark-matter","category-experimental-techniques","tag-axions","tag-bsm","tag-dark-matter"],"_links":{"self":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts\/7176","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/users\/31"}],"replies":[{"embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=7176"}],"version-history":[{"count":25,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts\/7176\/revisions"}],"predecessor-version":[{"id":7301,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=\/wp\/v2\/posts\/7176\/revisions\/7301"}],"wp:attachment":[{"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7176"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7176"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.particlebites.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7176"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/www.particlebites.com\/wp-content\/uploads\/2020\/05\/Cutaway-view-of-the-ADMX-cryostat_W640.jpg\")
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