{"id":32,"date":"2012-02-06T18:31:31","date_gmt":"2012-02-06T18:31:31","guid":{"rendered":"http:\/\/blackhole.lngs.infn.it\/darkside\/?page_id=32"},"modified":"2012-02-06T18:31:31","modified_gmt":"2012-02-06T18:31:31","slug":"ds-50","status":"publish","type":"page","link":"https:\/\/darkside.lngs.infn.it\/?page_id=32","title":{"rendered":"DS-50"},"content":{"rendered":"

After a successful prototype (DarkSide-10<\/a>) the first physics detector in the DarkSide program is\u00a0DarkSide-50 (DS-50), currently situated in\u00a0Hall C of the Gran Sasso National Laboratory (LNGS) in Assergi, Italy. DS-50 is the\u00a0first in an eventual series of\u00a0DarkSide detectors built using low-background techniques and materials and filled with low-radioactivity underground argon<\/a> (UAr). It has\u00a0an active mass of 50 kg Ar, representing the first large-scale use of low-radioactivity argon from underground sources, in addition to having a significant\u00a0experimental reach, with a sensitivity of 2 x 10-45\u00a0<\/sup>cm2<\/sup> for a WIMP mass of 100 GeV (90% C.L.) in a 3 year run. DarkSide-50 has allowed\u00a0us to fully validate important design features of the DarkSide concept, in particular those which are expected to allow the design to achieve ultra-low residual background rates in latter detectors.<\/p>\n

\"\"<\/a>
Design of DarkSide-50 liquid argon dewar containing the two-phase TPC.<\/figcaption><\/figure>\n

The DS-50 two-phase LAr TPC<\/a>\u00a0— shown in the accompanying picture — has a design based on the success of our prototype\u00a0LAr TPC, DarkSide-10. Thirty-eight 3″ Hamamatsu low-background R11065 PMTs, 19 each on the top and the bottom, view the active UAr through fused silica windows. The windows are\u00a0coated on both sides with Indium Tin Oxide (ITO), a transparent conductor. This allows the inner window surfaces to serve as the grounded anode (top) and -60 kV cathode (bottom) of the TPC while maintaining their outer surfaces near the -1.5 kV PMT photocathode potential. A gas layer for production of the electrolumnescence signature is provided by a cylindrical rim on the fused silica anode window, which extends downward to form a “diving bell” containing the 2-cm-thick argon vapor layer (“gas pocket”) above the TPC drift volume. The cylindrical vessel containing the active region is\u00a0made of PTFE (aka. Teflon), treated to be highly reflective at visible wavelengths. The entire inner surface of the active volume is\u00a0coated with the wavelength shifter TetraPhenylButadiene (TPB) which converts\u00a0the 128 nm argon scintillation into a\u00a0wavelength range detectable by the PMTs. The drift field is produced by system consisting of the ITO cathode and anode planes, a field cage, and a grid that separates the drift and electron extraction regions.<\/p>\n

The DS-50 TPC is\u00a0deployed within a 4-meter-diameter stainless steel sphere containing a borated liquid scintillato: this is our “neutron veto”, or “liquid scintillator veto” (LSV). The LSF is itself\u00a0inside the Borexino CTF (Counting Test Facility) tank<\/a>, which is filled with water and used as a\u00a0\u010cerenkov muon veto. This “nesting doll” veto arrangement not only gives\u00a0DarkSide-50 the benefits of active background suppression, but will also give us direct experience in operating a low background experiment in these active shields, to prepare for the eventual multi-ton DS-20k\u00a0experiment.<\/p>\n

DarkSide-50 construction was completed in late 2012, with physics data collection beginning in late 2013, using atmospheric argon (AAr). Although DS-50 was designed to achieve a light yield of 6 PE\/keV (at null field) with AAr, it exceeded expectations and reached nearly 8 PE\/keV. DS-50 also successfully demonstrated\u00a0that a neutron veto rejection efficiency for internally-generated neutrons could be kept above 99.5%.
\nAfter an initial analysis of about 50 days of acquired AAr data, the DarkSide Collaboration published direct dark matter WIMP search results free from all sources of remaining background (less than 0.1 events after all cuts). This gives an estimated sensitivity for spin-independent WIMP-nucleon scattering of 6.1 x 10-44<\/sup> cm2<\/sup> for a WIMP mass of 100 GeV, at the 90% C.L.
\nAfter successful filling of the DarkSide-50 detector with UAr in April 2015, about 70 days of dark matter WIMP search data were acquired and used to assess the capabilities of the UAr. While the general characteristics (including the high light yield) of the UAr remained similar when compared to the AAr, the reduction of the 39<\/sup>Ar content was better than expected, with a reduction factor of about 1400.
\nThe DarkSide Collaboration has just recently published the results of this UAr dark matter search, again showing no remaining backgrounds in the WIMP search region after all cuts. Combining these data with the AAr data, the sensitivity for spin independent WIMP-nucleon scattering is extended to 2 x 10-44<\/sup> cm2<\/sup> for a WIMP mass of 100 GeV, at the 90% C.L. These are the most sensitive results for a liquid-argon-based direct dark matter WIMP search to date.
\nThe DarkSide-50 detector has already provided valuable new scientific results, and successfully validated the basic background-free design concepts for the proposed DarkSide detectors of the near-future.<\/p>\n","protected":false},"excerpt":{"rendered":"

After a successful prototype (DarkSide-10) the first physics detector in the DarkSide program is\u00a0DarkSide-50 (DS-50), currently situated in\u00a0Hall C of […]<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":0,"menu_order":11,"comment_status":"closed","ping_status":"closed","template":"sidebar-page.php","meta":{"footnotes":""},"class_list":["post-32","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/darkside.lngs.infn.it\/index.php?rest_route=\/wp\/v2\/pages\/32","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/darkside.lngs.infn.it\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/darkside.lngs.infn.it\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/darkside.lngs.infn.it\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/darkside.lngs.infn.it\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=32"}],"version-history":[{"count":0,"href":"https:\/\/darkside.lngs.infn.it\/index.php?rest_route=\/wp\/v2\/pages\/32\/revisions"}],"wp:attachment":[{"href":"https:\/\/darkside.lngs.infn.it\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=32"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}