Friday, January 30, 2015
YOLO COUNTY NEWS
99 CENTS

Team crosses off dark matter particle candidates

By
From page A7 | December 11, 2013 |

Results from the first run of the Large Underground Xenon experiment, operating a mile underground in the Black Hills of South Dakota, have proven the detector’s sensitivity and ruled out some possible candidates for a dark matter particle.

Initial results from 85 days worth of accumulated data were announced last month at a seminar at the Sanford Underground Research Facility in Lead, S.D.

“LUX is already producing the world’s best results and excluding parameter space for a dark matter particle,” said Matthew Szydagis, a postdoctoral researcher at the UC Davis department of physics. Szydagis is responsible for coordinating data analysis among the members of the LUX team.

Mani Tripathi, a UCD physics professor, is one of the seven founding principal investigators who proposed the LUX experiment in 2006. “We are finally seeing the fruits of our labor after these many years,” he said.

Dark matter is the most abundant form of matter in the universe but has so far been inferred only by its gravitational effects on light from distant galaxies and clusters of galaxies.

The leading theoretical candidates for a dark matter particle are WIMPs, or weakly interacting massive particles — so-called because they are postulated to interact ever so feebly with ordinary matter.

LUX was designed to have greater sensitivity to detect WIMPs than any other existing experiment. Recently, other researchers using ultra-cold silicon detectors reported three candidate WIMP events. However, these WIMPs would have produced more than 1,600 events in LUX’s much larger detector, or one every 80 minutes in the recent run. No such signals were seen.

“This is only the beginning for LUX,” said Dan McKinsey, a physicist at Yale University and co-spokesperson for the project. “Now that we understand the instrument and its backgrounds, we will continue to take data, testing for more and more elusive candidates for dark matter.”

In both theory and practice, collisions between WIMPs and normal matter are rare and extremely difficult to detect, especially because a constant rain of cosmic radiation from space can drown out the faint signals.

That’s why LUX is searching for WIMPs 4,850 feet underground in the Sanford Lab, where few cosmic ray particles can penetrate. The detector is further protected from background radiation from the surrounding rock by immersion in a tank of ultra-pure water, which was designed and instrumented by the UCD team.

At the heart of the experiment is a 6-foot-tall titanium tank filled with about a third of a ton of liquid xenon, cooled to minus 150 degrees Fahrenheit. If a WIMP strikes a xenon atom, it recoils from other xenon atoms and emits photons (light) and electrons.

The electrons are drawn upward by an electrical field and interact with a thin layer of xenon gas at the top of the tank, releasing more photons.

Light detectors in the top and bottom of the tank are each capable of detecting a single photon, so the locations of the two photon signals — one at the collision point, the other at the top of the tank — can be pinpointed to within a few millimeters. The energy of the interaction can be precisely measured from the brightness of the signals.

Installed in the summer of 2012, the experiment was filled with liquid xenon in February, and its first run of three months was conducted this spring and summer, followed by intensive analysis of the data. The dark matter search will continue through the next two years.

The Sanford Lab is a state-owned facility, and the U.S. Department of Energy supports its operation. The LUX scientific collaboration, supported by the National Science Foundation and DOE, includes 17 research universities and national laboratories in the U.S., the United Kingdom and Portugal.

UCD physicists contributed strongly to all aspects of LUX: design, construction, installation, commissioning, calibration, operations and data analysis.

Electronics engineer Britt Holbrook, and graduate students Mike Woods and Sergey Uvarov, played leading roles in the areas of electronics and computing. Mechanical engineer John Thomson and graduate student Jeremy Mock oversaw the installation of mechanical supports and the tricky move of the assembled detector to the underground lab.

The group was a leader in simulations, with key contributions from Szydagis, and graduate students Melinda Sweany and Nick Walsh. About 20 UC undergraduates have worked on LUX over the past seven years.

Planning for the next-generation dark matter experiment at the Sanford Lab already is under way. Compared to LUX’s third of a ton of liquid xenon, the LUX-ZEPLIN, or LZ, experiment would have a 7-ton liquid xenon target inside the same 72,000-gallon tank of pure water used by LUX and a sensitivity about a thousand times higher.

LUX and LZ are among 14 active research groups at the Sanford Lab. Other teams of researchers are planning experiments in physics, geology and biology that could extend the future of the lab for decades.

— UC Davis News

Comments

comments

  • Recent Posts

  • Enter your email address to subscribe to this newspaper and receive notifications of new articles by email.

  • .

    News

    Suspected Ebola patient being treated at UCD Med Center

    By San Francisco Chronicle | From Page: A1

     
    Town hall focuses on Coordinated Care Initiative

    By Anne Ternus-Bellamy | From Page: A1

    Schools give parents tools to help kids thrive

    By Enterprise staff | From Page: A1 | Gallery

     
    Need a new best friend?

    By Enterprise staff | From Page: A2 | Gallery

     
    Stanford University to get $50 million to produce vaccines

    By The Associated Press | From Page: A2

    Two more cases of measles in Northern California in children

    By The Associated Press | From Page: A2

     
    Dartmouth bans hard liquor

    By New York Times News Service | From Page: A2

     
    Vote for your favorites in Readers’ Choice poll

    By Enterprise staff | From Page: A3

    No bare bottoms, thanks to CommuniCare’s Diaper Drive

    By Special to The Enterprise | From Page: A3 | Gallery

     
    Storyteller relies on nature as his subject on Saturday

    By Enterprise staff | From Page: A3

    Still time to purchase tickets for DHS Cabaret

    By Enterprise staff | From Page: A3

     
    All voices welcome at sing-along Wednesday

    By Enterprise staff | From Page: A3

    Great Chefs Program will feature Mulvaney

    By Special to The Enterprise | From Page: A3

     
    Walkers head out three times weekly

    By Enterprise staff | From Page: A3Comments are off for this post

    Free tax preparation service begins Monday

    By Special to The Enterprise | From Page: A3

     
    February science fun set at Explorit

    By Lisa Justice | From Page: A6 | Gallery

     
    Take a photo tour of Cuba at Flyway Nights talk

    By Enterprise staff | From Page: A6 | Gallery

    See wigeons, curlews and meadowlarks at city wetlands

    By Special to The Enterprise | From Page: A8 | Gallery

     
    .

    Forum

    Time for bed … with Grandma

    By Creators Syndicate | From Page: B5

     
    Weigh quality of life, density

    By Letters to the Editor | From Page: A10

    Olive expert joins St. James event

    By Letters to the Editor | From Page: A10

     
    We’re grateful for bingo proceeds

    By Letters to the Editor | From Page: A10

    Tom Meyer cartoon

    By Debbie Davis | From Page: A10

     
    A ‘new deal’ for the WPA building

    By Special to The Enterprise | From Page: A10

     
    Protect root zone to save trees

    By Letters to the Editor | From Page: A10

    .

    Sports

    UCD men set new school D-I era win record

    By Bruce Gallaudet | From Page: B1 | Gallery

     
    UCD has another tough football schedule in 2015

    By Enterprise staff | From Page: B1

    Gould’s influence felt mightily in recent Super Bowls

    By Bruce Gallaudet | From Page: B1

     
    Mustangs hold off UCD women

    By Enterprise staff | From Page: B1 | Gallery

    Sharks double up Ducks

    By The Associated Press | From Page: B2 | Gallery

     
    Sports briefs: Watney, Woods start slow at TPC Scottsdale

    By Enterprise staff | From Page: B2

    Recall that first Aggie TV game, national title?

    By Bruce Gallaudet | From Page: B8 | Gallery

     
    .

    Features

    .

    Arts

    ‘Song of the Sea’ is an enchanting fable

    By Derrick Bang | From Page: A11 | Gallery

     
    ‘Artist’s Connection’ launches on DCTV

    By Special to The Enterprise | From Page: A11

     
    Gross’ paintings highlight a slice of Northern California

    By Enterprise staff | From Page: A12 | Gallery

    February show at YoloArts’ Gallery 625 is ‘Food for Thought’

    By Special to The Enterprise | From Page: A12 | Gallery

     
    .

    Business

    .

    Obituaries

    .

    Comics

    Comics: Friday, January 30, 2015

    By Creator | From Page: A9