July 2019    
         
         
 
     
     
  Dark matter dawdler  
     
     
  UChicago and Fermilab physicists propose using the Large Hadron Collider to detect "slow" dark particle.  
     
     
   
 
     
  So far, scientists have been able to make only indirect measurements and simulations of dark matter, such as the visualization above. (Image courtesy Zarija Lukic/Berkeley Lab)  
     
 
     
     
  Dark energy and dark matter --two of the greatest mysteries in physics--make up more than 95 percent of the universe, but scientists know they exist only from their influence on what we can observe. We know there's dark matter because we can see its gravitational effects (it helps keep galaxies from flying apart), but no one has detected it directly.  
     
     
  UChicago physicist LianTao Wang, who studies how to find signals in large particle accelerators, and two Fermilab scientists have devised a method for stalking dark matter in the Large Hadron Collider (LHC).  
     
     
  Theorists think there's one particular kind of dark particle that only occasionally interacts with normal matter. Compared to other known particles, it would be heavier and longer-lived, with a lifetime of up to one-tenth of a second. For reference, the Higgs boson--the last holdout particle in physicists' grand theory of how the universe works until it was discovered at the LHC in 2012--has a lifetime of less than a sextillionth of a second. (A sextillionth is 10^-21. The Higgs boson's lifetime is actually ~10^-22 seconds, but there's no name for that.)  
     
     
  These dark particles may actually be coupled to the Higgs boson in some fashion. Perhaps the Higgs is "a portal to the dark world," said Wang. "It's possible that the Higgs could actually decay into these long-lived particles."  
     
     
   
 
     
  The Compact Muon Solenoid (CMS) is a general-purpose detector at the Large Hadron Collider. (Photo courtesy CERN)  
     
 
     
     
  Several times a decade, researchers believe, these hypothetical particles could get caught up in proton collisions--more than a billion per second--that the LHC is constantly creating and measuring.  
     
     
  Each collision sends subatomic chaff spraying in all directions. The challenge is isolating the signal of the potential dark particle, so Wang's team proposed exploiting its slightly slower speed.  
     
     
  "If it's that heavy, it costs energy to produce, so its momentum would not be large--it would move more slowly than the speed of light," said Jia Liu, a postdoc and first author on the study.  
     
     
  That nanosecond time delay would set it apart from the other particles. To find the dark matter candidate, scientists would only need to tweak the system to look for particles that are produced and then decay more slowly than everything else.  
     
     
  LHC already has detectors sophisticated enough to catch this difference. A recent study using data from the last run found the method should work--plus the detectors will get even more sensitive as part of an upgrade now underway that will boost its luminosity tenfold.--Louise Lerner  
     
 
 
 
     
  Dark matter matters  
     
     
 
     
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Why haven't we found dark matter yet?
 
     
     
     
     
 
     
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University of Michigan physicist Katherine Freese, PhD'84, suggests using ancient minerals as dark matter detectors.
 
     
     
     
     
 
     
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The only experiment claiming to have detected dark matter faces major controversy.
 
     
     
     
     
 
     
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On October 31, 2019, dark matter experts and enthusiasts will celebrate around the world. Plan your own Dark Matter Day event or find one to join.
 
     
 
     
 
         
         
    Spotlight    
         
         
 
     
     
  Warped space-time  
     
     
   
 
     
  The Fabric of the Universe art installation ran from March through November 2018 at the Adler Planetarium. (Photo courtesy Arts, Science + Culture Initiative)  
     
 
     
     
  In 2014 Benedikt Diemer, PhD'15, then a UChicago grad student in computational astrophysics, and Isaac Facio, then an MFA candidate in Fiber and Material Studies at the School of the Art Institute of Chicago, created an art collaboration called The Fabric of the Universe.  
     
     
  As part of UChicago's Arts, Science, and Culture Initiative Graduate Collaboration Grants program, which pairs science and art students for interdisciplinary research, they built a physical, 3D, textile-based representation of dark matter in the universe.  
     
     
  The installation was based on a computer simulation that modeled a billion virtual dark matter particles. Diemer and Facio used a cotton and polyester/fiberglass blend woven on a Jacquard loom to form the filaments and nodes of the cosmic webOver the last three years, the installation has been shown at the Non-Fiction Gallery in Savannah, Georgia, and the Sullivan Galleries and Adler Planetarium in Chicago.  
     
 
 
     
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