To help scientists uncover the secrets of dark matter, archi- tects and engineers with LEO A DALY are heading a mile underground, retrofitting part of an abandoned gold mine
into one of the most specialized cleanrooms on earth.
The Sanford Underground Research Facility (SURF) is a
sprawling complex of underground labs that occupies the former
Homestake gold mine in Lead, South Dakota. Here, shielded by
a mile of rock from the interfering radiation that bombards the
earth, chemist Ray Davis, Jr., performed the first solar neutrino
experiments. These experiments, conducted from 1970 to 1994,
earned Davis a share of the 2002 Nobel Prize in Physics.
That same cavern—located 4,850 feet underground—is now
part of the Davis Campus, and is being adapted to conduct the
next generation of dark matter experiments. In an unprecedented
collaboration known as LUX-ZEPLIN (LZ), a consortium of 250
scientists and 37 institutions will use the most sensitive detector
on earth and 20 percent of the world’s annual production of liquid
xenon to directly detect Weakly Interacting Massive Particles
(WIMPs). Scientists believe these hypothetical particles could
help explain the nature of dark matter, which comprises about 85
percent of the mass in the Universe.
Dark matter is so named because it does not emit or absorb light.
However, it leaves clues about its presence via gravity. It can be
observed affecting the orbital velocities of galaxies in clusters, and
distorting light emitted from background objects in a phenomenon
known as gravitational lensing. WIMPs pass through ordinary matter leaving hardly a trace, but under the right circumstances, they
may affect observable changes in noble elements such as xenon.
The most sensitive piece of equipment on earth
The LZ experiment will take place in a tank full of 10 tons of
liquid xenon. Theoretically, as an impinging flux of dark matter particles (WIMPs) pass through the tank, the xenon nuclei will recoil
in response to collisions. A recoiling xenon nucleus causes a flash of
scintillation light, liberating a charge that causes electroluminescence
when extracted from liquid into xenon gas. In the LZ’s Time Projection Chamber (TPC), these flashes of light will be detected by 494
photomultiplier tubes, deployed above and below the liquid xenon.
These photomultipliers convert the flashes of light to data so they
can be observed by scientists.
Building a Cleanroom
in an Old Gold Mine
A cavern that was home to the first solar neutrino experiments in
1970 is now being adapted to conduct the next generation
of dark matter experiments.
by Steven Andersen, AIA, Senior Architect, LEO A DALY
Photomultiplier tubes at the top of the LUX detector, which is the precur-
sor to the LZ experiment. Photo: Matthew Kapust, Sanford Underground
The walls of the Davis Lab are carved out of rock and covered in shot-
crete. Photo: Matt Kapust, Sanford Underground Research Facility