Dark Matter Teacher Guide - Perimeter Institute

Figure 21 If dark matter is made of WIMPs or axions, then billions of
dark matter particles are passing through your body each second.
PICASSO Dark Matter Experiment
One of the experiments at SNOLAB is the PICASSO
(Project in Canada to Search for Supersymmetic Objects)
experiment (Figure 22), which is highlighted in the video.
It consists of millions of tiny droplets of superheated
liquid Freon (C 4 F 10 ) suspended in a gel. There is a very
small chance that a WIMP passing through the experiment
will collide with a fluorine nucleus within one of the
droplets. When this happens, energy is transferred to the
droplet, causing the liquid to vapourize and a tiny bubble
to form. The bubble then rapidly expands, sending out a
shock wave that physicists detect using acoustic sensors.
ICE CUBE Dark Matter Experiment
Another dark matter experiment is located at the South
Pole. The ICECUBE experiment consists of a vast array
of sensitive light detectors located in 1 km deep holes
in the ice. If dark matter is made of WIMPs, then dark
matter that is gravitationally trapped within the Sun and
Earth should, indirectly, cause light to hit the detectors in a
distinctive pattern.
CERN and the LHC
Yet another experiment that might detect dark matter is
taking place just outside Geneva, Switzerland at CERN, the
world’s largest particle accelerator (Figure 23). Using the
Large Hadron Collider (LHC), physicists hope to actually
create dark matter particles (WIMPs) via extremely highenergy
collisions between subatomic particles. If they
succeed, this will provide evidence for the WIMP theory
of dark matter.
Modifying Newton
A small minority of physicists advocate a radical solution
to the mystery of dark matter: modifying Newton’s theory
of universal gravitation on the scale of a galaxy (or larger).
One theory is called Modified Newtonian Dynamics
(MOND) and it can explain the mass discrepancy between
the Orbital and Brightness Methods. MOND does this
by altering the relationship between the magnitude of the
gravitational force F and distance r from
to
for very large distances.
Although MOND can explain the evidence supporting the
existence of dark matter within galaxies, it cannot explain
the evidence for it from gravitational lensing. In addition,
changing a basic physical law is a very rare occurrence in
physics and most physicists do not believe that this is the
solution to the mystery of dark matter.
Conclusion
The race to be the first to detect dark matter here on Earth
is intense. Whoever succeeds first will, for the first time
ever, have directly observed the particle that makes up, on
average, 90% of the mass of every galaxy in the universe.
They are almost certain to win a Nobel Prize.
Figure 22 PICASSO dark matter experiment in Ontario, Canada.
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