You may have heard the term ‘Dark Matter’ without a convincing explanation of what it actually is;
that is because no-one really knows!
Many astronomical observations have shown effects 
that cannot be explained by the matter that we see around us.
For example, galaxies seem to be rotating too fast,
which suggests that they contain a large amount of 
extra matter that does not emit or absorb light.
The effect of this new type of “dark matter” 
can also be seen in larger systems
and in fact galaxies probably 
couldn’t have formed without it.
Our observations show that there is 
five times more dark matter in the universe
than the ordinary visible matter
that we are made of.
Many of us here at the Institute for
Particle Physics Phenomenology in Durham
are working to try and understand exactly what it is, 
and to see it directly interact with normal matter.
One thing that we do know about dark matter
is that any interaction it has with ordinary
matter must be very rare, so we have to build
incredibly sensitive experiments.
One example of such an experiment is SuperCDMS, 
of which we have a model,
where the white plastic disks represent, 
and are the same size as, 
the metallic crystals that will be used.
SuperCDMS will begin collecting data in Canada in the 
early 2020s and it is sensitive enough to detect
one nucleus recoiling after 
a dark matter particle has hit it,
due to the vibrations this causes in 
the Germanium crystal lattice.
In order to be this sensitive, 
SuperCDMS must be kept at a chilly minus 273°C.
We can use computer simulations to model potential
types of dark matter and design the experiment
to increase our chances of a discovery.
An added difficulty is that the vibrations can also be 
caused by normal matter, and since
we aren’t interested in these results we call them 
‘background events’.
Again, we can use computer simulations to study the
expected background events 
for different experimental designs.
These background events are caused
by the natural radiation that surrounds us.
It comes from the atmosphere above us,
the rocks below us
and bananas.
If we tried to run the experiment in this room
we would only see background events, 
here represented by red lights.
In order to see the dark matter, the blue flashes,
we need to stop this radiation reaching our detector.
We can start by going underground 
so that the ground above absorbs radiation.
Going further underground will
reduce the atmospheric radiation even more, 
but there is a practical limit.
The deeper we go the more difficult, 
and expensive, it becomes.
SuperCDMS will be placed in a particle
physics laboratory called SNOLAB, 
2 km underground.
We also need to stop radiation 
from the rocks in the earth’s crust
so we place shielding
around the entire experiment.
SuperCDMS will have layers of lead, polyethylene 
and water with a total width of 2m.
As with going further underground, 
adding more shielding would be better, but expensive.
The high cost of the shielding is partially due to 
needing to use very pure materials,
which contain as few radioactive atoms as possible.
The current technological level allows us to have a purity
of about one part in a thousand,
meaning the materials are one thousand times 
less radioactive than they were originally.
With each additional step to our design 
we have seen fewer red flashes.
This is great news as it shows how much
we’ve reduced the background radiation.
Now we just need to spend five years
 watching our experiment
and count the blue flashes.
Here we are lucky,
and we can ‘time warp’ through the five
years and analyse our results.
We still have background events in our detector
as we can’t block out every single bit of radiation.
We can again use computer simulations
to tell us that an incoming particle interacting
with an electron rather than a nucleus, interacting
on the surface of the detector or interacting
in more than one detector is far more likely
to be normal matter than dark matter,
so we can ignore such events.
After the experiment has run the data will
be analysed, and if dark matter has been detected
we can determine its mass and 
the probability that it will interact.
This measurement would only be the start though - 
the real task will then be to
determine what this particle actually is 
and how it relates to the rest of the known matter.
And once again, computer simulations will be our guide!
The search for dark matter, 
like most research, is a bit like the search
for a needle in a haystack,
without the guarantee that there is one to find!
But research is about developing methods
 to search systematically,
and these methods, and the insights 
that we gain along the way,
be it technological advancements in cryogenics, 
electronics and computer science 
or unexpected discoveries
help make it worth it.
One day these discoveries may have applications that haven’t even occurred to us yet.
