The Worshipful Company of Engineers The Swordsman Newsletter ...

The Swordsman Issue 29
On arrival, we were treated to an excellent lunch in the
staff restaurant before being welcomed into the main
auditorium for an explanation of the work or CERN
and, importantly, their outreach programme.
Everything they do at CERN is published freely and
they have a mission, as well as answering fundamental
questions, to inspire the next generation of physicist
and physics teachers. Our host was Mick Storr who
heads the outreach programme and has the distinction
of once sharing an office with Tim Berners-Lee, the
inventor of the Internet and another CERN scientist.
Mick (left) told us that
CERN has a budget of
CHF1Bn per year –
equivalent to a
medium sized
European university –
and is supported by 20
European states.
We were then taken to
see various parts of
the CERN facility,
guided by scientists
and engineers who are
engaged in the
experiments
themselves. A degree
in physics would have been useful to understand the
explanations so for those (like me) who didn’t quite
get the whole thing at the time, here’s my simple (I
hope) explanation (correct, I hope) of what the LHC is,
how it works, what they are looking for and why.
The objective of the LHC is to accelerate two streams
of protons (positively charged particles that are found
in the nuclei of atoms) to close to the speed of light
and then encourage them to run head-on into each
other. Other particles are expected to be formed as a
result of these collisions including, they hope, the
famous “Higgs Boson” and to detect those particles
when they are formed. So how do you accelerate a
charged particle? Easy – putting it in an electric field
will give it a shove – but to get it moving fast enough
for the kind of collisions they need requires a lot of
shoves so they are sent round in a circle and put
through the electric field repeatedly, rather as a
hammer thrower builds up speed in the hammer by
spinning round several times. In the LHC, two beams
of protons move in opposite directions in concentric
tubes 27km in circumference, buried under the Swiss
and French countryside and they actually go round
billions of times. How do you make them move in a
circle? Electrical engineers will remember that a
charged particle moving in a magnetic field
35
experiences a sideways force, so if giant
electromagnets are placed around the tubes they can
produce the inward force that keeps the protons
moving in a circle rather as the hammer thrower pulls
on the hammer until it’s time to let go. But these
protons are travelling at great speed so it needs a
powerful magnetic field to turn the protons by a small
amount, hence the electromagnets have
superconducting coils and the circle is 27km in
circumference
At the CMS Site
To get the beams to collide, they steer them towards
each other and focus them down so each is the
thickness of a human hair. Even then, the chance of
collision is small but there are so many of them that
they get about 600 million collisions per second. At
full speed, each proton has about the same energy as a
flying mosquito, which doesn’t sound like very much,
but considering the proton is a billion billion times
smaller than the mosquito, that’s quite a punch.
The detector, called a Compact Muon Solenoid (CMS)
comprises some more electromagnets that are wrapped
around the point of collision and which cause the
particles formed to travel in spirals in a solid-state
detector. The traces formed allow the physicists to
calculate the energy of the particles produced and they
then try to match the energies of those particles to the
energies of particles that theory predicts should exist.
If they get a match, that’s a piece of evidence that the
theory is correct. If not, then that’s equally interesting
(to a physicist, anyway). And the one they are looking
for is the famous “Higgs Boson”.
Our party was able to go underground to see (or at
least get close to) the point of collision and the CMS.
We were just in time because the area was about to be