Underground search for 'God particle'
By Paul Rincon
At the foot of the Jura Mountains, where Switzerland
meets France, is a laboratory so vast it boggles the
mind.
But take a drive past the open fields, traditional
chalets and petite new apartment blocks and you will
look for it in vain.
To find this enormous complex, you have to travel
beneath the surface.
One hundred metres below Geneva's western suburbs is a
dimly lit tunnel that runs in a circle for 27km (17
miles).
Nature is much smarter than us. It might come up with
a real surprise and that would be much more
interesting - much more satisfying
Professor Jim Virdee, Imperial College London
The tunnel belongs to Cern, the European Centre for
Nuclear Research. Though currently empty, over the
next two years an enormous experiment will be
installed here.
The Large Hadron Collider (LHC) is a powerful and
impossibly complicated machine that will smash
particles together at super-fast speeds in a bid to
unlock the secrets of the Universe.
'New physics'
By recreating the searing-hot conditions fractions of
a second after the Big Bang, scientists hope to see
new physics, discover the sought-after "God particle",
uncover new dimensions and even generate mini-black
holes.
When completed, two parallel tubes will carry
high-energy particles called protons in opposite
directions around the tunnel at close to the speed of
light.
The tunnel's huge circumference provides only the
slightest of bends. Nevertheless, around 5,000
superconducting magnets are needed to steer and focus
the particles around the tubes.
"When the coils are energised there is one jumbo jet -
500 tonnes - per metre pushing outwards," says LHC
project leader Lyn Evans.
Along the way, the proton beams will pass through
enormous experimental instruments called detectors
where they will cross.
When some of these protons collide at high energy,
heavier particles can appear amongst the debris.
Great quest
When the LHC is turned on in the latter half of 2007,
physicists will scour this crash wreckage for signs of
the Higgs boson.
The Higgs is nicknamed the God particle because of its
importance to the Standard Model, the theory devised
to explain how sub-atomic particles interact with each
other.
The 16 particles that make up this model (12 matter
particles and 4 force carrier particles) would have no
mass if considered alone. So another particle - the
Higgs boson - is postulated to exist to account for
this omission.
"The Standard Model is the best thing we've come up
with so far," says Jim Virdee, spokesman for the team
working on the Compact Muon Solenoid (CMS) detector.
But everyone recognises it is merely a stage on the
way to something else. The Standard Model describes
ordinary matter and yet astronomical observations show
this makes up but a small part of the total Universe.
Needless to say, new theories are gaining ground and
discoveries at the LHC could lead physicists towards a
unified theory to explain how the Universe works.
"We are at a stage where the theorists do not know
which direction to go in. The results from [our]
experiment will determine which direction science
takes," says Professor Virdee, who is based at
Imperial College London, UK.
"We don't always like theorists to tell us what we
should find. Nature is much smarter than us.
"It might come up with a real surprise and that would
be much more interesting - much more satisfying."
Huge scale
The detectors at the LHC will count, trace and analyse
the particles that emerge from the collisions between
protons.
To call them experiments simply does not give an idea
of their scale. The equipment weighs tens of thousands
of tonnes and in some cases is as tall as a
multi-storey building.
This week marked the inauguration of the enormous
cavern at Cessy in France that will house the CMS. A
78m-long shaft leads up to the surface, through which
the CMS will be lowered by crane early next year.
Both the CMS and its rival experiment, Atlas, are
based on a cylindrical "onion" structure with several
layers to perform different roles.
By 2010, nearly one billion collisions will take place
every second in these detectors.
"CMS needs to collect a sample of several hundred
collisions out of 40 million. And we have just three
microseconds to decide whether a collision produced
something interesting," Professor Virdee told the BBC
News website.
High energy
After attending the CMS inauguration, we travelled
just across the border to Switzerland, where the Atlas
cavern is located.
Measuring 53m long, 30m wide and 35m high, it is
taller than Canterbury Cathedral and is currently
empty but for the support structures that will hold
the detector in place.
"You're visiting at a good time; it won't look like
this again," says Atlas technical co-ordinator Mark
Hatch.
High radiation levels when the LHC is running mean
access to these caverns will be forbidden when the
machine is in operation, creating problems for the
scientists.
The energies achieved by the experiment are 70 times
greater than those of the Large Electron-Positron
Collider (LEP) which previously occupied the tunnels
at Cern.
Only by raising the bar will scientists be able to
expand our current understanding of the Universe.
Whatever the discoveries ahead for physicists working
at the LHC, the experiments will, according to its
chief scientific officer, Jos Engelen, "keep
physicists off street corners for a long time to come".
