by Mark Henderson
August 7, 2009
Large Hadron Collider will run at
only half its maximum energy when it restarts in November after a
serious fault forced it to be shut down for more than a year.
Officials from the CERN particle physics laboratory in Geneva
announced last night that it will be 2011 before the world’s most
powerful atom-smasher reaches its full capacity.
While the £4 billion “big bang machine” should eventually be capable
of running at an energy of 7 tera-electronvolts (TeV),
it will operate initially at just 3.5 TeV when it starts smashing
protons together in mid-November. The first science results
are expected a few weeks later.
It will move up to higher energies only once engineers are confident
that it is safe to do so, and it will reach maximum power only after
it is shut down for a refit in the winter of 2010-11.
The lower-energy first run will still allow scientists to use the
collider to search for the
Higgs boson - the elusive “God
particle” that is proposed to give matter its mass - and to
investigate other new aspects of physics.
It will take longer to collect the data needed for these
experiments, however, increasing the chances that evidence for the
Higgs boson might first be found by the less powerful
Tevatron accelerator at Fermilab in
the United States.
“We’ve selected 3.5 TeV to start
because it allows the LHC operators to gain experience of
running the machine safely while opening up a new discovery
region for the experiments,” said Rolf Heuer, CERN’s
James Gillies, CERN’s head of
communications, said an energy of 3.5 TeV would allow operators to
gain experience with the machine at lower energies, without
seriously compromising the LHC’s ability to investigate new physics.
“The decision had already been taken
not to run at over 5 TeV, and the question was, do you lose
anything in terms of physics by running at 3.5 TeV rather than
5? It still gives you the same access to new physics, but it
will just take longer to get there. We don’t lose sensitivity to
the Higgs, or to
Even at 3.5 TeV, the LHC will still be
significantly more powerful than the Tevatron, which operates at a
maximum of 1 TeV, and is still in pole position to find the Higgs
boson in spite of the delays.
While the Tevatron has established a mass range for the Higgs boson,
it will be capable of finding it only if it its mass lies in a
narrow band. The LHC should find it whatever its mass, even running
at half its maximum capacity.
The first beams were injected into the LHC on September 10 last
year, but nine days later a connection between two magnets failed.
This caused a huge leak of the helium that cools the 17-mile (27km)
ring around which protons will be fired against one another at
99.9999991 per cent of the speed of light.
The leak inflicted further damage and the accelerator was mothballed
so that 53 magnets could be replaced. Engineers have since found and
replaced other magnet connections that could have been at risk of
causing a repeat of the fault, and installed other safety features
to prevent another fault.
CERN announced earlier in the year
that it would run the LHC throughout the winter at an extra cost of
about £13 million, to make up for the delay. The accelerator would
normally be shut down over the winter for maintenance and to save on
Once engineers have more experience with running the LHC at 3.5 TeV,
the energy will be increased towards a maximum of 5 TeV next year.
At the end of 2010, it will also be used to collide lead ions for
the first time, so that the Alice experiment can study quark-gluon
plasma, a state of matter thought to have existed immediately after
the Big Bang. The LHC will then shut down at the end of 2010, so
that further modifications can be made to allow the machine to run
at 7 TeV.
Dr Heuer said:
“The LHC is a much better understood
machine than it was a year ago. We can look forward with
confidence and excitement to a good run through the winter and
into next year.”