CERN expects
great revelations
The flagship of experimental physics, the
LHC accelerator at CERN in Switzerland, will
be formally opened in 2007. Scientists from
all over the world, including some from the
University of Bergen, have put an incredible
effort into planning the experiments.
The physics laboratory CERN (the European laboratory for particle
physics), which is situated outside Geneva, is the world’s largest
particle physics laboratory. For the last few years, they have been
building a new and more powerful particle accelerator: the Large
Hadron Collider (LHC). The power will be switched on sometime in
the second half of 2007 and the experiments will begin. Hopefully,
they will bring us a little closer to answering why the world is the
way it is.
The University of Bergen’s main involvement is in the work on
ATLAS, one of the four detectors to be installed in the 27-kilometre
long circular tunnel where the experiments will take place. The
University of Bergen has supplied some of the components for
the detector, and it has also taken part in the planning of the
experiments that are to be carried out. ATLAS is a general detector
intended to detect everything that happens when high energy
protons collide with each other.
Dark matter
Associate Professor Anna Lipniacka of the Department of Physics
and Technology is particularly interested in finding dark matter.
Dark matter is invisible matter which does not interact with the
visible world, but which still makes up almost a quarter of all
matter in the universe. The stars in our galaxy would be flung in all
directions had the dark matter not held them together.
"Only a very small part of the matter in the universe consists of
visible matter. We know that the dark matter must consist of heavy
particles that hardly react with anything, otherwise we would
already proven its existence. Using the LHC accelerator we will
hopefully be able to recreate the conditions of the Big Bang well
enough to create dark matter as well,” she hopes.
In addition to searching for dark matter, ATLAS will be used to
look for answers to other fundamental questions: Why do particles
have mass? Are there more dimensions? Are there so-called
supersymmetric particles?
Making the impossible possible
The protons which will collide come in small bunches that are
accelerated to a speed close to the speed of light. When the
experiments have started, there will be a collision 40 million times a
second, and the amount of data from the detectors will exceed the
sum of all telephone networks in the world. There are no computers
powerful enough to handle this. The solution to the problem is a
so-called GRID: The data will be sent to interconnected computers
all over the world, and each of these computers will process a part
of the data. The system is presently being tested by processingdummy data generated by a simulation program. These analyses
will result in dummy articles in preparation for the final articles
which must be written when the results from the experiments start
arriving.
Even though the amount of data is enormous, only a small part
of it, about one collision in a million, will be interesting enough
to be worth storing. The electronics associated with the detector
must therefore be capable of separating the interesting events
from the rest, and not store all the useless data which will be
produced by the detector. Still, the amount of data to be stored will
be equivalent to 1,200 CDs a minute. The GRID network must be
capable of processing this.
Counting down to start
In cooperation with other Nordic universities, the University of
Bergen has supplied some of the electronics. They compete with
the best in the world to produce and supply detector components,
and they have no choice but to deliver high quality. Despite the
fact that ATLAS will examine the smallest particles in the world,
the detector has to be the size of a five-storey house. ATLAS must
have time to measure the path, the energy and the charge of the
particles before they leave the detector. As ATLAS has grown,
people have had to put on climbing gear and take safety courses
to be able to work on its assembly. It is now being tested by
measuring cosmic radiation to make sure that all the parts function
as intended. The magnetic field around the detector, which will
steer the proton beams and ensure precise collisions, has also been
tested. In addition, great demands are made on the cooling system
used to cool down the magnets and make them superconductive. It
uses liquid helium, and is the largest of its kind in the world.
No one knows what this effort might help us reveal. But for the
physicists, excitement is growing day by day.
