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Last Updated: Monday, 29 November, 2004, 10:37 GMT
Device to probe limits of physics
Atlas SCT barrel, University of Oxford
Atlas will probe the fundamental nature of the Universe
UK physicists have completed the first crucial element of an experimental device designed to probe the forces that shape our Universe.

The Atlas experiment will explore the fundamental properties of matter and look for "new physics" beyond the limits of our current understanding.

It will be housed at the Large Hadron Collider (LHC) particle accelerator, due to begin operating in 2007.

The LHC could create mini-black holes as particles collide at high energies.

There has to be new physics in this energy region
Dr Tony Weidberg, University of Oxford
And researchers are confident they will be able to detect the most sought after particle in physics: the Higgs boson, which explains why all other particles have mass.

The finished element is the first of the four barrels that will form the central part of the SemiConductor Tracker (SCT).

When complete, Atlas will be 25m high (as tall as a five-storey building), 46m long and will weigh about 7,000 tonnes.

The SCT will track the movement of particles as they pass through the thousands of silicon wafers with which the barrels are populated.

Smash it up

Out of nearly 1,000 million collisions every second, only a few will have the special characteristics that might lead to new discoveries.

"[Atlas] has taken 10 years to plan, 10 years to build and it will take another 10 years for us to exploit the data," says Georg Viehhauser an Atlas team member at the University of Oxford.

Atlas will sit inside a mammoth underground cavern (Cern)
Atlas will sit inside a mammoth underground cavern
The LHC, which will house the Atlas experiment, is a giant "atom-smasher" that is being built at Cern, on the Swiss-French border, to replace the now defunct Large Electron-Positron Collider (LEP).

The LHC will occupy the underground tunnel (27km in circumference) built to house the LEP.

Scientists will use the LHC to accelerate beams of protons in opposite directions at energy levels seven times higher than has been achieved before in an accelerator.

The head-on collision of these particles not only replicates the conditions that existed just moments after the Big Bang, it generates other particles that can tell scientists more about the nature of the Universe.

SCT barrel, University of Oxford
Four barrels will form the central part of the SCT
It is hoped that by stepping up to a higher energy level, these collisions will produce heavier particles that could not be detected in previous particle accelerator experiments.

"There has to be new physics in this energy region," said Dr Tony Weidberg, of the University of Oxford. "That's the real motivation for the LHC."

One of these proposed new areas of physics is the theory of supersymmetry.

Under the so-called standard model of physics, all fundamental particles fall into two groups: fermions that make up matter and bosons that exchange the forces acting on matter.

Partner search

In supersymmetry, every fermion has a so-called "superpartner" which is a boson, and every boson has a fermion superpartner.

"We haven't seen any of the supersymmetric partners yet, and one explanation for this is that these partners have to be heavy," Dr Weidberg explained.

Computer-generated image of the LHC tunnel (Image: Cern)
The accelerator will sit inside the old LEP tunnel
Supersymmetry may also be able to explain the nature of dark matter, he added, which astronomers say makes up about 25% of the Universe.

Finding the Higgs boson will be seen as a priority for the new LHC and Atlas, because it is fundamental to a complete understanding of matter.

The Higgs boson is required to validate the so-called Standard Model of physics, the most established framework devised to explain the nature of fundamental particles and their interactions.

The theory is that all particles acquire their mass through interactions with an all-pervading field, called the Higgs field, which is carried by the Higgs boson.

Some physicists have made an even more startling prediction about the LHC: that it is energetic enough to create mini-black holes.

SCT barrel, University of Oxford
Hundreds of silicon detectors cover the barrel
"Mini-black holes are much more interesting than big black holes," Dr Weidberg explained.

Dr Viehhauser explained: "Mini-black holes are being created around us anyway, but maybe at a very low rate and that's why we can't do physics with them."

The ability to produce such exotic effects within a particle accelerator should allow physicists to test key theories of quantum mechanics.

But Dr Weidberg admits that scientists will have to trawl through a sea of data in their search for a handful of interesting events.

"It's like trying to find a needle in a haystack from a train moving at 100 miles/hour," he said.

The LHC is expected to generate a whopping 10 petabytes of data every year. This is roughly equivalent to the storage capacity of 10 million CDs.

In order to process such a large amount of data, the scientists will have to make use of Grid Computing. The Grid harnesses computers around the world for their processing power.

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10 Mar 04 |  Science/Nature

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