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High energy physics at the LHC

Tom Feilden | 07:19 UK time, Tuesday, 30 March 2010

Large Hadron Collider

At Last. After 25 years, and more than £6bn, the Large Hadron Collider is finally ready to do some serious physics.

If all goes according to plan, at a little after 8 o'clock this morning, the gates will come down and two streams of protons travelling in opposite directions around the 27km LHC tunnel will collide head-on. A new era of particle physics will begin.

At 7 TeV, or tera-electron-volts, the collision energy of that impact will dwarf anything mankind had engineered before. To give you some idea what it means, imagine focussing all the pent-up energy of a battleship ploughing forwards at full speed into a stream thinner than a human hair, accelerating it to nearly the speed of light, and then smashing it straight into another one coming the other way.

At these colossal energies the normal, everyday, rules of atomic physics break down. The protons hurtling around the LHC will be smashed to pieces, revealing their constituent parts - and that's what the scientists are looking for.

Straddling the LHC at the key points where the beams cross sit four giant experimental detectors which will monitor the collisions for the tell-tale signs of the elusive Higgs Boson (the particle that conveys mass to all the others), extra dimensions in space-time, and the particles that make up dark matter.

Right now the banks of electronic screens that run around the Data Detection and Analysis Centre for the Compact Muon Solenoid, or CMS, experiment are recording only the passage of an occasional cosmic ray through the detector. But when the collisions start, Guido Tonelli, says thousands of tracks should spiral out from the centre.

"Very soon we'll see events originating in the centre of the detector, with tracks bursting out from the inter-action region. We expect to see hundreds, thousands, of tracks coming out from the collisions. It will be incredibly exciting".

One of the first questions the LHC could resolve concerns an idea the theoretical physicist John Ellis has spent the best part of 25 years developing. Super Symmetry is an elegant explanation for the fundamental structure of the universe that avoids the messy complexity of extra dimensions implicit in ideas like string theory.

It's a fantastically exciting moment. We theorists have been speculating for most of our careers about the fundamental structure of the universe. Finally we're going to start seeing what nature has in store for us.

In a sense it doesn't really matter what the the LHC uncovers - whether it's the Higgs Boson, or something completely new. Whatever the tracks emanating from the centre of the detectors reveal will offer a profound insight into the fundamental structure of matter, and take us closer to a unified theory of everything.

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