15 February 2007

Dark matter and ‘God particle’ within reach

By
Agençe France-Presse
The boundaries of knowledge in particle physics look set to be broken soon with scientists around the globe locked in a multi-billion-dollar race to solve two great mysteries.
Dark matter and 'God particle' within reach

Scientists hope the world's most powerful atom smasher, the Large Hadron Collider in Geneva, will unlock the secrets of the elusive 'God Particle' when switched on later this year. Credit: CERN

PARIS: The boundaries of knowledge in particle physics look set to be broken soon with scientists around the globe locked in a multi-billion-dollar race to solve two great mysteries.

Their quest: find the secrets of dark matter and the ‘God particle’ – a sub-atomic particle that is fundamental to understanding the nature of matter, but so elusive that, physicists quip, it can only be compared to divinity.

Last week, an international consortium stepped up the pace by announcing in Beijing, China, a design for the world’s most expensive atom smasher – the US$6.7 billion (AU$8.6 billion) International Linear Collider (ILC).

In a double tunnel 31 kilometres long, particle physicists would collide electrons and their antimatter opposites, positrons, at energies of 500 billion electron volts.

The scheme – which could be extended to 50 kilometres and a trillion electron volts – will hurl these particles at close to the speed of light.

The resultant collision could unlock dark matter and dark energy, the invisible, enigmatic substances that together are thought to comprise 96 per cent of the mass of the universe.

Engineering studies for the ILC will start later this year with the idea of making a decision in 2010 on whether to press ahead with building the machine. If all goes well, ground will be broken in 2012 and the collider itself will be fired up at the end of the next decade.

“The ILC probably represents the maximum that can be achieved with this type of technology,” said Guy Wormser, head of France’s Linear Accelerator Laboratory, who took part in the Beijing meeting.

Scientists in the U.S. and Europe, meanwhile, are grappling to be first to detect the most eagerly-sought particle in physics – the Higgs Boson. Construed in the 1960s by a British physicist, Peter Higgs, the Boson is thought to exist in an all-pervading field, giving all other particles their mass.

If the Higgs exists, it would fill a worrying gap in the Standard Model, the century-old notional structure for describing the fundamental nature of matter. But if the Higgs doesn’t exist, it will be back to the drawing board.

The Europeans are months away from switching on the world’s most powerful smasher, the Large Hadron Collider (LHC), which is being built at the European Centre for Nuclear Research (CERN) near Geneva, Switzerland, using a 26-kilometre underground ring.

The LHC will whizz protons, which are far heavier particles than electrons, to energies of up to 14 trillion electron volts.

Until a few months ago, it seemed that the prize of the Higgs would almost certainly go to the LHC. It alone had the power to explore the theorised particle’s mass, which was deemed to be a maximum of 166 giga-electron volts (GeV).

But researchers at the Tevatron collider, at the famous Fermilab facility near Chicago in the U.S., believe they could be in with a chance. New calculations suggest that the upper limit for the Higgs is 153 GeV, which is within the Tevatron’s range.

Meanwhile, physicists at Stanford University in California said they have conducted an experiment that proves the viability of a low-cost collider technology called a plasma accelerator.

Instead of using a giant magnet and a huge tunnel to accelerate the particles, their accelerator uses a tunnel just three kilometres long to speed up a beam of electrons.

By passing the electrons through a cloud of ionised gas, or plasma, that is just one metre across, the team were able to double the particle’s energy – a massive booster effect, they report in the British journal Nature.

Only a tiny fraction of the electrons in the beam were accelerated this way, though, and the beam itself is not ‘concentrated’ enough to get a good yield of particle collisions.

According to Wormser, “Plasma accelerators are a promising technology and may be the solution for the future, but on a timescale of 20 to 25 years at least.”

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