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A Large Ion Collider Experiment, or ALICE

A Large Ion Collider Experiment, or ALICE, (pictured above) recorded the first results from a proton-proton collision inside the Large Hadron Collider, physicists announced in December 2009.

Picture by Maximilien Brice, copyright CERN

Ker Than

National Geographic News

Published December 7, 2009

The Large Hadron Collider (LHC) is quickly making up for lost time: The first scientific results from the recently restarted particle accelerator have been announced—about two weeks ahead of schedule.

During the first collisions of the LHC's twin beams of protons, a machine called A Large Ion Collider Experiment, or ALICE, collected the results from a proton-proton smashup.

Protons are positively charged subatomic particles found in the nuclei of atoms. Colliders such as the LHC are designed to crash such particles together so that they break apart into even more basic components, offering scientists a glimpse of the fundamental building blocks of matter.

For the Large Hadron Collider's first result, ALICE found that a proton-proton collision recorded on November 23 created the precise ratio of matter and antimatter particles predicted from theory.

The collision occurred at the lowest energy possible in the LHC—each beam had just 450 billion electron volts (GeV), creating a 900 GeV collision.

"Collisions at 900 GeV have only been measured with protons and antiprotons. They've never been measured with two protons," said David Evans, a physicist at the U.K.'s University of Birmingham and head of the ALICE project.

The results show "that we understand our detector," Evans said, "so when we go to higher-energy collisions where we don't know what the answers should be, we can better trust our results."

LHC Gets Closer to "God Particle"

At the Large Hadron Collider's current rate of activity, higher-energy collisions should occur before February 2010 and perhaps even before Christmas, Evans said.

The LHC is capable of collisions at 14 trillion electron volts (TeV), but some of the machine's most extraordinary discoveries could be made at much lower energy levels.

For example, scientists predict that the long-sought Higgs boson, sometimes called the God particle, could be discovered in the one to three TeV range.

"If we go to higher energies in February, there is a good chance the Higgs will be found," Evans said.

But after months of delay due to the LHC's electrical malfunction last year, Evans and his colleagues are greeting the collider's first scientific results with cautious optimism.

"It's a great step forward, and I think people are now allowing themselves to get excited," he said.

"If I was a nervous flyer, I would say we've taken off safely. But the trip isn't over."

The ALICE results appear online at arXiv.org and have been accepted for publication in the European Physical Journal C.

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