Scientists Ponder Universe's Missing Antimatter

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The head-scratching problem for particle physicists is, if equal amounts of matter and antimatter were created at the big bang, why is there only matter left around? Why didn't all the matter and antimatter meet up and annihilate, leaving a universe without matter?

According to Drell, shortly after the big bang, most of the matter and antimatter did annihilate, but one in a billion particles survived "and that became the galaxies, the universe, and us as we know it now," she said.

But why? How?

CP Violation

The answer lies at least partially in an effect called charge parity (CP) violation that indicates matter and antimatter decay differently, Drell said.

In experiments conducted at the B factory particle collider at SLAC, Drell and colleagues were able to partially determine the differences in decay between elementary particles and antiparticles.

But the degree of CP violation determined by this experiment—and others—fails to account for the entire matter-antimatter imbalance in the universe.

"We don't have a complete understanding yet. Our current picture and understanding doesn't give enough CP violation," Drell said.

The hope is that ever more sophisticated instruments at the Large Hadron Collider and the International Linear Collider will allow particle physicists to look for other processes and effects that account for the asymmetry between matter and antimatter.

The Large Hadron Collider is scheduled to be turned on in 2007. It will accelerate protons around two 16.7-mile (27-kilometer) rings to near the speed of light and smash them together.

The International Linear Collider is still in the proposal stage. It would create high-energy particle collisions between electrons and positrons. Positrons are the antimatter counterpart to electrons.

The resulting explosions at the colliders will tear the particles apart, allowing scientists to study what makes up the matter and answer questions about the structure of the universe, including what happened to all the antimatter.

Harms of the Fermi National Accelerator Laboratory equated these next-generation particle colliders to "supermicroscopes," allowing scientists to study the collisions with finer resolution.

"They'll allow us to achieve higher energy than what we have now to probe further into the structure of matter," he said.

Currently, the Tevatron collider at Fermilab is the most powerful particle accelerator in the world. It brings protons and antiprotons together in a 4-mile (6.4-kilometer) long underground ring.

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