May 19, 2010

Physicists On Track To Understanding Vastness Of Matter

Physicists at Fermilab have discovered a clue as to why the world around us is composed of normal matter and not anti-matter.

Today, anti-matter is rare, but it can be produced by atom smashers, in nuclear reactions, or by cosmic rays.

However, physicists believe the Big Bang should have produced equal amounts of matter and its opposite.

The DZero experiment at Fermilab in Illinois has now produced results that provide a clue as to what happened to all the anti-matter.

Many researchers regard this as one of the biggest mysteries in cosmology.

The data from the experiment offers hints of new physics beyond what can be explained by current theories.

For each basic particle of matter, there exists an anti-particle with the same mass but the opposite electric charge.

For example, the negatively charged electron has a positively charged anti-particle called the positron.

However, if a particle and its anti-particle collide, they are "annihilated" in a flash of energy, yielding new particles and anti-particles.

If a similar process occurred at the beginning of the Universe then it would have left us with equal amounts of matter and anti-matter.

However, today we live in a universe made up overwhelmingly of matter.

Researchers working on the DZero experiment observed collisions of protons and anti-protons in Fermilab's Tevatron particle accelerator.

They discovered that these collisions produced pairs of matter particles more often than they yielded anti-matter particles.

There is a 1 percent difference in the production of pairs of muon (matter) particles and pairs of anti-muon (anti-matter) particles during these collisions.

"Many of us felt goose bumps when we saw the result," Stefan Soldner-Rembold, one of the spokespeople for DZero, told BBC News.

"We knew we were seeing something beyond what we have seen before and beyond what current theories can explain."

The overwhelming numbers of matter in the Universe are only possible if there are differences in the behavior of particles and anti-particles.

Physicists had already seen these differences, but they were too small to explain why the Universe appears to prefer matter over anti-matter.

Previously, these observations were fully consistent with the current theory known as the Standard Model.  This theory explains the interactions of sub-atomic particles.

Researchers wrote in the journal Physical Review D that the new findings show much more significant "asymmetry" of matter and anti-matter.

If the results are confirmed by other experiments, then the effect seen by the DZero team could move researchers along in their efforts to try and understand the dominance of matter in today's Universe.

The data presage results expected from another experiment, called LHCb.

LHCb, which is based at the Large Hadron Collider near Geneva, was specifically designed to shed light on this question in particle physics.

Dr. Tara Shears, a particle physicist at the University of Liverpool who works on LHCb and CDF, told BBC "It's not yet at the stage of a discovery or an explanation, but it is a very tantalizing hint of what might be."

Shears, who is not a member of the DZero team, added: "It certainly means that LHCb will be eager to look for the same effect, to confirm whether it exists and if it does, to make a more precise measurement."


Image Caption: DZero Detector with large liquid argon calorimeter.


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