UA Physicists Help Discover Clue to Antimatter Conundrum

If the new finding is confirmed, it suggests the existence of types of particles that physicists have never before observed.
May 20, 2010
The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. (Photo courtesy of Fermilab)
The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. (Photo courtesy of Fermilab)
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A new asymmetry between matter and antimatter may help explain why antimatter is so rare, according to new research. The finding may also shake up physicists' current explanation about the interactions among the particles that make up matter.

Three physicists from the University of Arizona contributed to the new finding from the DZero experiment, which was announced by Department of Energy's Fermi National Accelerator Laboratory

"We have an equal amount of matter and antimatter coming into our experiment. Now we see one percent more matter muons than antimatter muons coming out," said Varnes, a UA associate professor of physics and DZero team member.

"We didn't expect this. The current theory didn't predict this," said Erich Varnes, who has a leadership role in the 500-member DZero collaboration. "If this is confirmed, this is physics beyond the Standard Model."

The Standard Model is the underpinning for much of our understanding about matter and the nature of the universe.

The DZero experiment measures the particles and energy given off when beams of protons and antiprotons smash together inside the Fermilab's Tevatron, a four-mile circular tunnel located in Batavia, Ill. Muons are one of the particles that result from the collisions.

The new result has now been posted on the Internet and submitted for publication in Physical Review D. All members of the DZero collaboration are co-authors on the paper, including Varnes, UA physics professor Kenneth Johns, and UA physics research associate Amitabha Das.

There is still more work do, Varnes said.

"We don't have enough data that we're statistically sure yet," he said. "Imagine your team is in the Superbowl, and they're up by 14 points in the third quarter. That's a very exciting position to be in – but they haven't won the game yet."

The new finding, if confirmed by further testing, will require that physicists make some adjustments in the Standard Model, he said.

"You have to play the rest of the game. We have to keep collecting data at least until the end of 2011," he said.

Varnes does not anticipate being able to confirm the tantalizing new finding until 2012.

If the new finding is confirmed, it suggests the existence of types of particles that physicists have never observed before, he said. The Large Hadron Collider, the world's biggest particle collider, may be powerful enough to produce those particles.

Varnes and four other faculty members in UA's physics department are part of the team working on the LHC's ATLAS experiment.

The U.S. Department of Energy, the National Science Foundation, and a number of international funding agencies fund the Tevatron's DZero experiment. DZero is an international experiment conducted by 500 physicists from 86 institutions in 19 countries.

While Varnes was not directly involved in analyzing the data for this new finding, his work is critical to all the DZero results. As co-leader for algorithms and computing, he ensures that the computing tools – both the hardware and the software – are up to the task of analyzing the massive amounts of data generated by the experiments.

Johns led the design and construction of the Level1 muon trigger electronics being used in the DZero experiment. The new finding is based entirely on detecting muons and would not have been possible without the trigger system that Johns designed, Varnes said.

Both the LHC and the Tevatron are designed to slam subatomic particles together at nearly the speed of light and then observe what kinds of energy and particles spew from the collision. Fermilab's Tevatron smashes protons and anti-protons together, whereas the collisions within the LHC are between two protons.

The LHC, 17 miles in circumference, is located under the Franco-Swiss border.

The energy of collisions at the LHC will be seven times higher than those at the Tevatron because the LHC is much larger and also because it uses more powerful magnets to bend the beams of protons around their circular path. The LHC will also have more collisions, increasing the likelihood of observing new phenomena.