For more than 25 years, scientists at Fermi National Accelerator Laboratory in Illinois have been among the world’s leaders in seeking answers to the most basic questions of our existence in the universe: Why are we here, how did we get here, and why does the universe work the way it does?
Now Fermilab’s scientists have come up with yet another answer, and this one is among the most significant so far.
The Stuff Goose Bumps Are Made Of
At Fermilab’s Tevatron particle collider, physicists have produced the biggest discrepancy yet – one percent – between the behavior of matter particles and antimatter particles. One percent (one part in a hundred) might not sound like much, but to scientists, it’s enough of a bang to begin building a universe.
In the lab’s announcement of the discovery ("Fermilab scientists find evidence for significant matter-antimatter asymmetry," May 18, 2010), Fermilab physicist Stefan Soldner-Rembold said: “Many of us felt goose bumps when we saw the result.”
Soldner-Rembold is the co-spokesperson for the 500-member particle detector collaboration called DZero, the team that made the discovery. He added: “We knew we were seeing something beyond what we have seen before and beyond what current theories can explain.”
Any differences in behavior between matter and antimatter is called a broken symmetry, and symmetry breaking is considered the key to understanding why matter predominates in the universe.
A Light-Speed Tour Of The Particle Zoo
The four-mile underground particle collider, sometimes described as an atom smasher, is located 30 miles west of Chicago on 6,800 acres (about 10 square miles) of the Illinois prairie. Billions of collisions occur at near-light speed each second between protons and antiprotons, their antimatter counterpart. In poring over the debris of these collisions, particle physicists find all manner of particle mutations and combinations, a zone sometimes called “the particle zoo.”
In particle physics experiments at high-energy colliders like the Tevatron, collisions always produce equal amounts of matter and antimatter. But in collisions between corresponding matter-antimatter pairs (for example, an electron and an anti-electron, or positron), the particles annihilate each other and produce energy.
At CERN, the European Particle Physics Laboratory in Geneva, Switzerland the 16-mile Large Hadron Collider (public.web.cern.ch) will be running at much higher energies than the Tevatron, and thus with more discovery capabilities. The LHC has already produced collisions of seven teraelectron volts, more than three times the Tevatron energy, as reported in New Scientist ("Short, sharp science: Record LHC collisions mark new era for physics," March 30, 2010).
But in The Big Picture of the universe, there’s a problem with the balance of matter and antimatter. If the original components of the universe were equal numbers of particles and antiparticles, and if all the corresponding annihilated each other, the universe would be just a big nothing. There must be a reason for the disappearance of antimatter and the predominance of matter.
In this set of data that produced the discovery, the DZero scientists spent eight years tracking what was happening in the decay of particles called B mesons. Mesons are exotic particles formed by one quark and one antiquark – of different kinds, of course. Otherwise, a quark and its corresponding antiquark would self-annihilate.
Top And Bottom Quarks Discovered At Fermilab
Quarks are the fundamental units in all the composite particles found in the nucleus of an atom. There are six quarks in the Standard Model of Fundamental Particles and Forces, which has been the foundation of particle physics for about 40 years. Fermilab has uncovered two of them: the extremely rare top quark, uncovered at the Tevatron in 1995; and the bottom quark, discovered at a predecessor accelerator in 1977.
The protons found in the nucleus of ordinary matter are ups and downs, as detailed in the educational website The Particle Adventure ("The Fundamentals of Matter and Force," Particleadventure.org), published and maintained in detail and good humor by the Particle Data Group at Lawrence Berkeley National Laboratory in California. In this case, the B-mesons included one of the rarer quarks, the bottom – and the bottom quark is prime territory for finding symmetry-breaking decays.
And that’s just what happened in the DZero result. In tracking the meson decays, the Fermilab scientists found a one-percent discrepancy between the production of pairs of muons and pairs of antimuons. Though unfamiliar in everyday matter, the muon is a fundamental particle. Think of it as a fat electron; the muon has about 200 times the mass of the electron. Both are in the class of fundamental particles known as leptons.
Back Toward The Beginning Of Time
More and more frequently, particle physicists are creating environments that come closer and closer to the earliest times of the universe. The LHC at CERN will push the energy frontiers even closer to the earliest conditions of the universe. The ultimate goal, though still far from reach: viewing the environment of the Big Bang. That quest is explained on the LHC website: "The Large Hadron Collider: Our understanding of the Universe is about to change..."
Funding from the U.S. Department of Energy for Fermilab’s two massive collider detectors – CDF and DZero, each weighing about a million pounds – is slated to run out some time in 2011. The lab gained something of a reprieve in 2009 with $34 million in funding under the American Recovery and Reinvestment Act ("Durbin, Foster praise $48 million in funding for Fermilab, Argonne: Recovery Act funding will protect jobs and support research at Illinois labs," joint press release by Sen. Richard Durbin and Rep. Bill Foster, March 23, 2009). The clock is still clicking on the Tevatron, but the venerable discovery machine seems determined to go out with flags flying.
Mike Perricone - For nearly a decade, I served as Senior Editor and science writer in the Office of Public Affairs at Fermi National Accelerator Laboratory ...
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