A Matter of Origin or the Origin of Matter?
by Connie Young
Imagine you travel back in time 15 billion years or so to witness the beginning of the universe, the so-called "big bang." You see a blinding flash, particles start flying around like crazy, and it gets really, really hot. Like any self-respecting American time-traveler, you have your camcorder in hand and are able to catch the whole thing on tape. 
Then you are zapped forward to the present, where you gather your friends and family for a screening of your one-of-a-kind home movie. But instead of showing the explosion first and the birth of the universe next, you start at the end of the tape and play it backwards - over and over and frame by frame.
This approach is similar to what particle physicists use to understand the extremely high energies that were present at the beginning of time.
"Playing the movie backward, you would see things compressing back down and condensing all the energy of the universe into a smaller and smaller region. It would get hotter and hotter, which is equivalent to further and further back in time and therefore closer and closer to the big bang," explained Robert Wilson, a high energy particle physicist at Colorado State University. 
"By recreating these conditions of the very early universe, only millionths of a second after the big bang, we hope to understand the fundamental forces of nature."
Most of the fundamental laws of physics indicate that when the universe was formed, the reaction produced equal amounts of matter and antimatter, the form of matter in which all electrical charges are reversed. A split second later, though, the antimatter disappeared, and scientists have yet to completely understand why. They have, however, discovered a few clues.
"We think there are subtle differences in the way particles decay and interact," Wilson said. "In the very early universe, if there was a very tiny amount of asymmetry, where the reaction rate for antiparticles was just a little bit higher than for matter particles, for example, then after a time, all antimatter particles would have been annihilated."
One experiment that may give them a chance to test that assertion is under way at the Stanford Linear Accelerator Center (SLAC) near San Francisco. Called BaBar, the experiment involves comparing the radioactive decay rates of two particles - the B meson and its antiparticle, the B-bar meson - to determine if this discrepancy could account for the lack of antimatter in the universe today. The task promises to be challenging, given that these particles live for only about one trillionth of a second, Wilson said. He and colleagues Walter Toki and John Harton work on BaBar and several other projects as the high energy particle physics group at Colorado State University.
The experiment has been named BaBar in part to reflect the study of the B and B-bar particles. The other reason is just a bit more whimsical. "BaBar" also is the name of a cartoon elephant popular in France, which has nothing to do with particle physics, but which does seem to prove that particle physicists have a sense of humor. "Marketers might say this wasn't such a good idea," Wilson laughed.
In the BaBar experiment, physicists shoot separate beams of electrons and positrons down a two-mile-long high energy particle accelerator. These oppositely charged particles then are stored in a large evacuated ring and are counter-rotated so they pass through each other hundreds of millions of times per second. Every thousand or so collisions, an electron in one beam gets so close to a positron in the other beam that they smash together in the middle and annihilate each other. The scientists then use particle detectors to plot the path of these collisions and observe what happened.
The data gathered from these interactions and collisions help the physicists scrutinize concepts put forth in the "Standard Model," the current theory governing the interactions of certain fundamental particles.
"With the BaBar experiment, we're investigating the special properties of the B mesons and whether there is something particular that makes them especially sensitive to the fundamental details of the Standard Model," Wilson said.
 A Presidential initiative, the accelerator project was designed to meet specifications of the BaBar collaboration, which involves some 600 physicists and engineers from the United States, France, Russia, Italy, Germany, the United Kingdom, Canada, and China. Professor Toki currently is on sabbatical at the Stanford accelerator center, where he shares responsibility for day-to-day operations of the experiment.
Another Stanford-based experiment getting assistance from the Colorado State particle physicists involves a large detector that uses very high energy to study polarized Z0 (Z-zero) particles, which are involved in radioactive decay. By studying the properties of Z0 particles, scientists may learn more about "parity violation," in which subtle, as yet unaccounted for, differences occur when experiments are run in reverse.
Colorado State's high energy particle physicists initially were recruited to work on the Super-Conducting Super Collider that was to be constructed near Dallas, Texas. A portion of this multi-billion-dollar project, had been ear-marked to support participation from other research institutions, including Colorado State. Toki was hired in 1992 to build a team to work on the super collider. Wilson came on board six months later. 
Then Congress canceled the super collider, which threatened to derail the newly established particle physics group. But Wilson and Toki found other particle physics projects to pursue and quickly got their research plans back on track, and Harton was added to the faculty in 1995.
The previous lack of a high energy physics component had been a gap at the University, Harton said. "It was like having an English department that didn't cover Shakespeare," he said.
The U.S. Department of Energy annually provides more than $400,000 in research funding for the particle physics group at Colorado State. Current research plans include the establishment of a computational facility to perform analysis of experiments performed at SLAC.
Future Linear Collider
Perhaps the most fundamental unanswered question of physics is why, in models that have been tested and proven repeatedly, there is no intrinsic accounting for the very existence of mass itself.
"We have models of how these fundamental forces work, and most are very well verified," Wilson explained. "But we have to put in the value of the mass of every single particle type by hand," Wilson commented.
One theory for this depends on the existence of the elusive "Higgs" particle, sometimes called the Holy Grail of particle physics. Colorado State physicists are helping make preliminary plans for a 20-mile-long future linear collider that would study properties of this particle.
The United States, Germany, and Japan all are pushing to have the future linear collider, which would cost billions of dollars, built in their respective countries. In August, Wilson is scheduled to begin a one-year sabbatical in Barcelona to continue his work on the project and to help coordinate American and European efforts for the future collider.
Beijing Electron Spectrometer 
This experiment is an international collaboration of American and Chinese physicists measuring charm and tau particles at a collider in Beijing. Physicists working with this experiment have made the most precise measurement of the mass of the tau lepton particle to date. Professor Toki served as the first spokesman for this project, which represents the first major Chinese scientific collaboration in high energy particle physics. 
Pierre Auger Project
Currently under construction in Argentina, the Pierre Auger Project will study rare cosmic ray showers using an array of particle detectors spanning more than 1,600 square miles. The project is named for the scientist who first observed cosmic "showers" of secondary subatomic particles created when primary high energy particles from outer space collide with air molecules.
 "It's rare, but when it happens it's very dramatic," Harton said. "The most interesting particles come at a rate of only one per square kilometer per century and have the energy equivalent to a nicely hit tennis ball. For such a tiny particle, that's an incredible amount of energy."
The United States has promised more than 
$7 million for this project. Depending on the success of the Argentina project, a Northern Hemisphere version one day may be built in Utah.
In explaining the importance of their work, Harton said particle physicists study some of the simplest, yet most fundamental, forces in nature.
"Our job is to make measurements and test theories and let the applied physicists and engineers take that fundamental knowledge and make applications," he said.
These applications may come unexpectedly.
"(When she discovered radium), Madame Curie didn't know that radiation would be a useful piece of the artillery to help cure cancer. She was just doing pure research.
"Later generations will put this information to use - I'm confident of that."