For Physicists: There Is Light After the End of the Tunnel
WITH the demise of the Superconducting Super Collider (SSC), particle-accelerator physicists lost an opportunity to probe the intriguing question of why matter has mass. Now they are challenged to answer the equally intriguing question of why there is any matter at all.
While the political fight over the $11 billion Texas-based super collider diverted public attention, the United States Department of Energy quietly approved construction of a much-less-costly $177 million particle collider in Stanford, Calif. It will be uniquely adapted to study a subtle phenomenon that may explain why there's any matter left today to make galaxies and planets. The question arises because cosmological theory implies that any matter created in the first split second of the universe's existence should have quickly transformed into radiant energy.
The new machine ``won't replace the SSC,'' says physicist Michael Riordan at the Energy Department's Stanford Linear Accelerator Center (SLAC), which will build and run it. But, he adds, ``This is a remarkably cost-effective facility, [and] it's exciting physics.''
This is the perspective from which American physicists are beginning to see the SSC loss. Initial dismay is giving way to the realization that there still is ``exciting physics'' to be done. American physics ``is not a wasteland,'' says Cornell University physicist Karl Berkelman. Focus on low-energy physics
Dr. Berkelman, who also bid for the new facility, explains that some basic physics problems can only be tackled at ``the high-energy frontier'' because they involve particles that have not yet been detected. That is where the SSC would have come in. There are other puzzles that can best be studied with lower energy but more intense particle beams. ``That's where we are now,'' he says.
In all this kind of research, physicists are dealing with the almost magical properties of the two basic forms or matter - ordinary particles and their antimatter twins. Antimatter is just like ordinary matter except that certain properties, such as electric charge, are reversed. When particles of matter meet their antimatter twins, they mutually annihilate each other. They transform themselves into pure radiation, notably gamma rays. Conversely, radiant energy can congeal into matter. But it always does this in matter-antimatter pairs of particles.
Colliders rely on this two-way process. The SSC would have smashed together beams of protons and antiprotons, each with the unprecedented energy of 20 trillion electron volts. An electron volt is the energy an electron gains when accelerated by a voltage difference of one volt. It would take the SSC energy to produce the phenomena that physicists think could explain how particles acquire their mass. But physicists don't need that much energy to study why matter exists. They can do it at energies around 10 billion electron volts, which the new SLAC facility will provide.
It will adapt an existing collider to smash together beams of electrons and positrons, the electron's antiparticle. As colliding electrons and positrons transform into pure energy and recongeal into other forms of matter, physicists will be looking for a particular particle called the B meson and its antiparticle. This may hold the key to matter's existence.
According to current theory, the early universe had equal amounts of matter and antimatter, which should have annihilated each other to once again become radiation. Something tipped the balance in favor of the ordinary matter we know today. Slower rate of decay a key
The B meson suggests what that ``something'' may be. It breaks certain rules that generally govern particle behavior. This shows up as a slower rate of decay for ordinary B mesons as opposed to antimatter B mesons. This kind of difference in rates of decay may have favored ordinary matter in the early universe.
Physicists need lots of B mesons to study this. That is what the new Stanford facility is designed to produce - hence the name B-factory. Cornell will develop a smaller B-factory with National Science Foundation funding. With plenty of B mesons to study, the question of how matter escaped total annihilation will be ``quite addressable,'' the SLAC's Dr. Riordan says.