Jefferson Lab’s Hall A experiment examines how energy becomes matter

Just as matter can be converted into energy, so too can energy become matter. That’s what five-dozen Jefferson Lab researchers were counting on for an experiment in Hall A

Albert Einstein figured it out by 1905, as he was formulating his special theory of relativity: while you can’t exactly get something from nothing, you can come close. His famous formula, E=MC², works both ways. Just as matter can be converted into energy, so too can energy become matter.

That’s just what five dozen researchers were counting on with a Jefferson Lab experiment in Hall A that used the Lab’s electron beam and a liquid hydrogen target to bring to life an unusual particle known as a kaon. The kaon’s unique structure could prove of great help to cosmologists, who should be able to use the results of experiments like the Hall A effort to develop structural models of stellar objects made up of exotic, or “strange” matter, matter that includes kaons as part of their own subatomic architectures. Preliminary findings indicate that kaon production results from the interactions of the particles of light known as photons. The photons create more than just kaons, however. They also produce other particles, known as lambda and sigma, with their own distinctive quark structure. All arise from a constantly churning sea of “virtual” particles that can’t exist until bumped by a jolt of energy such as that provided by the Lab’s accelerator.

“When these things get produced, we’re trying to understand how they’re made,” says experiment co-spokesperson Pete Markowitz, associate professor of physics at Florida International University in Miami. “And: what do they look like? We’re trying to come up with a detailed picture of how quarks ’live’ in the nucleus.”

The first challenge confronting the Hall A researchers in their experimental run that concluded this past March was to actually make enough of the rare, fleeting particles. The task was a difficult one, considering that kaons contain a matter-antimatter pair of an “anti-strange” quark and one “up” quark (quarks are thought by many scientists to be the basic building blocks of matter). Should a particle of antimatter collide with one of normal matter, both particles are instantly converted to energy, a process that doesn’t lend itself to easy observation.

The Hall A scientists succeeded in making enough kaons for long enough to be able to probe the particle’s internal details. In essence, the researchers “paid” for the kaon-constituent quarks to come into existence by using the electron beam’s energy. “We created a kaon essentially out of nothing by giving it a jolt of energy,” Markowitz says. “Then our job was to measure the properties of that creation. We wanted to determine which parts of the kaon are quark-like. We’d like to identify exactly how kaons get made. What description, theoretically speaking, is the most appropriate?”

Planning for the first kaon experiment began in 1993 when Markowitz first conceived the idea. A follow-on investigation that will study another strange-matter particle, known as a hyperon, is scheduled for 2004 and will involve a team of up to 80 researchers, most of whom worked on the kaon experiment.

“[The hyperon study] will be the first time in history that people will be able to see what’s going on, and at high resolution,” Markowitz says. “We’ll be creating a new form of matter. I’m really excited about this experiment.”

by James Schultz