Come-From-Behind Success

On the 25th anniversary of the b-quark discovery, Fermilab scientists recall overcoming a slow start

by Kurt Riesselmann

Research can be as dramatic as a sports tournament. Even if you are off to a slow start, your team still can show a strong performance in the playoffs.

The discovery of the bottom quark, found twenty-five years ago at Fermilab, is a case in point.

In the seventies, collaborators of the Fermilab experiments E70 and E288 were at the center of a drama that unfolded over a seven-year period. It included such exciting times as the “November revolution” in 1974, when experimental groups at Stanford and Brookhaven simultaneously reported the discovery of a fourth type of quark, the charm.

By any luck, and with better timing, that discovery could have been made at Fermilab.

“Fermilab unfortunately was just one step behind,” said John Yoh, who joined Fermilab in the early seventies. “We had a new machine, and there were several experiments that—if they had been further along—could have discovered the J/Psi,” the particle composed of a charm quark and anti-quark.

The J/ Psi announcement came only nine months after scientists from Columbia University and Fermilab decided to upgrade their experimental apparatus known as E70 and proposed in a one-page letter to director Robert Wilson that with the follow-up experiment, called E288, they would search for particles like the W boson to “publish these and become famous.” Their colleagues in California and on Long Island, however, were the first to stand in the limelight.

“After the November revolution we at E70 realized that we had missed the boat,” Yoh recalled.

But the experimenters at Fermilab were far from throwing in the towel. They knew that Fermilab’s new Main Ring accelerator would eventually be fifteen times more powerful than Brookhaven’s AGS ring, presenting a huge window of opportunity to produce new, heavier particles.

“There was a huge mass region, totally unexplored,” recalled Leon Lederman, the spokesperson of E70 and E288. “We were on a hunt for vector mesons and anything new would have been welcome.”

By the spring of 1977, E288 experimenters had made another upgrade to their experiment, collecting one thousand times more data than in 1975. Fermilab’s first major discovery was just around the corner.

“After a few weeks with the new configuration, we found that the probability to produce muonantimuon pairs peaked sharply at about ten times the proton mass,” said Dan Kaplan, who worked on E288 as a graduate student and is now a physics professor at the Illinois Institute of Technology. “We were observing a new quark.”

The new result from Fermilab, soon identified as the bottom quark, had a big impact.

“The discovery of the charm quark convinced people that quarks are more than a mathematical construct,” said Jeff Appel, who moved from New York to Batavia to lead the E70 team as Lederman’s deputy. “The subsequent discovery of the bottom quark convinced people immediately that there must be a third generation. There were expectations that another quark—probably three times heavier than the bottom quark—should exist.”

Nature, however, made it more difficult for the ‘quark detectives’ to find the missing piece. It took another eighteen years until scientists discovered the bottom’s partner—the top quark, which was twenty-five times heavier than the bottom quark. Scientists had to wait for construction of Fermilab’s Tevatron accelerator, completed in 1986, to create collisions powerful enough to produce top quarks. Why the tiny particles—first seen in 1994—are as heavy as a gold atom is still one of the big mysteries of the subatomic world.

Today, bottom quark physics is more important than anyone could have imagined.

It took about 20 physicists and technicians, from Columbia University, Fermilab and the State University of New York at Stony Brook, to find the bottom quark. Left to right: Dave Hom (formerly Columbia University), Chuck Brown (FNAL), Al Ito (SUNY, now FNAL), Bob Kephart (SUNY, now FNAL), Koiji Ueno (FNAL), Ken Gray (FNAL, now retired), Hans Sens (Columbia University, now ILNL, France), Steve Herb (Columbia University, now DESY, Germany), Jeff Appel (FNAL), Dan Kaplan (SUNY, now IIT). Collaboration members not shown in these photos: David Snyder (Columbia University, now Gallaudet University), Taiji Yamanouchi (FNAL), Hans Jöstlein (SUNY, now FNAL), William Sippach (formerly FNAL) and people from the Fermilab accelerator division.

“This Fermilab discovery has generated a huge activity: two large new accelerators adding to the Tevatron, which has been a workhorse of the subject,” said Lederman, who shared the 1988 Nobel Prize for a neutrino experiment he carried out at Brookhaven in 1962. “New major detectors at Fermilab, DESY and CERN... I would think the attention is flattering, matched only by neutrino physics as the two HEP activities that stand outside of pushing the frontiers of energy.”

Particles containing bottom quarks are the perfect instrument to learn more about a tiny flaw in the mirror-like behavior of matter and antimatter. The imperfect symmetry, referred to as CP violation, may be the key for why the universe has matter— including the stuff we are made of.

“Yesterday’s discovery is today’s tool,” said Appel. “Scientists have built B factories in California and Japan to study this. And our Fermilab experiments, CDF and DZero, should provide excellent answers, too.”

Play by play, particle physics continues its success story around the world.