On the Trail Of That Elusive Top Quark
IN the quest for scientific knowledge, one person's discovery is another person's challenge. A discovery isn't a discovery until independent research confirms it.
So it is with the top quark - the long-sought missing member of the elementary material particle family. Reports of its ``discovery'' made headlines last month.
The multinational discovery team, however, was cautious in its announcement. Working at the Fermi National Accelerator Laboratory at Batavia, Ill., it only claimed ``good evidence'' and ``not proof positive'' that the top quark actually exists, as team co-leader Tony Liss of the University of Illinois at Urbana-Champaign put it.
The elusive particle remains elusive - an example of the often tantalizing nature of this kind of research. But another search team working at Fermilab is hot on its trail.
Team member Richard Partridge of Brown University at Providence, R.I., explains: ``We're not able to confirm [the particle] at this time.... In scientific circles, that's crucial.... Many things have been claimed and not all of them confirmed.'' Working at a location on the accelerator known simply as D-zero, Dr. Partridge's team hopes to supply that crucial confirmation. The other team, working at a different location, is known as the Collider Detector collaboration.
D-zero's experimental run began last December and lasts through July 1995. Computers will sift through something like a trillion particle interactions to find the telltale events. As protons and their antimatter counterparts smash together in the accelerator, they release energy that transforms into a myriad of other particles. Only 1 such event in 100,000 is ``significant'' enough to claim the experimenters' attention. Even then, many uninteresting phenomena mimic the top-quark signature.
That quark is elusive because it's heavy. Although far smaller than an atom, it's as massive as a rhenium atom and nearly as massive as gold. It takes a lot of energy to make a particle that heavy - about ten percent of the total energy the accelerator collisions provide. Given the many ways a proton-antiproton collision can spend its energy, top-quark creation doesn't happen very often.
Physicists want to prove that this does happen in order to round out the evidence for their current theory of matter's basic structure. It's an incomplete theory. It neglects gravity and can't explain why matter has mass. But it's the best theory they have. It includes a set of six particles called quarks that are whimsically named up, down, strange, charmed, bottom, and top. The up and down quarks make up most matter. Physicists have found all the quarks except the top.
If the D-zero group sees the top quark at all, Partridge expects it will provide significant confirmation of the earlier tentative sightings. If it sees nothing, physicists will have to wait several years until a planned upgrade of the accelerator improves their chances of success.
There will be no ``eureka'' moment of startling discovery. Just a slow buildup of evidence. An anonymous poem that appeared on the Internet information highway says it all:
And so there you have it.
The TOP's in the bag.
And so on, researchers
can rightfully brag.
But wait! It's still out there!
Could it really be true!
And who'll really find it?