Particle Man- page 2 | Space | Air & Space Magazine

Particle Man

Sam Ting is on a mission: find the other half of the universe.

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(Continued from page 1)

Scientists have also seen anti-hydrogen in nature. Mimicking what happens in accelerators, cosmic ray particles crashing into particles in the atmosphere produce a secondary shower of anti-protons and positrons. But high-altitude balloons have yet to detect anti-atoms of heavier elements—which could only be forged inside distant anti-matter stars by nuclear fusion, just as ordinary carbon, iron, and other elements are created in the furnaces of ordinary stars. In other words, we see no evidence of anti-stars and anti-galaxies wheeling in the sky. And that presents astrophysicists, who like symmetry, with an embarrassing question: If the birth of the universe created matter and anti-matter in equal parts, as Dirac’s equations demand, where’s the other half?

The best explanation offered to date is that our universe is all that remains of the mutual annihilation of matter and anti-matter that took place shortly after the Big Bang. The two materials duked it out until only a small amount of matter—what we today call the universe—was left standing. That means matter was granted some slight advantage. Scientists call this puzzlement the charge parity violation—“CP violation” for short.

High-energy physicists are busy investigating the theory in accelerators, while astrophysicists look for signs of anti-matter stars and galaxies. Until one or the other succeeds, says Steve Ahlen, a Boston University physicist involved in the early stages of the AMS project, the jury is still out: “No one really can demonstrate how the universe could have no anti-matter,” he says.

Enter an experimentalist like Ting, who has little patience with theorizing. “If you listen to the theorists, you would do nothing,” he says. So when the anti-matter question caught his attention in 1994, Ting ignored the warnings of colleagues and starting working on ideas that could turn up primordial anti-matter.

Though his is the most ambitious, it is not the first. As far back as the 1970s, fellow Nobelist Luis Alvarez was on the trail. More recently, two high-altitude instruments—the Balloon-borne Experiment with a Superconducting Solenoidal magnet (BESS), run by NASA and Japanese researchers, and the High-Energy Anti-matter Telescope (HEAT), sponsored by a consortium of universities, have counted about 1,000 anti-protons to date, the results of cosmic ray collisions in the atmosphere. But still no sign of heavier anti-atoms forged inside anti-stars. The CP theorists doubt they are there to be discovered, and even some experimentalists have grave reservations about finding them.

One reason is distance. No significant amount of anti-matter is believed to exist in our own supercluster of galaxies, or within about 30 million light-years of Earth. If it did, we would see enormous flashes of gamma rays from the mutual destruction of matter and anti-matter—and we don’t. Any anti-atoms created in anti-galaxies must have originated near the edge of the visible universe. In theory, those anti-particles could have crossed that vast distance to reach Earth, but most would have been trapped by the magnetic fields surrounding stars and galaxies along the way. “Even if anti-stars and anti-galaxies exist, they are so far away it would be quite hard for particles to come close enough for observation,” laments Dietrich Müller, a University of Chicago physicist and spokesperson for the HEAT project.

Yet Ting has made a career of proving the common wisdom wrong. His proposal in the early 1970s to search for a new kind of particle that decays into pairs of electrons and positrons was turned down by several accelerator committees; he was finally given a shot at the Brookhaven National Laboratory on Long Island. By 1974, after 18 months of experiments, he had found what he was looking for. Nearly simultaneously, Burton Richter of Stanford found the same thing, and they shared the Nobel Prize for discovering the “J-psi” particle two years later.

Ting was only 40. It was an astonishing achievement for a Chinese immigrant who had arrived in Ann Arbor, Michigan, two decades earlier with only rudimentary English and $100 in his pocket. He quickly earned scholarships that led to a physics doctorate in 1962. “He was a young man in a hurry,” recalls Lawrence Jones, who had co-chaired Ting’s thesis committee and is now an emeritus professor at the University of Michigan. Ting joined the MIT faculty in 1969, and his interest in particle physics took him frequently to CERN in Geneva. There he came to lead one of the costliest basic research projects in history: the L3 Experiment, which involved nearly 500 physicists from 40 institutions and cost $200 million for equipment alone.

By 1994, the peripatetic Ting was in search of a new challenge. The collider used for his experiment was due to be shut down to make way for a larger machine, so his work at CERN to discover yet more microparticles was soon to end. The U.S. Congress and the new Clinton administration had killed the massive Superconducting Super Collider the year before. And Ting’s proposal for a massive experiment using CERN’s next big accelerator, the Large Hadron Collider, had been rejected.

That left few options in the traditional field of high-energy physics. So in early 1994, Ting called together a small band of colleagues. It was one of those rare moments when researchers have a chance to be wildly creative. “For a couple of months we sat around and gave any good idea a hearing—as well as a lot of bad ideas,” recalls Peter Fisher, an MIT collaborator. “It was an extraordinary time, sitting around with all these great minds.” Boston University’s Ahlen pushed for building a massive collector deep in a Tibetan canyon to search for gamma rays from space, while others proposed spacecraft that would carry sophisticated particle detectors.

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