Saturday, July 7, 2001

Physicists Get a Big Bang Out of Findings Science: Tests confirm basic theory of how matter was created, but they leave a related mystery unsolved.

By K.C. COLE, Times Staff Writer

SNOWMASS, Colo.--A central piece of a major scientific puzzle fell into place Friday when physicists announced experimental results confirming a basic theory about how matter was created in the first moments after the Big Bang. The results, released by an international collaboration based at the Stanford Linear Accelerator Center, do not completely explain the mystery--indeed, as with many scientific discoveries, the new findings created even juicier mysteries. But as word of them spread like a mountain wildfire through this Rocky Mountain resort, where particle physicists were convened for an international meeting, many agreed with UC Santa Barbara's Harry Nelson, who hailed the news as "a fantastic discovery." Janet Conrad of Columbia University, who like Nelson was not involved in the experiment, echoed the sentiments: "It's a tour de force experiment. It gives all of us the sense that we're really moving forward." According to the prevailing theories about the origins of the universe, matter and its opposite counterpart, antimatter, congealed out of energy during the first moments of creation, acting according to Einstein's famous equation, E=mc2, which simply says that matter and energy are two different forms of the same basic stuff. During those first fiery microseconds, matter particles and antimatter particles froze out of energy in equal numbers; just as quickly, matter and antimatter would have annihilated each other, melting back into energy. So the critical question for physicists is, why is there any matter in the universe at all? Why didn't all the matter and antimatter simply cancel each other out? All the matter in the universe exists because nature prefers matter to antimatter by a small margin. That margin is the reason why the story of creation does not end simply with, "Let there be light." In 1967, the Russian physicist Andrei Sakharov, who later became one of his country's most famous dissidents, proposed a theory that explained the imbalance using a phenomenon called charge-parity violation. That phenomenon first had been observed in 1964 in subatomic particles called K-mesons.

Asymmetrical Surprise in Earlier Experiments Particles and antiparticles should be exact mirror images of one another, but the 1964 experiments found that K-mesons and anti-Ks transformed into other particles in a slightly asymmetrical fashion. This was a surprise to physicists, who had expected all elementary processes to be reversible, backward and forward. If their theories were correct, physicists knew, that same strange behavior would be found not only with K-mesons, but also in another, heavier, subatomic particle called the B-meson. Testing that prediction was the main reason for building a $177-million accelerator at Stanford, known as the B factory. The accelerator, which opened in June 1999, sends beams of electrons and their antimatter counterparts, called positrons, whirling around a 2.2-kilometer ring, accelerating them to near the speed of light. When an electron and positron collide, they occasionally form a B-meson and its opposite, an anti-B. Those particles exist for only trillionths of a second before decaying further. Since B-mesons disappear so quickly, the experiment had to be exquisitely sensitive. "It's very hard to build experiments that push the state of the art," said Conrad. "So it affects everyone in the community." By studying the decay patterns left by some 32 million pairs of B-mesons that were produced by the accelerator, the researchers--a team of more than 600 scientists from nine countries--found the critical asymmetries that physics theory called for. The scientists reported the result in a paper submitted Thursday for publication in Physical Review Letters, a leading scientific journal. The finding was a critical "cross-check," said Jonathan Dorfan, director of the Stanford accelerator. The observed effect is an "extremely rare phenomenon," but it will almost certainly help explain "why we live in a matter-dominated world." As a critical confirmation for a basic physical theory, the result is analogous to Sir Arthur Eddington's famous experiment early in the 20th century that confirmed Einstein's theory of relativity by measuring how gravity bent the light of distant stars. In much the same way, the Stanford findings say that physics theorists are on the right track. Eddington's experiment, in hindsight, was ambiguous, and many more tests were needed before Einstein's theory was universally accepted. In the same way, the new results, which follow previous experiments in Japan and at Fermilab, outside Chicago, will require further tests. Ironically, while the new measurement confirms the prevailing theories, it also adds to one of the biggest mysteries in science because it shows that physicists still don't entirely understand why nature prefers matter to antimatter. The difference in behavior of theB-mesons and anti-Bs accounts for only a small part of it. "There has to be some higher theory that is lying behind this," said Conrad. "This gives us a clue."

Findings Show There's Something New to Find So the measurement confirms, in effect, that there's something radically new yet to be discovered. "We know this isn't the full explanation," said Fermilab's Chris Quigg, who organized the Snowmass meeting. "We know it's a cousin [to the real explanation]," said Nelson, "but we don't know why a cousin [and] not the [explanation] itself." Even so, said Quigg, the fact that the asymmetry was found in B-mesons is "a cause for having a party." The complicated mystery of how matter came to be is a big puzzle with many pieces, Conrad said. The new finding is only one piece, "but this is the one in the middle," she added. "It's going to show us how these things fit together." * * * * * *

A Collision, a Confirmation The "B factory" at the Stanford Linear Accelerator Center accelerates electrons and their antimatter counterparts, called positrons, to nearly the speed of light. When the two collide, they occasionally produce new particles, known as B-mesons, and their opposites, the anti-Bs.

-- Anonymous, July 07, 2001