All that matters

Cox.
Photo by Jack Mellott.

U.Va. professor Brad Cox approaches mysteries much as a detective tackles a difficult case. Skillfully and patiently, he collaborates with a team to amass evidence, analyze it for clues and deduce an answer. But rather than solving crimes, Cox and his team unravel puzzles in the field of high-energy physics. For anyone who struggled through trigonometry class, their work may seem hopelessly esoteric. Actually, though, it touches our lives in very tangible ways. By unlocking the secrets surrounding the universe, Cox and others in the U.Va. Physics Group edge us ever closer to understanding our origins as human beings.

The group includes Cox and eight other professors, post-docs and graduate students. In 2004 they concluded a 10-year, groundbreaking experiment known as KTeV, short for “kaons at Tevatron.” Funded by the U.S. Department of Energy, the National Science Foundation and a host of international agencies, the KTeV experiment sought answers to the differences between matter and antimatter. Today the universe teems with matter, from our bodies and every other tangible thing here on Earth to the stars and planets twinkling in the night sky. Matter is, quite simply, all that matters. Yet, physicists believe, this was not always the case.

Thirteen billion years ago, the Big Bang spawned equal amounts of matter and antimatter, but in a cataclysmic showdown, matter annihilated antimatter. If the two were still present in equal amounts, Cox explains, the “universe would [likely] be a wilderness with matter continuously annihilated by antimatter.” Matter must have some edge on its counterpart. Otherwise, Cox notes, “we as humans wouldn’t be here.”

To understand why antimatter disappeared, the U.Va. team re-created the Big Bang’s immediate aftermath at the Fermi National Accelerator Laboratory -- or Fermilab, for short -- a high-tech facility owned by a consortium of research universities. During the KTeV experiment, Fermilab became the researchers’ home away from home as they repeatedly trekked from Charlottesville to this facility located 40 miles west of Chicago.

Using Fermilab’s Tevatron, the world’s highest-energy particle accelerator, the U.Va. team simulated the conditions following the Big Bang. Tevatron’s capacity is astounding: Fermilab accelerator scientists send beams of tiny matter particles rocketing around Tevatron’s four-mile course before reaching an energy level of almost one trillion volts and being directed to the experiment. As the particles hit a target and break down, the KTeV team forms a beam of kaons, sub-atomic particles known for their nonconformity. Unlike other particles of matter that follow the rules of physics, the wayward kaon sheds light on why matter, not antimatter, abounds in our universe.

For the final phase of the KTeV experiment, the U.Va. group worked to solve a long-standing mystery surrounding the kaon’s decay rates. If the decay probabilities of the neutral kaon are added with those of other decays, the total should add to one. For years, though, the totals were off, indicating that some measurements must be wrong or that an unknown factor held sway. The U.Va. group began the daunting task of redoing measurements going back 45 years. Since cuts in federal funding made future experiments in this area unlikely, the group felt added pressure. “We knew this would be the ultimate experiment,” Cox says. “Whatever we found would probably stand for all time in certain areas.”

After gathering nearly 1,000 times more data than used in previous experiments, the team found that incorrect measurements were indeed the culprit. The new data showed that the probabilities do add up to one. Within the particle physics community, this result made big news, and this past February, a panel of 10 physicists unanimously named this result the best Fermilab measurement of 2004.
 
Regarding the benefits of the KTeV experiment, Cox says, “It’s hard to know exactly how it will affect us. But when I look back on the history of physics experiments, it’s mind-boggling how much they have influenced the way we live now in the 21st century.” From new cancer treatments to magnetic resonance imaging and computer technologies including the internet, previous research has undoubtedly bettered our lives. For Cox and the U.Va. Physics Group, the universe’s unsolved mysteries hold tremendous promise.