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Discovery of the smallest particle could lead to Nobel Prize

Updated: December 10, 2009 - 3:44 pm

Posted: July 21, 2003

Scientists at the Thomas Jefferson National Accelerator Facility have found compelling evidence that a previously unknown type of subatomic particle exists. The discovery of the so-called "pentaquark," which has received international attention and could one day merit the awarding of a Nobel Prize, illustrates the high level of cutting-edge research taking place at the Newport News lab's Continuous Electron Beam Accelerator Facility (CEBAF).Many area residents are unaware that Hampton Roads is home to the premier center for quark research in the world. Most of those who do know there is a particle accelerator in Newport News recognize the name Jefferson Lab only from the fleeting sign they drive by on Interstate 64.Quarks make up the protons and neutrons of atoms and are the smallest particles physicists have observed in experiments. The newly discovered pentaquark, which is technically known as "theta-plus," is formed when five quarks bond into one particle. Previously, quarks had been observed only in groupings of twos or threes.In other words, the pentaquark is "a new form of matter," said Elton Smith, a member of the CEBAF Large Acceptance Spectrometer collaboration, a multinational group of researchers working at Jefferson Lab, and one of the lead authors of the paper reporting the findings. The discovery will not result in immediate practical applications. Rather, it furthers scientists' understanding of the fundamental elements of nature.The story of the discovery of the pentaquark starts in Russia, where in the late 1990s Dmitri Diakonov, a theoretician at the Petersburg Nuclear Physics Institute, postulated an experiment that he believed would show the existence of the pentaquark. Over lunch during a February 2000 conference in Adelaide, Australia, Diakonov explained his theory to Smith, from Jefferson Lab, and Takashi Nakano, an experimental physicist from Japan. Smith and Nakano then returned to their respective particle accelerators armed with the knowledge of how to look for pentaquarks. Three years later, teams of scientists from both Japan's SPring-8 facility and Jefferson Lab, as well as another group at the Institute for Theoretical and Experimental Physics in Moscow, have independently found data confirming the existence of pentaquarks.The Japanese announced their findings first, at a 2002 conference in Osaka, Japan. However, the Jefferson Lab data, which was released at a New York City conference this May, not only confirms the original results but is considered more reliable. The Japanese team agrees that the Virginia data is better because the Jefferson Lab accelerator is more powerful.Most of the credit for finding the pentaquark likely will go to Diakonov and possibly Ohio University's Ken Hicks, who works on both the American and Japanese teams. Stepan Stepanyan, who works for Jefferson Lab, was the lead author of the local group's findings. One of the most fascinating aspects of the pentaquark experiment, and of Jefferson Lab's work in general, is what actually happens inside the particle accelerator.It shoots electrons. The Jefferson Lab accelerator is shaped like a track and almost a mile long. Electrons orbit the track up to five times at nearly the speed of light, acquiring more and more energy the farther they go. At the end of its journey, the electron slams into a target, such as an atom of hydrogen, carbon, gold or lead. The impact breaks the atom apart, enabling physicists to study the building blocks of matter.The tunnel housing the accelerator is built 25 feet below ground, to ensure safety in case one of the high-energy particles misfires. The electrons travel around the 7/8-mile circuit five times in 20 millionths of a second. At that pace, the electron would encircle the earth 7.5 times in one second.Because CEBAF is the most powerful superconducting electron accelerator in the world it is the best available for the study of quarks. Scientists specializing in quarks therefore travel to Newport News from around the world to conduct their research. The summertime is especially busy, when additional students and researchers join 550 full- time employees and 350 contractors. On any given summer day, as many as 1,500 people are working at the research complex, according to the lab's spokeswoman, Linda Ware.The reason the Jefferson Lab accelerator is so powerful is because it shoots electrons through state-of-the-art cryomodules (the tube) containing super-cooled niobium cavities (the little tube within the main tube). These components use advanced superconducting radio frequency accelerating technology to effectively reduce the amount of friction counteracting the speeding electrons, enabling relatively low-cost, high-efficiency operation. Or, in layman's terms, the accelerator has well-greased skids. In fact, Jefferson Lab makes such quality components that it has been awarded a $75 billion contract to build 81 niobium cavities for 23 cyromodules for a new accelerator in Oak Ridge, Tenn.Because the discovery of the pentaquark is one of the more important finds in the history of Jefferson Lab, it will bring more research dollars to the facility, said Fred Dylla, who is in charge of applied science at the lab. The amount of publicity the pentaquark story has received in journals like Science, Nature, The New York Times and The Los Angeles Times shows the importance of the discovery."The sheer fact that [the discovery] was picked up and sent to all these prestigious publications very quickly indicates its value," Dylla said.According to Terry Riley, executive director of the Hampton Roads Technology Council, such high-profile science helps boost the overall business climate in the Hampton Roads technology sector."What happens when you have world-class particle physicists in your neighborhood? It has to do with intellectual density," Riley said. "People want to be where that sort of thing is going on."Instead of a product synergy, Riley said that "it's more like an intellectual synergy and that does lead directly to product innovation."Whether or not the pentaquark breakthrough will win a Nobel Prize — the crowning achievement in the physics world — remains to be seen."Discoveries of new types of particles have often been awarded the Nobel Prize," said Smith. "Whether this would be considered a new particle would be a decision the Nobel committee would have to make."