U of R physicists helping lay the groundwork for understanding the nature of nuclear matter
Everyone knows how to take a traditional photograph – load the film into a camera, snap the shot, and then develop the film. But how do you take a picture of a subatomic particle whose lifespan is only 26 billionths of a second? Your camera would have to have a powerful lens and a really fast shutter speed.

University of Regina physics professor Dr. Garth Huber is part of a team that has taken such a picture using the only “camera” in the world capable of doing this type of work – the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. Their work, recently published in the prestigious international physics journal Physical Review Letters, is helping others understand the nature of the visible universe.

So why would you study a subatomic particle which is so small and short-lived?

“In general terms, the aim of my research is to better understand the fundamental structure of nuclear matter,” Huber explains. “Everything in the universe is made up of atoms, and each atom in turn contains subatomic particles called hadrons which are basically the building-blocks of matter. The type of hadrons I study – particles called pions – are incredibly important in the Yukawa model of nuclear physics because they are responsible for holding the nucleus of the atom together and thus giving form to everything around us.”

The pion’s function is relatively straightforward: the constant exchange of pions between protons and neutrons is a major component of the nuclear strong force which binds the nucleus together and helps give the atom its form. But pion structure itself has not yet been completely defined – something that isn’t surprising given the particle’s small size and incredibly short lifespan.

To help define this structure, in 2001 Huber and a group of 52 other scientists from more than a dozen institutions designed an experiment to basically take a “snapshot” of a pion. The experiment was conducted in 2003 at the Jefferson Lab, where electrons were sent into a liquid hydrogen target and interacted with a cloud of virtual pions surrounding the hydrogen nucleus. The escaping charged pions and scattered electrons were then detected at precisely the same instant.

Since that time, Huber and his colleagues have been analyzing the data – developing the film, if you will – to construct what amounts to a “numerical snapshot” of the pion at the instant of scattering. To say the project is finished would be inaccurate, however – others will now use this picture to help refine theories on the structure of matter.

“We are a long way from an all-encompassing understanding of the universe, but by better-defining the structure of the pion, we can get a better understanding of the strong nuclear force responsible for nearly all of the visible matter around us. This might not have a practical application for most people, but for theorists trying to determine how matter is formed and continues to exist, it will be important.” Huber notes. “The pion is usually pictured as a relatively simple system consisting of one quark and one anti-quark, and has special importance because it is the lightest known quark/anti-quark state. With the published data from our experiment, however, theorists will have the opportunity to develop a clearer idea of the pion’s structure. ”

Interestingly, one of these theorists who will be studying Huber and his team’s pion snapshot is also from the U of R – fellow physics professor Dr. Randy Lewis. Together with his own team of researchers, Lewis predicts the numerical value of the pion form factor – precisely the same quantity that Huber and his team have now measured experimentally. Armed with Huber and his team’s snapshot, Lewis and his team will now have the opportunity to conduct further theoretical work and provide a clearer idea of the pion’s structure using a powerful technique called Lattice Quantum Chromo-Dynamics.

Together, the two teams are doing important work, says Zisis Papandreou, Head of the U of R Physics Department. “In their article, Dr. Huber and his international team of colleagues have published significant and unique data,” he says. “Based on these data, theorists can now develop more advanced models of the interactions between subatomic particles, helping change the way we look at the world – and the universe – around us. Indeed, the close collaboration between the teams of Dr. Huber and Dr. Lewis on the pion charge form factor and other research topics promises to shed new light on the forces that govern and determine the nature of matter.”

Huber is currently involved in plans to conduct additional experiments at the Jefferson Lab. These experiments would further measure and define the pion’s structure during its brief but significant 26-nanosecond existence.

Huber and his team’s article – “Determination of the Pion Charge Form Factor at Q2 = 1.60 and 2.45 (GeV/c)2” – can be found in the November 10, 2006 edition of Physical Review Letters.

For further information, contact Dr. Garth Huber at
(306) 585-4240 or huberg@uregina.ca.

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