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Steve Chaplin
University Communications

Last modified: Wednesday, April 15, 2009

IU GlueX experiment advances with Department of Energy groundbreaking

New $14.1 million hall to be home for long-planned quark experiment

April 15, 2009

BLOOMINGTON, Ind. -- For more than a decade Indiana University physicists have only been able to theorize about the nature of exotic hybrid mesons, unique particles that may be the key to unlocking how quarks bind together to form matter's building blocks.

GlueX experiment

Participating in the groundbreaking at the U.S. Department of Energy's Jefferson Lab was Indiana University physicist Matthew Shepherd, fourth from right. Also pictured, from left, are Jefferson Lab director Hugh Montgomery, 12 GeV Upgrade project manager Claus Rode, Zisis Papandreou of the University of Regina, Curtis Meyer of Carnegie Mellon University, George Lolos of the University of Regina, 12 GeV Upgrade deputy project manager Allison Lung, Hall D scientist Elton Smith and interim Hall D leader Eugene Chudakov.

Print-Quality Photo

But the journey to move beyond theory in the search for these elusive particles moved a step closer Tuesday (April 14) with the turn of a shovel in Newport News, Va., where IU physicists were on hand to break ground on a $14.1 million, 8,000-square-foot experimental hall designed to test theories about exotic hybrid mesons. Mesons are particles made of a quark and an anti-quark that are bound together by gluons.

"This step is a huge milestone for our group and our colleagues working on this experiment," said Matthew Shepherd, an assistant professor of physics in the IU College of Arts and Sciences, and principal investigator on the IU portion of the GlueX experiment. "This experiment has only been a concept on paper that has been developed using a combination of computer simulations and small detector prototypes. To actually break ground and start construction is very exciting."

The new Hall D where the GlueX experiment is to be housed is part of a $310 million upgrade at the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility in Newport News. The project doubles the energy to which beams of electrons can be accelerated to 12 billion electron-volts.

Once completed, scientists will send the high energy electron beam through a diamond crystal to produce linearly polarized photons, which then hit a liquid hydrogen target. It is this combination of photon-proton collision that theorists predict is ideal for the creation of exotic hybrid mesons. The energy upgrade to the accelerator allows GlueX to search this unique and yet unexplored method of producing exotic mesons.

Scientists have studied the properties of many mesons to learn about both the nature of quarks and the interaction between them. In a meson, the gluons binding the quarks are thought to form a string, like a rope pulled taught between two people. It's the exotic mesons, where this string is vibrating -- as two people would swing a jump rope -- that is of special interest to physicists working on GlueX.

The GlueX experiment will help scientists describe quark and gluon interactions. The experiment will also help them better understand the phenomenon of confinement in which the strong force between quarks does not deplete as the quarks get farther apart, and instead acts like a rubber band -- preventing quarks from separating.

Studying results from the GlueX detector, Shepherd said, should aid scientists in developing a better understanding of the strong force behind the structure of the atomic nucleus, how that force confines quarks and how it contributes to the structure of everyday matter.

Much of the credit for IU's involvement at Jefferson Lab, according to Shepherd, goes to IU Physics Professor Emeritus Alex Dzierba, whose interest in the confinement of quarks led him to propose the experiment more than a decade ago.

"Alex is the one who took the idea of GlueX and worked with Jefferson Lab so that it became part of what is now known as their 12 GeV (gigaelectron volt) Upgrade," Shepherd said. "He was founding spokesperson and spokesperson for the first eight years of the experiment, and during that time a lot of the initial conceptual design work for the detector was done at IU."

At least 10 IU scientists, staff and students are currently working on the GlueX experiment, which has generated several million dollars in grants from the Department of Energy and the National Science Foundation. The team is currently finishing design and will begin construction on a $1 million calorimeter composed of 2,800 blocks of lead glass that will be used to detect photons produced when exotic mesons decay. The calorimeter is expected to be installed into Hall D at Jefferson Lab in 2012.

Additionally, researchers at the IU Cyclotron Facility have been refurbishing a 250-ton superconducting solenoid and supporting development of the drift chambers and their associated electronics for the GlueX experiment. Together these components are critical for tracking the charged particles produced in photon-proton collisions. Within its first year of use the detector is expected to collect so much data that it will exceed all currently existing data of this type by several orders of magnitude.

"Looking into the future, our goal is to ensure that the GlueX experiment has the highest probability of producing the exciting scientific discoveries that were initially imagined," Shepherd said. "Discovery of these particles would help validate our understanding of the theory of how quarks are bound together into larger structures."

To speak with Shepherd, please contact Steve Chaplin, University Communications, at 812-856-1896, or