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Steve Chaplin
University Communications

Last modified: Monday, November 23, 2009

IU physicists celebrate restart of world's largest particle accelerator

Nov. 23, 2009

BLOOMINGTON, Ind. -- Fourteen years and billions of dollars later, physicists at Indiana University today are celebrating their collaboration in the successful restart of the world's most powerful particle accelerator, the Large Hadron Collider at CERN laboratory near Geneva, Switzerland.

ATLAS experiment

The ATLAS Experiment at CERN,

The ATLAS detector at CERN, above, is a collaborative experiment involving Indiana University and 2,800 physicists from 37 countries and 169 institutions.

After more than a year of repairs, the LHC sent its first circulating particle beams around a 17-mile underground ring on Friday (Nov. 20). Then today (Nov. 23) scientists at CERN were literally raising toasts in the control room as the first low-energy collisions of proton beams occurred at the $5 billion particle accelerator.

For a team of IU physicists led by Harold Ogren and Hal Evans those first collisions marked 14 years of design, construction, testing and commissioning of an integral part of the collider known as the ATLAS detector. At 45 meters long, 7,000 tons and with a $540 million price tag, ATLAS is one of four major particle detectors that will gather untold amounts of data from high-energy particle collisions of magnet-guided protons that circle the 17-mile ring 11,000 times per second.

"We have been involved in this project since about 1995," said IU physics professor Harold Ogren. "We helped design the detector component (in ATLAS) and built a significant portion of the detector here at Swain Hall (home to IU's Physics Department). The six-foot diameter barrel detector is at the heart of the ATLAS experiment, located only about two feet from the interaction point where the two proton beams collide."

The "barrel" Ogren was referring to is the $11 million IU-constructed Transition Radiation Tracker Barrel (TRT), an integral part of the ATLAS detector that is one of three tracking systems used in combination with one another to precisely measure the curved path, and therefore the momentum, of the charged particles emitted from proton-proton collisions. The TRT uses straw detectors filled with Xenon gas (70 percent), carbon dioxide (27 percent) and oxygen (3 percent) to measure photons created when a particle passes between the straws.

As easy as it was to reflect on seeing ATLAS up and running, Evans recognized the LHC restart also marked what could be a future of unparalleled opportunities in scientific exploration.

"Our group at IU is anticipating surprises by working on ways to detect several possible new particles predicted by theorists. If we find them, these particles could mean that the universe has more than just three spatial dimensions," he pointed out. "Or they could turn out to be the "dark matter" that makes up 23 percent of the mass of the universe, but has not yet been observed. Or they could be a sign of an entire new type of "super-symmetric" matter. Needless to say, we're very excited to see what nature has up her sleeve."

"Today we've taken a big step toward that goal," Evans said. "We hope to take even bigger ones in the next few months."

Over the next few months, scientists will create collisions between two beams of protons, first at a relatively low energy of 900 gigaelectronvolts (GeV). They will then raise the beam energy, aiming for collisions at the world-record energy of 7 teraelectronvolts (TeV), or 7 million, million electronvolts, in early 2010. With these high-energy collisions, the hunt for discoveries like the ones referenced by Evans will begin at the LHC.

"The LHC startup initiates the data collection and analysis phase of our participation in the ATLAS collaboration," Ogren said. "We anticipate that this is the beginning of many decades of research at the highest energy accelerator in the world."

At IU, a team of four faculty members, three research scientists, three post-doctoral students and three graduate students worked on the ATLAS experiment. In all, an estimated 10,000 people from 60 countries have helped design and build the LHC accelerator and its four massive particle detectors, including more than 1,700 scientists, engineers, students and technicians from 97 U.S. universities and laboratories in 32 states and Puerto Rico, supported by the Department of Energy's Office of Science and the National Science Foundation.

To speak with Ogren, Evans or other IU physicists involved with ATLAS, please contact Steve Chaplin, University Communications, at 812-856-1896, or