by Tom Parisi
Physicists at NIU are watching with great anticipation as construction of the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland, nears completion. The project reached an important milestone recently, when the final piece of the ATLAS particle detector was lowered into the underground collision hall.
“To be involved in a project that is so massive in every sense is both uplifting and humbling at the same time,” said Physics Professor Dhiman Chakraborty, who leads a team at NIU that is contributing to the ATLAS project.
CERN, the European Organization for Nuclear Research, is the world’s largest particle physics laboratory. Experiments conducted at the lab’s LHC facility, poised to become the world’s most Npowerful particle accelerator, could help scientists unravel some of the deepest mysteries in particle physics. The U.S. branch of the collaboration, based out of the Department of Energy’s Brookhaven National Laboratory, built and delivered several key elements of the ATLAS detector.
Of the almost 2,100 participants in the ATLAS collaboration, representing some 180 institutions from 35 countries, about 420 are U.S. physicists, engineers and graduate students.
“The task ahead still looks daunting, but it is also exciting to be able to work with so many scientists and colleagues from all over the world and to share ideas and results with them,” Chakraborty said. His ATLAS team at NIU includes research scientist Guilherme Lima and two graduate students in physics, Rob Calkins and Chad Suhr.
The last piece of ATLAS lowered into the experimental cavern is one of two elements known as the “small wheels.” The small wheels, though little in comparison to the rest of the ATLAS detector, are each about 30 feet in diameter and weigh 100 tons. The wheels are covered with sensitive detectors that will be used to identify and measure the momentum of subatomic particles called muons that are created in LHC collisions.
The entire detector system has an area equal to three football fields, consisting of 100 million independent electronic channels. As charged particles pass through a magnetic field created by superconducting magnets, this detector has the ability to accurately track them to the precision of the width of a human hair.
The NIU physicists joined ATLAS in June and are now working closely with the ATLAS team at Argonne National Laboratory on remote monitoring and calibration tasks. Argonne has made significant contributions in all stages of acquiring, selecting, storing and accessing the data from ATLAS.
Chakraborty likened the detector, in very simple terms, to a huge microscope that takes pictures of sub-nuclear interactions at high energies. Calkins and Suhr are among the scientists who are responsible for calibrating and monitoring an important part of the detector, called the tile calorimeter, to ensure that it produces high-quality data reliably and consistently. Lima is working on computer simulations of particle detectors, which help scientists determine how the detector will respond to real events of particle collisions.
“The tile calorimeter spits out data through 10,000 channels at a very high rate,” Chakraborty said. “We need to certify that that data meets strict quality requirements. Through broadband computing, the detector’s performance in Switzerland can actually be monitored in real time in the United States.
“Initially much of this work will be done at Argonne,” he added. “At a later stage, some tasks may be moved to NIU.”
Beginning this summer, Chakraborty will be on leave from NIU for 14 months in order to collaborate as a visiting scientist with the ATLAS group at the French National Laboratory for Subatomic Physics and Cosmology (LPSC) in Grenoble, France, less than a two-hour drive from CERN.
The ATLAS detector, and another similar one called CMS, which will operate simultaneously at the LHC, could help scientists find answers to some of the most troubling and outstanding questions in particle physics and cosmology, such as the origin of mass and the identity of dark matter. The ATLAS collaboration will now focus on commissioning the detector in preparation for the start-up of the LHC this summer.
“This is a critical time, so we are approaching it with a mixture of excitement and nervousness,” Chakraborty said.
“So far there’s been nothing like the LHC in terms of scale when you consider the cost, state-of-the-art facilities, number of scientists and engineers involved, the time it takes to do these experiments, and the sheer size, muscle, complexity and speed of the gigantic yet super-sensitive apparatus. From conception to publication of all results through many hundreds of articles in scientific journals will take three to four decades,” he added.
Over the past two decades, the High-Energy Physics Group at NIU has established a strong track record of world-class research in experimental particle physics. Members of the group made major contributions to the DZero project at Fermilab’s Tevatron collider and to research and development for future facilities under consideration, such as the International Linear Collider.
“Our participation in the ATLAS project at the LHC is a natural continuation of that tradition and a significant step toward further strengthening of our research program,” Chakraborty said.
For more information, visit www.atlas.ch/.