Measuring Up
Robert H. Lee receives first Ph.D from US-CMS research

by Mike Perricone

Physics is the science of measurement, and measurement relies on unchanging standards—the inch, the centimeter, the second, the electron volt. But what if a standard is distorted and unreliable? How can a measurement be accurate?

Graduate student Robert H. Lee of Purdue University confronted that issue in the design and construction of the endcap muon chambers of the Compact Muon Solenoid, the advanced detector destined for the Large Hadron Collider when it begins operation later this decade at CERN, the European Particle Physics Laboratory in Geneva, Switzerland. Fermilab is the host lab and project manager for US-CMS, charged with constructing and delivering major components of the detector to CERN.

“The CMS detector is essentially a large magnet surrounded by muon chambers,” said Lee, outlining the problem. “It’s a novel experiment in that we’re measuring muons in the most forward regions. CMS uses a four-Tesla magnet—a huge magnetic force. The muon chambers located on the ends of the magnet are attached to iron disks. When the magnet turns on, we expect the force to pull the disks in by a couple of centimeters, as well as move them as much as three millimeters in the X and Y planes. The bottom line is—if we don’t know where the chambers are, we’re not going to do a very good job measuring muons.”

To understand the processes taking place at the core of high-energy collisions at the LHC, scientists need to trigger on and measure the tracks of particles escaping the collisions, such as muons, with great precision. Knowing the exact location of all detection devices is imperative. Lee’s work was an analysis and simulation of an alignment system to keep track of the location of the iron disks and a number of the muon chambers with periodic measurements. Lee’s work resulted in a thesis: “Simulation and Study of the CMS Endcap Muon Alignment Scheme.” In May 2002, Lee’s Ph.D. became the first generated by research on the US-CMS Project.

“The first Ph.D. from a new program is a significant milestone for our laboratory,” said Fermilab Director Michael Witherell. “It’s one more sign that the US-CMS collaboration is already completing large parts of its work in building the detector. We know this step is just the beginning of great things to come, as well as the first of many Ph.D.s to be based on research with CMS. Fermilab and the US-CMS collaboration will take advantage of the great discovery potential of CMS in the years to come. On behalf of the lab, I congratulate Robert Lee.”

Lee’s thesis focused on three major areas: designing the system and testing out individual components; simulating the entire system in CMS, which involved co-authoring software; and simulating the impact of the alignment system on the physics expected at the detector. Testing the components involved a trip to CERN, where a scale model of the system was built and surveyed with photogrammetry, a process that uses a series of overlapping photographs for precise alignment measurements.

“In the completely assembled CMS detector, of course, photogrammetry will be impossible,” Lee said. “All of the muon chambers are embedded between layers of iron. There are no clear lines of sight, so you can’t use it. The detector will be put together on the surface, then taken apart, then dropped several hundred feet down the shaft, and reassembled in the tunnel. You expect things to get shifted around in a big move like that. Then when you turn on the magnet, things really get scrambled up.”

Lee worked closely with Fermilab physicist Dave Eartly on the CMS project, beginning as a Purdue undergraduate. He offered major thanks for support from US-CMS physicist Kaori Maeshima, member of Lee’s thesis committee, and from Hans Wenzel of Fermilab’s Computing Division. His major advisor at Purdue, Laszlo J. Gutay, also played a major role in an unusual way: helping convince the U.S. Air Force to wait four years for Lee to report for duty, which he did on July 12.

“It’s very unusual for the Air Force to do that, and it’s the first time it’s ever been done at Purdue,” said Lee, who had been commissioned after serving in the Air Force Reserve Officers’ Training Corps. “The biggest issue is that no professor can guarantee that you’ll get a Ph.D. in a certain amount of time. We had to find a project where it was certainly possible to do it in four years.”

Lee is stationed at Wright-Patterson Air Force Base in Dayton, Ohio, conducting research on propulsion systems ranging from conventional combustion to rockets to ion propulsion techniques. His wife, Angela, is a clinical pharmacist, and they’ll look forward to settling in Dayton for the next four years, while Lee decides whether to make the Air Force a career.

Lee is the product of a military family. His father was an Army helicopter pilot; Robert grew up in locations ranging from North Carolina to Washington, D.C., to St. Louis, where he graduated from high school. His grandfather, whose family originated in Virginia, was also in the military, and all three generations carry the name Robert. With good reason: their ancestry traces back to General Robert E. Lee.

“Some of our family heirlooms are a tapestry that belonged to him and silverware bearing his initials,” Lee said. “I’m certainly proud to be related to someone of the stature of Robert E. Lee. On the other hand, we still have to pay admission to the Lee family museum in Virginia.”