SCIENCE

U.S. physicists have begun work on a new particle detector that will be the first major upgrade for the Large Hadron Collider (LHC). A $3.5 million grant from the National Science Foundation (NSF) is funding a consortium of 11 universities led by the University of California, Santa Cruz, to work on the detector.

Called the Insertable B Layer (IBL), the new detector consists of a layer of particle-tracking sensors that will be installed inside the ATLAS detector, a massive instrument with multiple layers of devices to track and measure the jets of subatomic debris generated by high-energy collisions of proton beams within the LHC. The LHC has just concluded a record-setting initial run of high-energy proton collisions. Physicists are looking forward to a longer proton-collision run next year that will generate even more data.

"The machine is doing great, and everyone is upbeat about the potential for new discoveries," said Abraham Seiden, professor of physics at UC Santa Cruz and principal investigator of the NSF-funded consortium. "This new detector is a way to look more deeply at what we see initially or, if we don't see anything, to keep searching."

Seiden, who oversees U.S. participation in the overall effort to develop upgrades for ATLAS (one of two general-purpose detectors at the LHC), said the IBL is planned for installation in 2015. The consortium working on it includes researchers at UC Santa Cruz, UC Berkeley, Brandeis University, Ohio State University, Oklahoma State University, SUNY Stony Brook, University of Hawaii, University of Iowa, University of New Mexico, University of Oklahoma, and University of Washington. The researchers will also be working in collaboration with Lawrence Berkeley National Laboratory, the Stanford Linear Accelerator Center, and European research institutions.

The IBL will use new technology that was not available when ATLAS was being built, which will allow the device to be placed inside the innermost layer of the current ATLAS detector, closer to the beam pipe where the particle collisions take place. The collisions generate sprays of rapidly decaying subatomic particles, and physicists use data from the detectors to reconstruct what happened inside the beam pipe.

"Moving closer to the beam is one of the main goals, because as you move closer you're able to see the interaction closer to where it's occurring, so you can tell much better what happened," Seiden said.

One downside of placing a detector layer close to the beam is the intense exposure to damaging radiation. The new system will be designed to withstand a radiation dose 10 times higher than the current system can handle. Three candidate technologies are being considered for the sensors, including a three-dimensional silicon pixel sensor that could prove to be especially resistant to radiation damage, Seiden said.

Advanced technology will also be used for the electronic "readout" chips that process the signals and send them to a central computer system for storage and analysis. With design improvements and advances in chip technology, the new readout chips will be much faster, allowing the IBL to handle 10 times more data than ATLAS's current inner detector layer.

The IBL will improve the overall performance of ATLAS. In particular, it will provide greater sensitivity in the search for the elusive Higgs boson, a major goal for the LHC. A theoretical particle predicted by the standard model of particle physics, the Higgs boson may hold the key to understanding what gives elementary particles their masses. Physicists are also hoping the LHC will deliver clues to new kinds of physics, from supersymmetry to dark-matter particles.

Seiden and his colleagues at the Santa Cruz Institute for Particle Physics (SCIPP) have been involved in the ATLAS experiment since 1994. Their work focused on the inner tracker, including the silicon sensors and readout electronics. This early work, as well as the new project to develop the IBL, has provided many opportunities for UCSC undergraduates and graduate students to work on a major international physics experiment.

"We began doing research and development for this upgrade four years ago, and we have had undergraduates and graduate students working on it all along," Seiden said. "The immediate tasks they are helping with are testing the detectors and conducting radiation exposure tests."

Operated by CERN, the European particle physics lab based in Geneva, the LHC is located on the border between Switzerland and France. More than 1,700 scientists, engineers, students, and technicians from 89 U.S. universities, seven U.S. Department of Energy (DOE) national laboratories, and one supercomputing center helped design, build, and operate the LHC accelerator and its four massive particle detectors. American participation is supported by the DOE's Office of Science and the National Science Foundation (NSF).