ATLAS detector ready to match large hadron collider improvements

More than 200 members of the ATLAS collaboration gathered on the Stanford campus last week to discuss how to make one of the world's biggest and best particle detectors even better.

ATLAS, one of the two primary detectors at the Large Hadron Collider, began taking data in earnest in March 2010 when the LHC started its first science run. Already, the collaboration has several ideas for improving the giant detector's abilities to capture information about the high-energy proton-proton collisions that are the LHC's stock in trade, said ATLAS upgrade coordinator Phil Allport, who is currently with CERN and the University of Liverpool. They'll have several opportunities to do so over the next decade, starting with Phase 0 upgrades during the LHC's planned shutdown in 2013 to prepare the accelerator to run at its intended energy of 14 TeV – 14 trillion electronvolts.

According to Allport, Phase 0 is a time of consolidation: "For the detector, it's an opportunity to correct known, minor issues and to significantly improve detector performance." The higher-than-expected luminosity, or total number of collisions, at the LHC has pushed the ability of the detector to capture all the data, but an even more important factor driving the planned performance improvements is the human element. "Much more important than the rise in accelerator luminosity is the ingenuity of the people getting information out of the collisions," Allport said. Better search strategies and more advanced analysis tools are yielding more data than expected from the collisions that ATLAS does capture.

After the 2013 shutdown, ATLAS scientists should have at least two more opportunities for major upgrades – Phase 1 and Phase 2 – if all goes as planned. Scientists hope to increase the luminosity of the LHC by a factor of 10 over current design luminosity, and at that point the ATLAS detector truly would not be able to keep up.

To compensate, during the Phase 1 upgrade planned for 2018, ATLAS is planning several projects to enhance the performance of the "trigger," the mechanism for identifying and capturing the most interesting particle tracks and the most important events. Phase 2 upgrades in 2022 will entail rebuilding much of the detector, especially the full tracking system and the electronics of most subsystems, to face the challenge of the much higher luminosity.

According to Allport, discussions about ATLAS upgrades started up long ago, and he's been involved "since the very first ATLAS meeting." He credits several of the United States collaboration members, including meeting hosts SLAC, Lawrence Berkeley National Laboratory and the University of California-Santa Cruz, as well as UC-Berkeley, with being among the first to think about what could be done to improve the massive machine.

However, one particularly gratifying aspect of the ATLAS upgrade is what the collaboration doesn't have to do: "To some of us, it's a surprise that things are working as well as they are," Allport said. "The upgrade is focusing on improving performance instead of responding to problems."