A Princeton University undergraduate working on her senior thesis found a bug in one of the detectors at the Large Hadron Collider (LHC), the gargantuan particle accelerator set to come back online before the end of the year. The Daily Princetonian reported this week that Xiaohang Quan "discovered errors that were leading to the appearances of double images" in the LHC's Compact Muon Solenoid (CMS) experiment and that Quan presented suggestions for how to fix the problem to scientists at CERN, the European lab for particle physics that operates the collider near Geneva, Switzerland.

But how common are such errors, and how worried should we be that a student, rather than a professional physicist, stumbled across one?

John S. Conway, a University of California, Davis, physicist (and Cosmic Variance blogger) who is part of the CMS team, says that finding such glitches is common and not cause for concern. He says Quan found "a bug in the software we use to reconstruct events" that "would have been found very quickly by any one of hundreds of other people who are testing our software every day." All the same, Conway says, "clearly this is a talented undergrad."

He adds that, alas, researchers working on the LHC "still have many, many software errors to find and correct in the coming months and years." The big ones, such as the snag Quan uncovered, will become apparent quickly. "Other bugs lead to rare or subtle effects that frankly we probably won't see until we start getting real data," Conway says. "But we will, and we will fix them."

Princeton physicist Christopher Tully, Quan's thesis adviser, sounded a similar tone in the Princetonian. He told the paper that "improvements to the algorithms are part of a normal process of scientific investigation that serve to improve the performance of the detectors." This kind of work, Tully added, "is business as usual for the physicists."

Photo of part of the CMS under construction in 2007 © CERN