UCSD Physicists Take Part in World’s Largest Experiment

Kim McDonald | September 22, 2008

UCSD researchers examining first beam data

UC San Diego physics professor Frank Wuerthwein never thought his work as a particle physicist would be front page news. But when the world’s largest particle collider turned on its beam of protons near Geneva on September 10, Wuerthwein began receiving text messages from people he hardly knew congratulating him on the accomplishment.

“I have never in my life seen my field attract so much attention,” he said with amazement on his way to the airport for his 20-hour flight to Geneva.

Wuerthwein is one of 24 UCSD physicists involved in the Large Hadron Collider, or LHC, which this month begins the long-awaited quest to find the Higgs boson, a hypothetical particle that physicists hope will allow them to finally tie together the fundamental forces and particles in nature into one grand theory. It is the world’s largest experiment, 15 years in the making and involving an estimated 10,000 individuals from 60 countries, including more than 1,700 scientists and engineers from 94 U.S. universities and laboratories.

Since 1994, UCSD physicists have been shuttling between La Jolla and Geneva during their sabbaticals and teaching breaks to work on one of the European collider’s two big particle detectors—the Compact Muon Solenoid, or CMS. Make that a gigantic particle detector.

“The CMS detector is 15 meters in diameter and weighs around the same as 30 jumbo jets or 2,500 African elephants,” said Vivek Sharma, a professor of physics who participated in the LHC’s historic grand opening. “And though it is the size of a cathedral, it contains detectors as precise as Swiss watches.”

Simulation of what the Higgs boson might look like

Because of the huge volume of data expected from this experiment, the UCSD team has designed and built the largest data acquisition system in the world to analyze the more than 100,000 collisions per second that will be generated when beams of protons circulating at nearly the speed of light in opposite directions around the 27-kilometer LHC ring are brought together in violent collisions.

“When the two proton beams collide, they will generate, within a tiny volume, temperatures a billion times hotter than in the heart of our Sun,” said Sharma. From those fireballs of pure energy will emerge particles never before seen on Earth that will exist for only the briefest fraction of a second, but long enough to provide physicists with clues to improve on their basic theory of nature—what they call the Standard Model.

Sharma said the detector itself is capable of operating like a 70-megapixel digital camera taking 40 million photos a second. And the 15 million Gigabytes of data expected to be generated each year by the CMS experiment will produce the equivalent of 20 million CDs of data that will require the computing power of about 100,000 of the fastest PC computers.

“This is a seriously big electronics experiment,” said physics professor James Branson, the most senior member of the UCSD team who joined the project in 1994, when the U.S. abandoned construction of the Superconducting Supercollider, a bigger version of the LHC in Texas. He noted that much of the data from the CMS experiment will be analyzed by newly installed computers in Mayer Hall. “In the past, we’ve had to do the data analysis at the laboratory,” he said. “But we now have a computing center that has lots of power.”

The CMS detector

Does that mean it’s possible that the first sighting of the Higgs boson—the Holy Grail of physics or what some have termed the “God particle”—could occur at UCSD? Possibly, although Branson said months or even years of statistical sampling from millions of proton collisions will be required before anyone could claim to have found the Higgs. The physicists also face a slight delay in their experiment after a mishap on Friday damaged one of the collider’s magnets.

“Finding one Higgs particle will require carefully sifting through more than 10,000,000,000,000 proton-on-proton collisions,” said Sharma.

Find out more about the LHC and UCSD’s role in the CMS experiment from this blog by Darin Acosta, a former UCSD graduate student now at the University of Florida: http://cmsdoc.cern.ch/cms/performance/FirstBeam/cms-e-commentary.htm