Gulps from a fire hose: Sifting particle collisions in the Large Hadron Collider

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By Roger Snodgrass

A computer device built at Los Alamos National Laboratory will play a role in the hunt for a missing particle known as the Higgs Boson, when the Large Hadron Collider begins to power up next month near Geneva, Switzerland.

The LHC, 17 miles in circumference, is about to become the biggest and most energetic atom smasher ever built. Supercooled, synchronized magnets will steer protons going one direction into protons going the other at nine-tenths the speed of light, producing seven times the energy of the existing Tevetron at Fermi Laboratory and creating a chaotic storm of some 600 million subatomic collisions a second.

“The central problem with a big science detector is that it is literally impossible to store all the information coming out,” said Matt Stettler of the laboratory’s International, Space and Remote Sensing Division. “You have to figure out on the fly what’s interesting and what’s not.”

The Los Alamos contribution, in collaboration with the University of Wisconsin and the Imperial College of London, among others, amounts to a “real-time supercomputer,” able to network enormous volumes of information (40 terabytes per second) as they arrive, so that trigger arrays can instantly recognize the data most likely to be worth saving.

The computer card that makes this possible is an evolution of an electronic device developed by the laboratory for a space satellite with a similar requirement for processing a flood of incoming information before relaying the most important information by a narrow bandwidth back to earth.

Researchers hope that some small portion of the proton collisions in the LHC will create a particle known as the Higgs Boson and that the event will be “seen,” despite the noise and debris of all the other collisions.

The Higgs Boson is named for the British scientist Peter Higgs who first hypothesized that such a particle could explain how mass exists in the universe.

“It’s the only particle in the standard model that we haven’t found,” said John Jones, a Princeton University physicist who has a leading role in tracking the tiniest traces of the wreckage. “But we know where to look.”

Jones gave a recorded presentation at LANL earlier this month on his project involving the Compact Muon Solenoid (CMS), one of the two main general-purpose physics experiments in the collider. The solenoid in the CMS measures the momenta of scattered particle from collisions at the terascale, in the trillions of electron volts, the region of energy where the scientists expect to find the next dimension of the properties of the physical world. “The LHC is the last hope to find this particle if it exists, or we have to start rethinking our theories,” Jones said.

Jones compared the search to the classic problem of finding a needle in a haystack.

The complete system integrates the information from four levels of sensors, and two layers of triggers to capture the essential data, based on the recognition of particle signatures, patterns and tracks.

The team is working on the next generation of triggers to increase the “haul” of info by another factor of 10 in the next few years.

In its search for new phenomenon, the $8 billion LHC operates at a temperature just 1.9 degrees Celsius above absolute zero.

According to plan, the underground ring that contains the particles should be fully cold by the end of July, followed by gradual powering up and elaborate checks and tests in preparation for beam.