The ATLAS detector under construction.
Image © CERN |
One of the discoveries eagerly anticipated by particle physicists working on the world's next particle collider is that of supersymmetry, a theoretical lost symmetry of nature. Supersymmetry, often called SUSY, predicts the existence of a superpartner particle for every known particle.
Why the big hunt for SUSY's "sparticles"? Recent experiments have suggested that most of the matter in our universe is not made of familiar atoms, but of some new sort of "dark matter." Discovering a hidden world of sparticles will shed light on the nature of this dark matter, connecting observations performed at earth-based accelerators with those performed by astrophysicists and cosmologists.
Physicist Sanjay Padhi, a Chancellor Fellow at the University of Wisconsin-Madison, searches for SUSY using the ATLAS detector at the Large Hadron Collider. Although the LHC and ATLAS won't start collecting experimental data until 2007, he and his colleagues are already hard at work generating the simulated data that is equally important to particle physics discoveries.
To discover evidence for SUSY, Padhi will compare data from the ATLAS experiment against simulations of what would be expected using the Standard Model—the conventional, well-understood model describing the physics of the universe. Simulating these expected Standard Model results requires innumerable numbers of particles to be generated and their interactions with all of ATLAS' many sub-detectors to be recorded and analyzed.
A simulation of an inclusive search for supersymmetry completed using grid resources. This plot shows a clear enhancement of the one-lepton supersymmetric signal (dots) over the background expected from the Standard Model (lines). Image Courtesy Sanjay Padhi |
"Simulation of these multijet events involves CPU-intensive exact matrix element calculations," said Padhi. "There were no dedicated CPU farms to complete these calculations, so to perform these studies I had to use the grid."
Accurately simulating the search for supersymmetry required Padhi to create a gateway to three different grid environments from his desk at CERN. He used the Virtual Data Toolkit to create an access point to resources from the Open Science Grid, LHC Computing Grid and the University of Wisconsin-Madison's Condor pool.
"The most difficult part was to make a grid which is interoperable, such that the requirements of all existing grid flavors could be included," explained Padhi. "This was done by modifying the current VDT, and I consumed more than 215 CPU years in less than two months using resources from OSG and Madison's Condor Pool."
With so many resources at his disposal, Padhi has simulated for the first time an accurate background for SUSY searches. His results show that there is a good possibility of discovering SUSY in the first few months of LHC operation, if the new symmetry exists in nature.
Learn more at the ATLAS and VDT Web sites.
—Katie Yurkewicz
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