Physics Beyond the Standard Model

The Large Hadron Collider (LHC) at CERN in Geneva, Switzerland, is the world's most powerful particle collider. The LHC is capable of detecting the presence of infinitesimal particles that only exist for a fraction of a nanosecond. From these traces, physicists try to understand what makes up the universe at the most fundamental level.

One of two large, general purpose detectors at the LHC, known as ATLAS (A Toroidal LHC ApparatuS), was designed to observe some of the tiniest, yet most energetic, particles ever created on earth. It was one of the two LHC experiments involved in the discovery of the Higgs boson in July 2012.

ATLAS is a physical instrument, but it requires enormous amounts of computing power to interpret its results. Analyzing the signals of particles spewed out during collisions; reconstructing the reactions that led to the outburst; and developing models that explain what happened, are all major computational challenges. A world-wide network of advanced computing systems collaborates on this effort.

In the coming years, the ATLAS team plans to ramp up the number of collisions it produces by a factor of 10. With this increase in activity comes a corresponding need for significantly more computing power.

This is an area where TACC and Frontera will help. In 2017, the ATLAS team began using Stampede2 to run event generators, work that will increase on Frontera.

"We simulate the detector response to a given physics model," said Robert Gardner, a research professor in the Enrico Fermi Institute at the University of Chicago who co-leads the distributed computing facility group for the U.S. ATLAS collaboration.

"When we're doing the analysis on the actual data, we may plot some distributions such as the particle mass, transverse momentum, or the ‘missing energy' in the collision. And you get the number of candidates that we have for the raw data coming off the detector. Then we compare those to different kinds of models and see if we can match up the distributions. This provides clues to what might be actually happening during the collisions."

The Higgs Boson was the last building block predicted by the Standard Model, which explains three of the four fundamental forces in the universe, but not gravity. However it is likely not the end of the story. "Our observations only account for about five percent of the energy thought to make up the universe," Gardner explained. "There's a huge component out there that is yet to be discovered, and some believe dark matter might provide some of this missing energy. ATLAS has the means to hunt for signs of new types of matter created in LHC collisions, but we need large scale computing and analytics to interpret the data."

Frontera will be useful not only for particle physics, says Gardner, but for all types of ‘long-tail science'.

"We need systems like Frontera to answer the big questions of our time, such as the sustainability of the environment and renewable energy," he said. "We have to continue to work on frontier science and everything that comes after it, and we can't do that without computation."