Physics, College of Arts and Sciences
Experimental high energy physics; experimental particle physics; Large Hadron Collider, solid state detectors for particle physics
More than 3,800 miles away and across the Atlantic Ocean from Cornell’s Physical Sciences Building is Geneva, Switzerland, the home of the European Organization for Nuclear Research (CERN) laboratory and the highest-energy particle accelerator on earth.
Cornell at CERN
Despite the distance, Cornell researchers are actively involved in the cutting-edge particle physics experiments taking place at CERN. Julia Thom-Levy, Physics, is one such professor. Thom-Levy has worked on the Compact Muon Solenoid (CMS) experiment at CERN’s Large Hadron Collider (LHC) since 2005.
Specifically, Thom-Levy is on a collaborative team of Cornell researchers who are responsible for developing software for the CMS detector, designing upgrades to the detector, and analyzing data collected by the CMS—all in search of new physics phenomena.
CMS is one of the two LHC detectors that led to the discovery of the Higgs boson (an elementary particle in the Standard Model of particle physics) in 2012 during the most recent LHC run. Since then, the LHC has been undergoing repairs. A second run took place during June 2015, with the LHC running at twice the energy, a major improvement that could lead to further discoveries.
“We are in an interesting situation here: a mathematical model—The Standard Model—explains all particle observations very well,” says Thom-Levy, who played a role in confirming the Standard Model to better precision over the past 15 years.
“It’s a very precise model. We know, however, that it doesn’t hold water, because we cannot explain certain important things like dark matter, or how exactly the Higgs boson ends up with the mass that we measure. There is a strange tension: on the one hand, we know what these particles do; we can predict it, but we don’t know why.”
Thom-Levy says that the second run of the LHC could reveal new particles, or inconsistencies in the data—“smoking guns” that will point scientists in the right direction. For example, they could find particles that might be consistent with supersymmetry, a proposed extension of the Standard Model, which could explain such mysteries as dark matter.
Dark matter in our universe has been elusive so far to detection—it does not emit or absorb light. Thom-Levy says that the LHC might, however, be able to produce dark matter, and that it is possible to observe it through its distinctive signature in the detector, which is the signature of nothing. One possibility is that dark matter consists of the lightest supersymmetric particles, and discovering it in the next run would be a huge boon to the researchers.
That said, Thom-Levy is cautious in her predictions. “I’m being very hypothetical,” she says. “The big glaring signature for supersymmetry did not appear in the first run. That was one of the surprises. It’s such a beautiful theory and we joke that it would be a shame if nature didn’t work that way. It’s something we will continue to look for.”
The Big Data Element
The Cornell CMS group—James Alexander, Richie Patterson, Anders Ryd, Peter Wittich, and Thom-Levy along with their students and postdocs—play a critical role in developing software to record and interpret the incredible amounts of data collected by the CMS.
Members of the Thom-Levy research group
When the detector is running, it records terabytes of data every day, and that data needs to be stored and distributed to various research institutions across the world for analysis. Researchers write programs to filter through trillions of proton interactions to get to the ones that are really interesting—ones that produce a Higgs or a top quark, for example.
“The most interesting interactions are often the most rare; they are the highest energy, highest masses, and very unlikely to be produced,” says Thom-Levy. “A lot of our field is like needle-in-the-haystack research.” Because of this, Thom-Levy says her students are exposed to “big-data,” and they learn how to handle and analyze huge volumes of data.
Students also spend time at CERN and learn how to make the detector work. Many of the group’s students are currently in Geneva, writing software for and testing electronics on the CMS detector.
Thom-Levy is also developing better detectors, using the latest cutting-edge materials and technologies. One challenge is that the particle’s high energies result in extremely high radiation levels, which damage the detector. As energy levels and particle density increase, the detectors need to become better at withstanding radiation, while still providing high precision measurements.
To address that and other problems, Thom-Levy is involved in a collaborative project testing the use of three-dimensional integrated circuitry for silicon detectors. She says that it could make detectors much thinner, use less power, and make them potentially stronger against radiation. So far, her group has simulated detectors and prototyped components at the Cornell NanoScale Science and Technology Facility (CNF). The next steps would be to work with more industry and university partners to hopefully build the next generation of detectors to be used at CERN’s CMS.
Pursuing the Universe’s Mysteries
Thom-Levy describes her journey to CERN as a sort of odyssey following the most interesting particle physics to various places. She started at Germany’s national accelerator lab, moved on to Stanford’s Linear Accelerator Center, off to Fermilab in Illinois, until finally landing at CERN. “With each move, the energy went up,” she says with a laugh.
When asked why she was drawn to particle physics in the first place, she gives credit to the local accelerator in her hometown. “I always knew I wanted to do sub-nuclear physics,” she says. “How does the nucleus work? What does it consist of? Can you break its constituents down, down, down? What’s the most fundamental unit in the universe?”
These are questions that are both scientific and philosophical to Thom-Levy. “We want to get to the very essence. It’s nothing we can touch, but the shadows of the mysterious workings of tiny particles may tell us about the most fundamental truth of the world.”
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