The Standard Model of particle physics seemed to be complete with the discovery of the Higgs boson in 2012. Standard model is the best explanation physicists currently have for the basic building blocks of the universe and three out of four of the fundamental forces. But there are still a number of mysteries that the Standard Model simply cannot explain. These include dark matter and dark energy. Physicists supported by the Department of Energy (DOE) are trying to understand whether there are particles and forces beyond those in the Standard Model, and if so, what they are.
Nadia Strobe of the University of Minnesota Twin Cities is one of those researchers. She works on experiments at the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator of its kind. (The LHC is also where scientists discovered the Higgs boson.) The LHC is a 17-mile-long ring tube in Switzerland. It accelerates particles to 99.9999991% of the speed of light. At certain points, the particle beams collide and create spectacular sprays of new particles. The scientists collect data on the 40 million particle collisions that occur every second the machine operates. This data provides scientists with new insights into our universe. Some of the questions they investigate are why there is matter at all and why different particles have different masses.
Strobe, a professor of physics and astronomy in the University of Minnesota’s College of Science and Engineering, is looking a never-before-seen particle called a “top squark”. It is a theorized particle that would not fit into the current Standard Model of particle physics. The current standard model has 17 different particles. Some of them are particles that act as building blocks of matter. They include quarks that make up protons and neutrons as well as another group called leptons, which includes electrons. The Standard Model also describes particles that carry three of the four fundamental forces that govern the interactions between these building blocks. Long before experimental physicists found evidence for any of these particles, theorists predicted them. The Standard Model is like a crossword puzzle—the theory provides clues that allow physicists to “fill in” the gaps. The Higgs boson was the last gap to be filled.
Supersymmetry is one theory that may succeed in extending physics beyond the Standard Model. This suggests that there is a “superpartner” particle to every existing particle in the Standard Model. One of the existing particles in the Standard Model is called a top quark. The “top squark” that Strobe is investigating is the top quark’s theorized superpartner. Finding experimental evidence for a top squark could help scientists solve some of the problems that the current standard model doesn’t explain.
The LHC is essential to Strobbe’s work because it can potentially produce these supersymmetric particles. Scientists, including Strobbe, are using the LHC to collide protons in an attempt to produce these theorized particles. She recently received support from the DOE Office of Science to improve the way machine learning can interpret data from the LHC.
The LHC and Strobbe’s work are helping us better understand the foundations of the universe. They also set the stage for future technologies. The knowledge that scientists have gained from improving particle accelerator technology has proven essential to the development of medical technologies such as computed tomography and MRI. From the building blocks of matter to the technology we use to save lives, physicists are finding new ways to expand what we know about the world around us and beyond.