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Professor speaks on Higgs boson

Megan Thomassen | Friday, September 7, 2012

Last night in the Jordan Hall of Science, Kevin Lannon, an assistant physics professor at Notre Dame, presented the fundamental principles of the research and technology behind the recent discovery of a Higgs boson particle.

The breakthrough was announced in Geneva on July 4. Lannon said it was the most significant scientific achievement in decades, and several Notre Dame professors, graduate and undergraduate students, were on location at the time of the announcement.

Lannon said the Higgs boson is the key to understanding the universe at its most fundamental level. “If you can understand the universe at its most basic level, and its most simple possible components, in principle, you can develop an understanding of everything,” he said.

“But we are still trying to find the bottom of the rabbit hole … We have more particles than we need to understand [the universe], but can we arrange them in a way that’s easier to understand?”

The Standard Model is the most successful theory in this respect to date, he said.

“It’s exciting because it makes a prediction,” Lannon said, “We are trying to fill out the Standard Model’s table of particles to see if we can validate this theory of how all these particles work together.”

Lannon said the Higgs boson is the last piece in the Standard Model puzzle. He used an analogy to describe the nature of the Higgs boson particle, whose main function is to give particles mass.

“The Higgs boson is like the paparazzi,” he said. “There is a sea of them filling all of space, and their effects depend on the person trying to pass through them.”

Photons, Lannon said, which are particles of light, can move through space at maximum speed, like an unknown bystander walking through a crowd of paparazzi photographers.

“And because the photon doesn’t react strongly to the Higgs boson, it has little to no mass,” he said. “But if a person interacts strongly with the paparazzi, like [former Irish football coach] Lou Holtz, he will have a harder time moving through … they’re swarming around him, he’s impeded, he can’t change direction. This is how the Higgs boson gives mass to particles.”

Lannon explained how the researchers in Geneva came to this discovery.

“Basically, we smash two protons together and get a Higgs boson,” he said. “But it weighs a lot more than two protons. We take their energy of motion and convert it into mass to make a bigger particle.”

The difficulty of finding proof for the particle is its short life span and speed, Lannon said.

“It decays into two other particles, like photons, way too fast for us to capture,” he said.

Lannon said the device capable of creating such a collision is the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) in Geneva. The accelerator is so large it cuts into French territory, and shoots particles at just eight meters per second slower than the speed of light, Lannon said.

“[I’s power is] the equivalent to an aircraft carrier moving at 3.8H [miles per hour],” he said. “Colliding protons is like shooting two needles at each other from six miles away and having them hit in the middle. This is something that’s done everyday at CERN.”

In order to capture the particle during its brief existence, Lannon said Notre Dame graduates collaborated with the scientists working on the Compact Muon Solenoid (CMS) to build a supersensitive camera. While the Higgs boson is only produced every three billion collisions, the accelerator is efficient enough to create nin9 Higgs boson particles per minute at its peak rate, Lannon said.

“Even high speed computing can’t record all the collisions,” Lannon said. “We need to analyze them as it’s happening.”

Both undergraduate and graduate students from Notre Dame helped develop the camera and the computers used to record the collisions, Lannon said. Once the researchers combined the data, science history had been made.

“They saw an excess of collisions with the Higgs boson signature, and they had their discovery,” Lannon said.

As for the future of particle research, Lannon said there was still more to understand about the particle. He said scientists had found two variations of the boson but were looking for three more.

“It should decay to a number of different particles,” Lannon said. “We can’t say we discovered the Higgs boson until we find all these variations of decay.”