UNL physicists gear up for upgrades to Large Hadron Collider

Particle Physics

Posted October 28, 2015 by jbrehm2 | View original publication

Compared with simulating millions of miniature Big Bangs – microcosms of the event believed to have spawned a universe more than 13 billion years ago – planning ahead a mere 10 years seems a pretty straightforward task.

Much like firing protons around the 17-mile ring of the Large Hadron Collider, however, prepping critical upgrades to the world’s premier particle accelerator is far from a straight shot.
From Oct. 19-26, UNL physicist Greg Snow joined hundreds of researchers at the CERN laboratory in Geneva, Switzerland, to discuss how the particle accelerator will progress over the next decade. While there, he attended various meetings that focused on U.S.-based contributions to future experiments.
The weeklong gathering marked the end of a four-year design phase for the High Luminosity Large Hadron Collider. By 2025, this series of improvements should allow the particle accelerator to produce roughly 10 times more particle collisions – and resulting data – than it does now.
Ramping up the particle smashing will offer more opportunities to detect rare phenomena while helping to refine measurements of the Higgs boson and other previous observations, Snow said.
“Our research group at UNL is very excited to be part of new discoveries foreseen to emerge using the new accelerator,” said Snow, professor of physics and astronomy.
Proton traffic camera
Identifying and measuring those discoveries will require upgrades to the Compact Muon Solenoid, or CMS, one of two massive particle detectors that helped confirm the existence of the Higgs boson in 2012. Snow spent much of his time in Geneva with teams of U.S. physicists who will help ensure that the CMS can handle the increased workload of the HiLumi Large Hadron Collider.
UNL is leading an $11.5 million effort to improve the pixel resolution and data-streaming capabilities of CMS components that track the trajectories of high-energy particles produced when protons collide. Without these improvements, the CMS would be overwhelmed by the sheer number of proton collisions to come.
Headed up by Aaron Dominguez, professor of physics and astronomy, the CMS detector upgrade should be completed by 2019. But in a move that exemplifies the five-steps-ahead mentality of CERN, Dominguez also recently agreed to help coordinate U.S. plans for a successor to the CMS module currently being assembled at UNL.
“Starting around 2025, we will upgrade the accelerator complex again and have a shutdown where we remove the current detector – which we’re busy building downstairs in Jorgensen Hall – and install another one,” Dominguez said. “Because of the time lag involved in research and development, we have to start thinking about that now, even while we’re building the detector that we will eventually tear out.”
Thinking that far ahead, Dominguez said, demands foresight that accounts for financial and time constraints. The team will have to strike a balance between pushing practical limits and minimizing the risk of costly failures, he said.
The researchers will also do their best to project how new findings and technology improvements might shape what the field of particle physics will look like – and what it may need – a decade from now.
“Things change a lot in that amount of time,” said Dominguez, whose colleagues also include UNL’s Dan Claes and Ilya Kravchenko. “Ten years ago, there were no iPhones. Now everybody’s got one.
“We do have some idea of how technology progresses, but you just can’t predict exactly what’s going to be happening. So we also have to try to be nimble (enough) to take advantage of gains: some new technology or new advance or new idea. That’s the stage we’re in right now.”
Setting the standard
UNL’s Ken Bloom, who serves as manager of software and computing for the U.S. CMS operations program, said better understanding the Higgs boson will represent a major goal for physicists working at the HiLumi Large Hadron Collider.
In the predominant Standard Model of particle physics, the Higgs boson explains how elementary particles – the building blocks of all matter – gain their mass. A universe without the Higgs force field would be unrecognizable, though humans wouldn’t even exist to question the strangeness of it all.
“We certainly believe that the Higgs has been discovered, but the properties have not been nailed down to any great precision,” said Bloom, associate professor of physics and astronomy. “Everything that we’ve seen is consistent with what we’d expect from a Higgs boson in the Standard Model, but all these measurements are sort of at the 20 or 30 percent level.
“It’s such an important particle within physics that we want to understand it as well as possible. That’s really something that we’re going to be pursuing in the current and future data.”
Yet the search for what has gone unobserved, especially the mysterious dark matter believed to constitute more than one-fourth of the universe, will also receive serious attention in coming years, Dominguez said.
Because it does not emit, reflect or absorb light, dark matter cannot be seen. However, its existence has been inferred from the fact that rapidly rotating galaxies would tear themselves apart if held together only by the gravity of visible matter.
“When you add up all of our best world knowledge that we’ve accumulated over the past 50 years or so, it still describes only about 5 percent of the matter and energy content of the universe,” Dominguez said. “If you were my student in a physics class, and you took an exam where you got 5 percent out of 100, you’d probably get an ‘F.’
“So that’s one of our big, outstanding questions: Can we produce and directly (detect) some dark matter particles in our collisions at the accelerator? That’s an exciting thing.”
Dominguez said physicists will also use the upgraded accelerator to try reconciling gravity with the Standard Model, which has yet to reliably account for the force at the quantum level of sub-atomic particles. One theory suggests that gravity escapes to other dimensions whose existence would be supported if certain particles are eventually detected by the CMS.
“We’re basically trying to do everything,” Dominguez said with a laugh. “We’re trying to take as full advantage of this opportunity as possible.”