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October 16, 2012

Particle Physics

Large Hadron Collider Breakthroughs Excite CMU Physicists

By Jocelyn Duffy

It was a stellar day for physicists when researchers at CERN's Large Hadron Collider (LHC) announced that they found a particle with behavior consistent with that of a Higgs boson.

First theorized about 50 years ago, the Higgs boson was considered to be the missing piece of the Standard Model of particle physics - the framework physicists use to explain and interpret all the matter and forces in the universe. It's thought to be the particle that gives mass to matter.

CMU Physics professors Tom Ferguson, Manfred Paulini, Jim Russ and Helmut Vogel work on the collider's Compact Muon Solenoid (CMS) project. When the announcement was made this summer, Ferguson, Russ and Vogel were at the CERN facility in Geneva, Switzerland, that houses the LHC and Paulini had just left the facility and returned to Pittsburgh.

"It would be an understatement to say it was the talk of the town. People lined up outside of the main auditorium hours in advance," Vogel said. "This was the biggest event at CERN, and certainly one of the biggest in particle physics since the discovery of W and Z bosons 30 years ago."

The CERN facility is touted as the world's largest particle physics laboratory, where some 10,000 visiting scientists and engineers representing 608 universities and 113 nationalities come to work on their research aimed at answering some of the most fundamental questions of physics.

"You need this many people to design, build and run the experiment. You need this many people to check the quality of the data and to reconstruct and analyze the data," Paulini said. "The LHC produces between 10 and 15 petabytes of data per year. It's in these really huge sets of data where we hope to find the answers to some of our biggest questions."

"To recreate in the lab, however briefly, conditions like those in the first fraction of a second after the big bang require facilities and equipment that can only be designed and built by large international collaborations," Vogel added.

While the Higgs boson has grabbed much of the attention, it only represents a portion of the research happening at the LHC.  

"Finding the Higgs was a long-time milestone for the experiment. But this was not the reason the LHC was built," Ferguson said. "We know that the current Standard Model is incomplete. There are many extensions to the present standard model, most of which predict the existence of new particles.  We don't know which theory is correct - if any - so we don't know the mass or properties of the particles we are looking for. So the search continues."

The Mellon College of Science physicists are four of the many researchers working with the LHC who aren't searching for evidence of a Higgs boson. Early in the construction of the CMS experiment, CMU researchers under the leadership of Ferguson helped to construct the electronics for the CMS detector. Now they're using the data that comes from the LHC's high-energy particle collisions to try to find new particles, like yet-to-be identified quarks and supersymmetric particles.

"The opening of the new energy frontier at the Large Hadron Collider is an exciting time for particle physics," Russ said. "We're actively searching for new phenomena with the expectation that we will find evidence for a new class of particles."

Paulini and Russ are looking at data from the LHC to find something outside of the Standard Model that has eluded physicists for ages - a dark matter particle.

"We don't know what dark matter is. It doesn't interact with regular matter. It could be a new form of particle that possibly could be created at the LHC," Paulini said.

A good deal of this research relies on the theory of supersymmetry, which proposes that all particles have a counterpart that has the exact same mass and quantum number but differ in spin by one-half unit. During the LHC's high-energy collisions, new particles are created. As the particles decay it is thought that the last and lightest supersymmetric particle left could be a dark matter particle.

In their research, Vogel and Ferguson are trying to identify new types of quarks, the elementary particles that make up matter.

In addition to the scientific possibilities at the LHC, the CMU researchers also are excited about the educational opportunities. Currently three postdoctoral researchers, five graduate students and one undergraduate from CMU are working on projects with the LHC.

Historically, the skills the students learn on these large projects make them well prepared to address the challenges of applied science. Russ says that in the past 30 years, he's noticed that CMU students trained in high-energy particle physics are highly sought after by

"In the process of operating such complex experiments we've created a whole generation of highly trained experts in various technologies who will be sought after not just in academia but in industry," Vogel said.