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Researcher assists in particle decay discovery at CERN

With the discovery of a rare particle decay at the CERN laboratory in Geneva, Switzerland, physicists have a new incentive to continue exploration of the standard model of particle physics — and campus scientists had a direct hand in the discovery.

Jose Lazo-Flores, a postdoctoral researcher with UNL's high energy physics group, is stationed at CERN and helped analyze the data amassed as physicists observed a rare particle decay that had been sought for more than a quarter-century.

The observation follows last summer's discovery at CERN of the long-theorized Higgs boson particle and helps explain the origin of particle masses and the early universe.

The particle is known as "B-sub-s," an unstable, electrically neutral and very short-lived particle that has been produced and studied via colliders for decades. It has been observed to decay in dozens of different ways. Physicists have predicted through the standard model that B-sub-s should decay into two muons (elementary particles similar to electrons) very rarely, only three times in every billion decays.

After 26 years of research into this phenomenon, scientists working on the Compact Muon Solenoid experiment at CERN's Large Hadron Collider were able to prove this hypothesis. It further cements the standard model as the theory that explains the basic building blocks of matter and interactions of subatomic particles while ruling out other models and opening possibilities for new directions of study.

"The standard model of particle physics is the most successful theory that has been formulated," Lazo-Flores said of the discovery. "So far, all of its predictions, those that we have been able to probe, have been observed. However, the theory is not complete. It does not include gravity or dark matter, for example, so there has to be a theory that is more complete."

Lazo-Flores said this discovery offers a "narrowing" of theories that attempt to complete the standard model.

"One of these theories is called supersymmetry, and different versions predict either an enhancement or a suppression of the B-sub-s to muon-muon decay rate relative to the standard model," he said. "One of the impacts of this observation is that theorists can now tune this theory to match the observation.

"In other words, extremely rare decays like the B-sub-s to muon-muon make excellent probes for new physics. This is the reason why so much effort has been spent by many researchers over the last quarter century."

Lazo-Flores said this discovery goes hand-in-hand with last year's announcement of the discovery of the so-called "God particle" — the Higgs boson — in adding more certainty to scientists' thinking about the creation of matter.

"This observation also gives us confidence that the standard model is accurately describing the universe up to when it was about a pico-second old, or 0.000000000001 seconds after the big bang," he said. "The Higgs boson discovery and the B-sub-s to muon-muon observation are both pieces of the puzzle that we are putting together.

"Both of these observations narrow down the places where a new theory that completes the standard model could be hiding."

The UNL high energy physics team studies the fundamental constituents of matter through experiments at the world's highest-energy particle accelerator laboratories, including work on the CMS experiment. The UNL team also includes faculty members Ken Bloom, Dan Claes, Aaron Dominguez, Ilya Kravchenko and Greg Snow, plus several other researchers working in Lincoln, at CERN and at the Fermi National Accelerator Laboratory in Batavia, Ill.

— Deann Gayman, University Communications