Finding declared a ‘victory’ for Standard Model of physics
The Large Hadron Collider at CERN
Physicists in are part of a global team of scientists that has discovered a rare particle decay, giving them an indirect way to test models of new physics.
Fifteen SU researchers, led by Distinguished Professor of Physics , have been working at , the world’s leading laboratory for particle physics, headquartered in Geneva, Switzerland. There, they have been involved with the , which seeks to identify new forces and particles, in addition to those already known and codified in the Standard Model, a theory which describes the physical makeup of the universe.
Stone and his colleagues have found evidence of particle decay made up of two kinds of quarks—bottom quarks and anti-strange quarks—that, in turn, form a pair of particles called muons.
A quark is a fundamental constituent of matter. A muon is a heavy electron.
Sheldon Stone
“The Standard Model predicts rather accurately that, out of a billion [particle] decays, there will be three where the quark-anti-quark pair transforms into a positive and negative muon,” says Stone. “The LHCb experiment has done this and has seen strong evidence for this decay, albeit at a rate predicted by the Standard Model. Small deviations from the predicted rate would firmly establish the presence of new forces or particles.”
That another LHC experiment—the Compact Muon Solenoid, or CMS—has produced similar results at CERN suggests the particle decay discovery is real.
Although physicists call the finding a “victory for the Standard Model,” they are quick to point out that the model is far from complete. In fact, Stone and his colleagues are eager to collect more data to see if small deviations from model predictions actually appear—clear indicators of new physics. “We keep trying to find things that disagree with it,” says Fermilab physicist Joel Butler.
“This latest measurement sets important new guidelines for theories of matter,” says A. Alan Middleton, professor and chair of physics at SU. “The ϲ group is already planning the next generation of technology, which will be built here and shipped to Switzerland to help solve these problems.”
Most of what is known about particle physics comes from high-energy particle accelerator experiments, such as the LHCb, which detect products of collisions from the LHC accelerator, the highest energy machine in the world. The LHC accelerates a fast-moving beam of protons and then smashes them into other protons moving in the opposite direction. These collisions form heavy particles not readily found in nature.
Since heavy particles are unstable and decay almost immediately, Stone and his colleagues have been searching for viable evidence of particle decay products, rather than the particle itself. In 2010, his team developed a special technique for measuring B meson yields, which has since been used by other LHC experiments.
“Fourteen billion years ago, the universe began with a bang, and matter and anti-matter were formed,” says Stone. “But just one second after the Big Bang, anti-matter all but disappeared. …The LHCb experiment is designed to find out what really happened after the Big Bang that has allowed matter to survive and build the universe we inhabit today.”
