Large Hadron Collider detects rare particle decay

Two experiments at the Large Hadron Collider at CERN have observed a previously unseen subatomic process that only occurs about four times out of a billion, an advance that may help explain the imbalance of matter and antimatter in the universe.

Researchers at the European Organisation for Nuclear Research (CERN) have observed a new and extremely rare decay of the Bs particle (a heavy composite particle consisting of a bottom antiquark and a strange quark) into two muons.

Theorists had predicted that this decay would only occur about four times out of a billion, and that is roughly what the researchers observed in data collected by the collider's Compact Muon Solenoid (CMS) and Large Hadron Collider beauty (LHCb) experiments in 2011 and 2012.

"It's amazing that this theoretical prediction is so accurate and even more amazing that we can actually observe it at all," said Syracuse University Professor Sheldon Stone, a member of the LHCb collaboration.

Scientists also saw some evidence for this same process for the Bd particle, a similar particle consisting of a bottom antiquark and a down quark.

However, this process is much more rare and predicted to occur only once out of every 10 billion decays. More data will be needed to conclusively establish its decay to two muons, researchers said.

LHCb and CMS both study the properties of particles to search for cracks in the Standard Model, the theory that best describes the world of particles.

The Standard Model is known to be incomplete since it does not address issues such as the presence of dark matter or the abundance of matter over antimatter in our universe.

"We know that Bs mesons oscillate between their matter and their antimatter counterparts, a process first discovered at Fermilab in 2006," Stone said. "Studying the properties of B mesons will help us understand the imbalance of matter and antimatter in the universe," he said.

The big bang that created the universe should have resulted in equal amounts of matter and antimatter, annihilating each other on contact. But matter prevails, and scientists have not yet discovered the mechanism that made that possible.

"The LHC will soon begin a new run at higher energy and intensity," said Fermilab's Joel Butler of the CMS experiment. "The precision with which this decay is measured will improve, further limiting the viable Standard Model extensions," he said.

The research was published in the journal Nature.