Large Hadron Collider Study Supports Standard Model of Physics

Large Hadron Collider
A tunnel housing the Large Hadron Collider experiment at CERN near Geneva in 2014. Pierre Albouy/Reuters

The Standard Model of particle physics stands its ground again. As the Large Hadron Collider (LHC) embarks on its second run, a new study published Wednesday in the journal Nature combines data from two previous experiments from the Collider machine's first run to claim a discovery: the extremely rare decay of the "strange" B meson into a positive muon particle and a negative muon particle. The results are consistent with the Standard Model, the well-tested particle physics theory that explains fundamental particles and forces in the universe.

In the most basic terms, this particular decay process is predicted to occur just four times in every 1 billion decays, according to a press release from CERN in Switzerland. Though it had been previously suspected, it had not been confirmed with the statistical precision standard in experimental physics.

"It is testament to the excellent performance of the LHC, and the sensitivity of our experiments, that we have been finally able to observe this extremely rare but important decay," spokesman Guy Wilkinson is quoted as saying in the release.

This is the first time the very rare subatomic process can be said to be "discovered," explains Michael Tuts, chair of Columbia University's department of physics and a member of the Large Hadron Collider's ATLAS experiment team. The finding is a result of two other LHC teams (CMS and LHCb) combining their data from experiments conducted in 2011 and 2012. The teams had shared their individual results in 2013, but only combined could they surpass the accepted threshold of statistical certainty.

"There are a couple ways that we make discoveries in particle physics," Tuts explains. One, like the approach used in the monumental discovery of the Higgs boson, is to use the very highest energies to try to create new particles. "The other approach is to say, 'Let me look for very, very rare processes in our Standard Model of particle physics,'" like the strange B meson decay, Tuts says. "'If it deviates from what I expect, something else is happening.'"

In this case, there was no deviation from the theory. Though evidence in support of the Standard Model is "a great triumph," Tuts says, it is also perhaps disappointing to scientists, who have theoretical reasons to believe there are physics beyond the Standard Model and who are looking for evidence. The study published in Nature, alas, gives no such indication yet.