Is Particle Physics About to Rewrite the Standard Model? Not So Fast…


A new subatomic particle observation is leading some scientists to question the Standard Model. PASIEKA/Getty Images
A new subatomic particle observation is leading some scientists to question the Standard Model. PASIEKA/Getty Images

"In light of the latest analysis on the decay of beauty mesons, the dawn of a new era, that of 'new physics,' may be approaching." So proclaimed a recent statement from Poland's Institute of Nuclear Physics.

Now, if you're not a particle physics buff, you might guess that a beauty meson, also known as a B meson, is some sort of exotic cosmetic treatment. Actually, though, it's a type of subatomic particle, and according to the Standard Model of particle physics — the 40-year-old theoretical framework that describes the fundamental interactions of various building blocks of matter and elementary forces — beauty mesons should decay at very specific angles and frequencies.

"It is extremely hard to come up with an entirely new framework."
John Campbell, Fermi National Accelerator Laboratory theoretical physicist

What researchers have discovered in recent years, though, is that beauty mesons don't seem to quite match up with predictions based on the Standard Model. The institute's press release, for example, calls attention to 2011 and 2012 data from the Large Hadron Collider, the facility along the French-Swiss border that is the world's largest and most powerful particle accelerator. A new method of analyzing the data, proposed by Polish physicist Marcin Chrząszcz, indicates that the beauty meson's angle of decay is different from what the Standard Model would indicate.

Chrząszcz emphasizes that in the world of physics, the new finding doesn't qualify as a "discovery," because the deviation isn't sufficiently large.

"This is what we call an observation," he clarifies in an email.

Even so, the discrepancy adds at least some momentum to the notion that the long-established Standard Model might need at least a little revision. While most ordinary people probably have never heard of it, the Standard Model explains the reality around us at the tiniest, most basic level. The theoretical framework describes how the basic building blocks of matter — the fundamental particles —are governed by forces such as electromagnetism.

The Standard Model "has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena," says the website of CERN, the European physics research organization which operates the Large Hadron Collider. "Over time and through many experiments, the Standard Model has become established as a well-tested physics theory." (If you want more details, check out CERN's primer on the Standard Model.)

But while the Standard Model has been really useful to physicists, they've been aware for a while that it doesn't explain everything about the subatomic realm. As CERN notes, the theory only accounts for three of the four fundamental forces, by omitting the influence of gravity. It also doesn't explain phenomena such as the nature of dark matter, the mysterious mass that along with dark energy, makes up 96 percent of the universe. There's the question of how newly-discovered particles might fit into the theory. And finally, there's also the murkiness that remains around the Higgs boson, a particle that's an essential component of the Standard Model. 

In 2012, researchers using the Large Hadron Collider announced that they'd discovered a particle that seems to be the right one, but the case isn't quite closed yet. "This particle is consistent with the Higgs boson but it will take further work to determine whether or not it is the Higgs boson predicted by the Standard Model," CERN's website explains.

So does that all mean that it's time to throw out the Standard Model and start over? Not hardly. John Campbell, a theoretical physicist at Fermi National Accelerator Laboratory, the top U.S. particle physics laboratory, explained via email that scientists might just need to tinker with it a bit.

"Any alternative must account for a wealth of experimental observations that have been made over very many years," he says. "It is extremely hard to come up with an entirely new framework that explains all the observed phenomena in as successful a manner as the Standard Model."

Instead, he says, the best approach may be to add on "extensions" that describe new particles and the ways in which they interact with ones already in the Standard Model.

"There are many possible extensions," says Campbell, "but their number is greatly reduced by the requirement that they must not introduce effects that would be inconsistent with observations so far."

The most significant extension probably would be one that explains dark matter within the framework of the Standard Model. Such a discovery "would have a profound impact," he says, "not just in particle physics, but in cosmology as well. Suspecting the underlying theory of dark matter, we would be able to precisely compute its expected effects. For instance, we could better understand how we might be able to observe it directly, and also how its presence is imprinted on the cosmos."