Scientists have revealed that it is unlikely that a new particle will join the family of neutrinos, despite encouraging early signs.

As it stands we know of three neutrinos: the muon neutrino, the electron neutrino, and the tau neutrino. It was thought that a fourth “sterile” neutrino may exist, but a new study has poured cold water on the idea, writes Roya Sabri for The Christian Science Monitor.

Sterile Neutrinos
Image source: Wikimedia Commons

Potential for game-changing findings

This Monday scientists from the IceCube Neutrino Observatory released a study that shows that it is unlikely that a sterile neutrino exists. Other neutrinos rarely interact with matter, but the sterile neutrino was thought to hardly react with matter at all.

“Like Elvis, people see hints of the sterile neutrino everywhere,” Francis Halzen, a University of Wisconsin-Madison professor of physics and principal investigator for the IceCube Neutrino Observatory said in a statement. “There was this collection of hints, and theorists were convinced it exists.”

If researchers had been able to find a fourth neutrino it would have led to a complete rethinking of the Standard Model of particle physics. “If you throw in a fourth neutrino, it changes everything,” said Professor Halzen.

Lack of evidence leaves further questions

Even though it has been confirmed with 99% certainty that there is no such thing as sterile neutrinos, physicists still have to think about what may need to be added to their simplest models.

“It could be just that nature is much more complicated” than we think, said Janet Conrad, a physics professor at the Massachusetts Institute of Technology.

The search for sterile neutrinos was carried out by the IceCube Neutrino Observatory, which is a detector buried in the ice of the South Pole. With no way of detecting the particle directly, they looked at how it was believed to interact with other neutrinos,

“Sterile means it doesn’t interact with matter itself, although it can dramatically interfere with the way conventional neutrinos do,” Halzen said. The researchers were hoping to see sterile neutrinos transforming into other types of neutrinos, which are known as flavors.

Standard Model still under questioning

The very fact that neutrinos can change flavors also presents a problem for the Standard Model. Over the course of the study scientists looked at atmospheric neutrinos that are created when cosmic rays hit particles in the Earth’s upper atmosphere.

It is thought to be more likely that neutrinos transform into sterile neutrinos after passing through dense matter. As a result scientists focused their efforts on the transformation of neutrinos that passed through the Earth’s core before hitting IceCube.

“What we’re looking for are neutrinos that are on the trajectory that pass through the core to disappear,” Conrad says.

Researchers looked at two data sets, each containing a year’s worth of data and approximately 100,00 neutrino events. However they did not see any evidence of the sterile neutrino.

“We did not find sterile neutrinos. However, we can’t rule them out completely,” Ben Jones, postdoctoral researcher at the University of Texas at Arlington says in the video. “What we can say is that if the anomalies 20 or 30 years ago were caused by sterile neutrinos, we would have expected to see a signal in our detector, and we didn’t see one.”

Halzen says that if the team had found concrete evidence of sterile neutrinos, it could have given them a clue about why the particles have such a small mass, or any mass at all.