A joint Fermilab/SLAC publication

OPERA experiment sees neutrinos seem to beat speed of light


The OPERA experiment began in 2006 with the main goal of studying neutrino oscillation. Image courtesy of OPERA

The OPERA neutrino experiment announced today the kind of result that keeps a physicist up at night.

Scientists revealed that they have observed subatomic particles seeming to travel faster than the speed of light.

Leaders of the collaboration will share OPERA data with the world today at 9 a.m. CDT during a seminar to be broadcast live on the web. They have already posted the relevant paper online.

The OPERA experiment's study of more than 15,000 neutrino events over the course of three years indicated that the particles reached a velocity 20 parts per million above light speed.

If neutrinos really are breaking the cosmic speed limit, a revolution is at hand in the field of particle physics. Einstein’s law of special relativity as we understand it and a century of experiment tell scientists such a result is impossible.

So, to them, the next step is clear: They will try their best to prove it wrong.

“This result comes as a complete surprise,” said OPERA spokesperson Antonio Ereditato of the University of Bern. “After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement. While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation.”

Neutrinos are some of the most mysterious particles studied today. They rarely interact with other matter, so they have the ability to slip quietly through space and entire planets as if they weren’t there. The only way scientists can detect enough of these subatomic ghosts to study their properties is to aim an intense beam of them at a large target.

OPERA is a long-baseline neutrino experiment, meaning that its detector sits far from its neutrino source. For the OPERA experiment, particles stream from their origins at CERN to Gran Sasso, Italy, more than 450 miles away. Long-baseline experiments allow scientists to study a strange trait of the particles. Neutrinos come in three types, called flavors. As they travel, neutrinos oscillate from one flavor to another.

These experiments can also take precision measurements such as the one announced today. Two other long-baseline neutrino experiments, one in the United States and the other in Japan, could double-check OPERA’s results. The MINOS experiment sends a beam of neutrinos from Fermi National Accelerator Laboratory into a 6,000-ton detector in a former iron mine about 450 miles away in northern Minnesota. The T2K experiment studies neutrinos that travel more than 180 miles through Japan from Tokai to Kamioka.

Previous results from the MINOS experiment do not contradict OPERA’s findings, but they are less certain. Scientists on the MINOS collaboration plan to improve the accuracy of their measurement with upgrades already underway.

Members of MINOS and T2K, along with scientists from around the world, will scrutinize the OPERA measurement, looking for fatal flaws. Still other scientists will prepare for another possibility: What if the result is right? “In the upcoming weeks, we’ll see a flurry of papers come out with different interpretations of this,” said CERN theoretical physicist John Ellis.

Not all theorists will jump in. Many will wait for confirmation by other experiments before taking on the problem of how to square superluminal neutrinos with the rest of physics.

But those that offer their interpretations will guide experimentalists by giving them new parameters to test, Ellis said. “It’s good to produce a bunch of reactions and see which way nature decides to go.”

Read updates:
Scientists still seek explanation for faster-than-light neutrino result
Faster-than-light neutrino result withstands new test

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