Neutrinos Speed Past Light, Maybe

Last week, the world’s biggest physics lab unveiled a shocking finding: that one type of subatomic particle was clocked going faster than the speed of light. If true, it could undercut Albert Einstein’s theory of relativity.

Since 1905 the C in Einstein’s famous equation E=MC2 has stood for the speed of light. Until now, that has always been a constant amount which can always be measured at 186,282.397 miles per second.

The new announcement coming from the European nuclear research facility CERN surprised a lot of scientists, including those who made the observations.

CERN Research Director Sergio Bertolucci says, “When an experiment finds an apparently unbelievable result and can find no artifact of the measurement to account for it, it’s normal procedure to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing, it’s good scientific practice.”

Antonio Ereditato of the University of Bern and a spokesman for the OPERA project says the result came as a complete surprise. But rather than just accepting such an unsual measurement, the team went to work, trying to find a reasonable explanation. He says, “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.”

In 2006 the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) project began with the goal of studying the rare transformation (oscillation) of muon neutrinos into tau neutrinos.

Neutrinos, like the ones above, have been detected travelling faster than light, say particle physicists. Photograph: Dan Mccoy /Corbis

To better understand this here are the basics on neutrinos.

Neutrinos are elementary subatomic particles. They are so small that they have almost no mass. They are still considered matter and therefore described as particles. Neutrinos are electrically neutral which means they can pass through matter, including people and the planet without leaving much of a trace. There are three flavors of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos.

Most of the 65 billion neutrinos that pass through every centimeter of the solar-facing side of Earth every second emanate from the sun, where they form as a result of radioactive decay interacting with atoms. On Earth, nuclear reactors can create neutrinos like those measured at CERN.

It took just 3 milliseconds for these particles to travel from Geneva, Switzerland to Gran Sasso, Italy, nearly 500 miles away.

Brian McLaughlin, Geek Dad, told Wired News, “In the experiment, neutrinos are generated at the Super Proton Synchrotron (SPS) particle accelerator at the CERN LHC complex in Geneva and further accelerated down a 1 km beam line toward the Gran Sasso National Laboratory in Italy. At Gran Sasso, a detector instrument called OPERA measures the neutrinos. The distance from CERN to Gran Sasso is 732 km straight through the Earth, traveling up to 11.4 km below the Earth’s surface. Remember, neutrinos don’t interact with matter so the Earth is invisible to the tiny particles.

The distance between the two systems is known to within 20 cm. Time is also measured with extreme precision utilizing GPS timing signals and a cesium atomic clock. The GPS used in timing also allows the team to track any small movements in the Earth itself. This even allowed consideration of the effect of the L’Aquila Earthquake that moved the OPERA detector 7 cm. Due to the nature of the experiment, the time is not calculated with a simple, stopwatch style, start to finish measurement. It instead relies on measurements and comparisons of probability distribution functions at the source and the detector. In other words, there is a lot of math involved. In addition to understanding the timing and position variations in the experiment, the physicists also took into account many other variables, such as day versus night and seasonal changes. The sensitivity of this experiment is roughly an order of magnitude better than previous experiments.”

In 2010, the OPERA team observed its first neutrino oscillation event, proving the unique ability of the experiment in the detection of the elusive signal of tau neutrinos.

And in studying the precise movement of these particles between CERN and the lab in Gran Sasso, the team noticed that the neutrinos were arriving faster than they calculated. It’s not a whole lot faster–just 60 nanoseconds ahead of schedule. But that means they were traveling faster than the speed of light.

Immediately the team thought there was a miscalculation somewhere so they went to work ruling out the possibility that a neutrino could travel faster than the speed of light. After validating their calculations they realized the magnitude of this observed measurement. With a clear margin of error of 10 nanoseconds, suddenly the 60 nanosecond difference became significant.

Scientists won’t know just how significant this is until they are able to confirm the measurement at a couple of separate labs. Already the Fermilab in Illinois and the T2K neutrino experiment in Japan (which was pushed offline after the big quake there this year) have volunteered to re-measure and replicate the experiment to confirm the neutrinos’ speed.

“I don’t want to call this a discovery. I want to say this is a measurement. It’s an intriguing measurement. It’s a precise measurement. And in order for this measurement to become a discovery we will need more work.”–Antonio Ereditato, OPERA team member at CERN