November 18, 2011
New Tests Confirm Neutrinos Are Still Faster Than Light
Scientists who believed to have found in September that certain neutrinos travel faster than light have ruled out a potential source of error in their measurements after completing a second round of tests, further fracturing Einstein´s theory of relativity.
The team´s results, posted on the ArXiv preprint server this morning, confirmed their earlier measurements that neutrinos, sent through the ground from CERN -- on the Swiss-French border -- to the Gran Sasso lab in Italy 450 miles away, seemed to travel faster than the speed of light.
Scientist at the Italian Institute for Nuclear Physics (INFN) said in a statement that their new tests aimed to exclude one potential systematic effect that may have affected the original measurement.
“A measurement so delicate and carrying a profound implication on physics requires an extraordinary level of scrutiny,” Fernando Ferroni, president of the INFN, told Reuters. “The positive outcome of the test makes us more confident in the result, although a final word can only be said by analogous measurements performed elsewhere in the world.”
The first finding, back in September, from an international team of scientists shook the scientific community. Those findings came after scientists recorded 15,000 neutrino beams traveling from CERN to Gran Sasso in Rome.
Physicists working on the experiment -- called OPERA (Oscillation Project with Emulsion-tracking Apparatus) -- said they spent many months going over their findings checking for anything that could have produced a misreading before publishing their results. They had to be sure, because what they would publish could prove that Einstein was wrong when he made his theory that nothing could travel faster than the speed of light.
Matt Strassler, a theoretical physicist at Rutgers University, wrote about the latest experiment in his blog, stating that the shorter pulses of neutrinos being sent from CERN to Gran Sasso would remove the need to measure the shape and duration of the beam. “It´s like sending a series of loud and isolated clicks instead of a long blast on a horn.”
“In the latter case you have to figure out exactly when the horn starts and stops, but in the former you just hear each click and then it´s already over. In other words, with the short pulses you don´t need to know the pulse shape, just the pulse time,” he said.
“And you also don´t need to measure thousands of neutrinos in order to reproduce the pulse shape, getting the leading and trailing edges just right; you just need a small number — maybe even as few as 10 or so — to check the timing of just those few pulses for which a neutrino makes a splash in Opera,” Strassler added.
The Italian scientists working on the second set of experiments, said one potential source of error in the first results was that the pulses of neutrinos were relatively long at around 10 microseconds each, so measuring their exact arrival time could have had large errors.
To account for that potential source of error, the beams sent by CERN in the second round of experiments were shortened by about 3 nanoseconds, with large gaps of 524 nanoseconds between each firing, giving scientists at Gran Sasso more ease in timing their arrival more accurately.
“In this way, compared to the previous measurement, the neutrinos bunches are narrower and more spaced from each other,” the team of scientists said. “This permits to make a more accurate measure of their velocity at the price of a much lower beam intensity.”
However, this second experiment is not a full confirmation that the neutrinos are in fact faster than the speed of light, said Jacques Martino, director of the French National Institute of Nuclear and Particle Physics, who worked on the second experiment.
“The search is not over,” he said in a statement. “There are more checks of systematics currently under discussion.”
Since the Opera team at Gran Sasso announced their results, physicists around the world have published scores of online papers trying to explain the strange finding as either the result of a trivial mistake or evidence for new physics.
Dr Carlo Contaldi of Imperial College London suggested that different gravitational effects at CERN and Gran Sasso could have affected the clocks used to measure the neutrinos. Others have come up with ideas about new physics that modify special relativity by taking the unexpected effects of higher dimensions into account.
Despite the latest result, the observed faster-than-light anomaly in the neutrinos´ speed from CERN to Gran Sasso needed further scrutiny and independent tests before it could be refuted or confirmed definitively, said Dario Autiero of the French National Centre for Scientific Research (CNRS).
The Opera experiment will continue to take data with a new Muon detector well into next year, to improve the accuracy of the results.
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