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| Neutrino experiment repeat at Cern finds same result | Neutrino experiment repeat at Cern finds same result |
| (40 minutes later) | |
| By Jason Palmer Science and technology reporter, BBC News | By Jason Palmer Science and technology reporter, BBC News |
| The team which found that neutrinos may travel faster than light has carried out an improved version of their experiment - and confirmed the result. | |
| If confirmed by other experiments, the find could undermine one of the basic principles of modern physics. | If confirmed by other experiments, the find could undermine one of the basic principles of modern physics. |
| Critics of the first report in September had said that the long bunches of neutrinos (tiny particles) used could introduce an error into the test. | |
| The new work used much shorter bunches. | |
| It has been href="http://arxiv.org/abs/1109.4897v2" >posted to the Arxiv repository and submitted to the Journal of High Energy Physics, but has not yet been reviewed by the scientific community. | |
| The experiments have been carried out by the Opera collaboration - short for Oscillation Project with Emulsion (T)racking Apparatus. | |
| It hinges on sending bunches of neutrinos created at the Cern facility (actually produced as decays within a long bunch of protons produced at Cern) through 730km (454 miles) of rock to a giant detector at the Gran Sasso laboratory in Italy. | |
| The initial series of experiments, comprising 15,000 separate measurements spread out over three years, found that the neutrinos arrived 60 billionths of a second faster than light would have, travelling unimpeded over the same distance. | |
| The idea that nothing can exceed the speed of light in a vacuum forms a cornerstone in physics - first laid out by James Clerk Maxwell and later incorporated into Albert Einstein's theory of special relativity. | The idea that nothing can exceed the speed of light in a vacuum forms a cornerstone in physics - first laid out by James Clerk Maxwell and later incorporated into Albert Einstein's theory of special relativity. |
| Timing is everything | Timing is everything |
| Initial analysis of the work by the wider scientific community argued that the relatively long-lasting bunches of neutrinos could introduce a significant error into the measurement. | Initial analysis of the work by the wider scientific community argued that the relatively long-lasting bunches of neutrinos could introduce a significant error into the measurement. |
| Those bunches lasted 10 millionths of a second - 160 times longer than the discrepancy the team initially reported in the neutrinos' travel time. | Those bunches lasted 10 millionths of a second - 160 times longer than the discrepancy the team initially reported in the neutrinos' travel time. |
| To address that, scientists at Cern adjusted the way in which the proton beams were produced, resulting in bunches just three billionths of a second long. | To address that, scientists at Cern adjusted the way in which the proton beams were produced, resulting in bunches just three billionths of a second long. |
| When the Opera team ran the improved experiment 20 times, they found almost exactly the same result. | When the Opera team ran the improved experiment 20 times, they found almost exactly the same result. |
| "This is reinforcing the previous finding and ruling out some possible systematic errors which could have in principle been affecting it," said Antonio Ereditato of the Opera collaboration. | "This is reinforcing the previous finding and ruling out some possible systematic errors which could have in principle been affecting it," said Antonio Ereditato of the Opera collaboration. |
| "We didn't think they were, and now we have the proof," he told BBC News. "This is reassuring that it's not the end of the story." | "We didn't think they were, and now we have the proof," he told BBC News. "This is reassuring that it's not the end of the story." |
| The first announcement of evidently faster-than-light neutrinos caused a stir worldwide; the Opera collaboration is very aware of its implications if eventually proved correct. | |
| The error in the length of the bunches, however, is just the largest among several potential sources of uncertainty in the measurement, which must all now be addressed in turn; these mostly centre on the precise departure and arrival times of the bunches. | The error in the length of the bunches, however, is just the largest among several potential sources of uncertainty in the measurement, which must all now be addressed in turn; these mostly centre on the precise departure and arrival times of the bunches. |
| "So far no arguments have been put forward that rule out our effect," Dr Ereditato said. | "So far no arguments have been put forward that rule out our effect," Dr Ereditato said. |
| "This additional test we made is confirming our original finding, but still we have to be very prudent, still we have to look forward to independent confirmation. But this is a positive result." | "This additional test we made is confirming our original finding, but still we have to be very prudent, still we have to look forward to independent confirmation. But this is a positive result." |
| That confirmation may be much longer in coming, as only a few facilities worldwide have the detectors needed to catch the notoriously flighty neutrinos - which interact with matter so rarely as to have earned the nickname "ghost particles". | That confirmation may be much longer in coming, as only a few facilities worldwide have the detectors needed to catch the notoriously flighty neutrinos - which interact with matter so rarely as to have earned the nickname "ghost particles". |
| Next year, teams working on two other experiments at Gran Sasso experiments - Borexino and Icarus - will begin independent cross-checks of Opera's results. | Next year, teams working on two other experiments at Gran Sasso experiments - Borexino and Icarus - will begin independent cross-checks of Opera's results. |
| The US Minos experiment and Japan's T2K experiment will also test the observations. It is likely to be several months before they report back. | The US Minos experiment and Japan's T2K experiment will also test the observations. It is likely to be several months before they report back. |