Neutrinos Faster Than Light?
Measurement of the neutrino velocity with the OPERA detector in the CNGS beam November 17, 2011
(T. Adam et al. Online. Available at: http://inspirehep.net/record/928153/files/arXiv:1109.4897.pdf?version=2)
Abstract: “The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos. The measurement is based on high statistics data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (57.8 ± 7.8 (stat.) (sys.)) ns was measured. This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c = (2.37 ± 0.32 (stat.) (sys.)) ×10-5. The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 μs long extractions, was confirmed by a test performed using a beam with a short-bunch time-structure allowing to measure the neutrino time of flight at the single interaction level.”
Nature Newsblog November 18, 2011
Neutrino experiment affirms faster-than-light claim
“It is a remarkable confirmation of a stunning result; but most physicists remain skeptical. That seems the most probable outcome of a release of new data expected on 17 November from researchers with the Italian OPERA collaboration, who say they have confirmed their controversial finding that flighty subatomic neutrinos can travel faster than light. ‘It’s slightly better than the previous result’, says OPERA’s physics coordinator Dario Autiero of the Institut de Physique Nucleaire de Lyon in France . . . . He adds that most of the members of the collaboration who declined to sign the original paper because they wanted more time to check the result have now come on board. . . . One set of concerns centered on the relatively long timescale – 10.5 microseconds, or 10.5 millionths of a second – of the proton pulses produced at CERN that result in the neutrino pulses OPERA detects. . . . In October OPERA therefore asked CERN to generate shorter proton pulses lasting just 3 nanoseconds. They have now recorded 20 events in the new data run and say that they have reached a similar level of statistical significance to the first time around, with the neutrinos again reaching Gran Sasso 60 nanoseconds faster than a light beam would do. OPERA expects the new result to rule out uncertainties due to the long timescale of the proton pulses. But concerns about the experiment’s use of the Global Positioning System to synchronize clocks at each end of the neutrino beam are unlikely to be as easily allayed. The use of GPS is novel in the field of high energy and particle physics and the same system was used for both the original experiment and the new run. . . . For most physicists outside the collaboration, however, the key test will be replication by an independent experiment. The one best placed to independently confirm or refute OPERA’s result is MINOS (the Main Injector Neutrino Oscillation Search) at Fermilab in Batavia, Illinois. In response to the latest OPERA result, MINOS issued a statement saying it is upgrading its timing system to match OPERA's precision and might have preliminary results obtained using the existing system that are relevant to assessing OPERA's results as soon as early 2012.”
Science February 24, 2012
“The CERN particle physics laboratory in Geneva has confirmed Wednesday's report that a loose fiber-optic cable may be behind measurements that seemed to show neutrinos outpacing the speed of light. But the lab also says another glitch could have caused the experiment to underestimate the particles' speed.
“In a statement based on an earlier press release from the OPERA collaboration, CERN said two possible ‘effects’ may have influenced the anomalous measurements. One of them, due to a possible faulty connection between the fiber-optic cable bringing the GPS signals to OPERA and the detector's master clock, would have caused the experiment to underestimate the neutrinos’ flight time, as described in the original story. The other effect concerns an oscillator, part of OPERA's particle detector that gives its readings time stamps synchronized to GPS signals. Researchers think correcting for an error in this device would actually increase the anomaly in neutrino velocity, making the particles even speedier than the earlier measurements seemed to show.
“CERN's statement says OPERA scientists are studying the ‘potential extent of these two effects’ but doesn't indicate which source of error (if either) is likely to outweigh the other. However, Lucia Votano, director of the Gran Sasso laboratory, says the ‘main suspicion’ focuses on the optical-fiber connection. She adds that OPERA researchers deserve credit for ‘having tenaciously followed this particular evidence via checks completed in the last few days’.
“The two effects will get a new round of tests in May, when the two labs are scheduled to make velocity measurements with short-pulsed beams designed to give readings much more precise than scientists have achieved so far.”
BBC News March 16, 2012
Neutrinos clocked at light-speed in new Icarus test
“An experiment to repeat a test of the speed of subatomic particles known as neutrinos has found that they do not travel faster than light. . . . In November, the Icarus group showed in a paper posted on the online server Arxiv that the neutrinos displayed no such behaviour. . . they have now supplemented that indirect result with a test just like that carried out by the Opera team. Since their November result, the Icarus team have adjusted their experiment to do a speed measurement. What was missing was information from Cern about the departure time of the neutrinos, which the team recently received to complete their analysis. The result: they find that the neutrinos do travel at the same speed as light, within a small error range. ‘We are completely compatible with the speed of light that we learn at school,’ said Sandro Centro, co-spokesman for the Icarus collaboration. . . . Four different experiments at Italy's Gran Sasso lab make use of the same beam of neutrinos from Cern. Later this month, they will all be undertaking independent measurements to finally put an end to speculation about neutrino speeds. The Minos experiment in the US and the T2K experiment in Japan may also weigh in on the matter in due course — if any doubt is left about the neutrinos' ability to beat the universal speed limit.”
Phys.Org June 8, 2012
Einstein was right, neutrino researchers admit
“Researchers updated the science community on Friday at the International Conference on Neutrino Physics and Astrophysics, being held in Japan's ancient capital of Kyoto.
“‘The previous data taken up to 2011 with the neutrino beam from CERN to Gran Sasso were revised taking into account understood instrumental effects’, the team said.
“‘A coherent picture has emerged with both previous and new data pointing to a neutrino velocity consistent with the speed of light’.”