OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso
OPERA results indicate that the neutrinos travel at a velocity 20 parts per million above the speed of light, nature's cosmic speed limit.
September 26, 2011
The OPERA experiment, which observes a neutrino beam from CERN in Geneva, Switzerland, to Italy’s INFN Gran Sasso Laboratory 450 miles (730 kilometers) away, presented new results indicating an anomaly in the speed of subatomic neutrinos.
The Oscillation Project with Emulsion-tRacking Apparatus (OPERA) is an experiment to test the phenomenon of neutrino oscillations. It exploits CERN Neutrinos to Gran Sasso (CNGS), a high-intensity and high-energy beam of muon neutrinos produced at the CERN Super Proton Synchrotron in Geneva, Switzerland, and pointing to the Laboratori Nazionali del Gran Sasso (LNGS) underground laboratory, 455 miles (730 kilometers) away at Gran Sasso in central Italy.
The OPERA result is based on the observation of over 15,000 neutrino events measured at Gran Sasso, and appears to indicate that the neutrinos travel at a velocity 20 parts per million above the speed of light, nature's cosmic speed limit. Given the potential far-reaching consequences of such a result, independent measurements are needed before the effect can either be refuted or firmly established. This is why the OPERA collaboration has decided to open the result to broader scrutiny.
The OPERA measurement is at odds with well-established laws of nature, though science frequently progresses by overthrowing the established paradigms. For this reason, many searches have been made for deviations from Einstein's theory of relativity, so far not finding any such evidence. The strong constraints arising from these observations make an interpretation of the OPERA measurement in terms of modification of Einstein's theory unlikely, and give further strong reason to seek new independent measurements.
"This result comes as a complete surprise," said OPERA spokesperson Antonio Ereditato from 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."
"When an experiment finds an apparently unbelievable result and can find no artifact of the measurement to account for it, it's normal procedure is to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing — it's good scientific practice," said Sergio Bertolucci from CERN. "If this measurement is confirmed, it might change our view of physics, but we need to be sure that there are no other, more mundane explanations. That will require independent measurements."
In order to perform this study, the OPERA Collaboration teamed up with experts in metrology from CERN and other institutions to perform a series of high-precision measurements of the distance between the source and the detector, and of the neutrinos' time of flight. The distance between the origin of the neutrino beam and OPERA was measured with an uncertainty of 8 inches (20 centimeters) over the 450-mile (730 km) travel path. The neutrinos' time of flight was determined with an accuracy of less than 10 nanoseconds by using sophisticated instruments, including advanced GPS systems and atomic clocks. The time response of all elements of the CNGS beam line and of the OPERA detector has also been measured with great precision.
"We have established synchronization between CERN and Gran Sasso that gives us nanosecond accuracy, and we've measured the distance between the two sites to 8 inches (20 cm)," said Dario Autiero from CNRS. "Although our measurements have low systematic uncertainty and high statistical accuracy, and we place great confidence in our results, we're looking forward to comparing them with those from other experiments."
"The potential impact on science is too large to draw immediate conclusions or attempt physics interpretations. My first reaction is that the neutrino is still surprising us with its mysteries," said Ereditato.
The OPERA experiment was inaugurated in 2006, with the main goal of studying the rare transformation (oscillation) of muon neutrinos into tau neutrinos. One first such event was observed in 2010, proving the unique ability of the experiment in the detection of the elusive signal of tau neutrinos.