[Vision2020] Flaws found in faster-than-light neutrino measurement

[Ted Moffett]

Flaws found in faster-than-light neutrino measurement
http://www.nature.com/news/flaws-found-in-faster-than-light-neutrino-measurement-1.10099

Two possible sources of error uncovered.

   - Eugenie Samuel
Reich<http://www.nature.com/news/flaws-found-in-faster-than-light-neutrino-measurement-1.10099#auth-1>

22 February 2012

The OPERA collaboration, which made headlines in September with the
revolutionary claim that it had clocked neutrinos travelling faster than
the speed of light, has identified two possible sources of error in its
experiment. If true, its initial result would have violated Einstein’s
special theory of relativity, a cornerstone of modern
physics<http://www.nature.com/news/2011/110922/full/news.2011.554.html>
.

OPERA had collected data suggesting that neutrinos generated at CERN near
Geneva in Switzerland and sent 730 kilometres to its detector at Gran Sasso
National Laboratory in Italy were arriving 60 nanoseconds faster than a
light beam would take to travel the same distance. Many physicists were
sceptical, but the measurement seemed to have been done carefully and
reached a statistically significant level.

But according to a statement OPERA began circulating today, two possible
problems have now been found with its set-up. As many physicists had
speculated might be the case, both are related to the experiment’s
pioneering use of Global Positioning System (GPS) signals to synchronize
atomic clocks at each end of its neutrino beam. First, the passage of time
on the clocks between the arrival of the synchronizing signal has to be
interpolated and OPERA now says this may not have been done correctly.
Second, there was a possible faulty connection between the GPS signal and
the OPERA master clock.

An anonymously sourced account on *Science Insider* today broke the news
that OPERA may have made a
mistake<http://news.sciencemag.org/scienceinsider/2012/02/breaking-news-error-undoes-faster.html>.
That report says the faulty connection can account exactly for the
60-nanosecond effect. OPERA’s official statement stops short of that,
saying instead that its two possible sources of error point in opposite
directions and it is still working things out. Its statement reads in full:

“The OPERA Collaboration, by continuing its campaign of verifications on
the neutrino velocity measurement, has identified two issues that could
significantly affect the reported result. The first one is linked to the
oscillator used to produce the events time-stamps in between the GPS
synchronizations. The second point is related to the connection of the
optical fiber bringing the external GPS signal to the OPERA master clock.

“These two issues can modify the neutrino time of flight in opposite
directions. While continuing our investigations, in order to unambiguously
quantify the effect on the observed result, the Collaboration is looking
forward to performing a new measurement of the neutrino velocity as soon as
a new bunched beam will be available in 2012. An extensive report on the
above mentioned verifications and results will be shortly made available to
the scientific committees and agencies.”

Caren Hagner, a member of OPERA at the University of Hamburg in Germany,
says: “For the moment the collaboration decided not to make a quantitative
statement, because we have to recheck and discuss the findings more
thoroughly.”

At Fermilab in Batavia, Illinois, members of the MINOS collaboration (Main
Injector Neutrino Oscillation Search) continue to try to make their own
independent measurement of the speed of neutrinos, with initial results
expected later this year.

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Vision2020 Post: Ted Moffett
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