More neutrino news

February 23, 2012

We’ve been following ongoing developments in the allegedly-faster-than-light neutrinos story from CERN. Vince very kindly left a comment pointing out that there is fresh news today:

ScienceInsider […] said “sources familiar with the experiment” are now blaming the original result on a fibre optic cable connecting a GPS receiver to an electronic card in a computer. The GPS is one of the devices used in the measurement of the neutrino’s travel time. The cable connection appeared to have been loose, and tightening it shortened data travel times by 60 nanoseconds.

“Since this time is subtracted from the overall time of flight, it appears to explain the early arrival of the neutrinos,” the article said. “New data, however, will be needed to confirm this hypothesis.”

The original timing was off expectations by about 60 ns, so this might well resolve the issue. However, a CERN press release from earlier today reveals that the situation may be slightly more complicated:

The OPERA collaboration has informed its funding agencies and host laboratories that it has identified two possible effects that could have an influence on its neutrino timing measurement. These both require further tests with a short pulsed beam. If confirmed, one would increase the size of the measured effect, the other would diminish it. The first possible effect concerns an oscillator used to provide the time stamps for GPS synchronizations. It could have led to an overestimate of the neutrino’s time of flight. The second concerns the optical fibre connector that brings the external GPS signal to the OPERA master clock, which may not have been functioning correctly when the measurements were taken. If this is the case, it could have led to an underestimate of the time of flight of the neutrinos. The potential extent of these two effects is being studied by the OPERA collaboration. New measurements with short pulsed beams are scheduled for May.

So there are really two potential issues contributing to the timing problems, only one of which pushes the result in the right direction. Obviously we’ll have to wait until the experiments are done to know how it turns out. In the meantime we can sit around wondering why science journalists are only reporting on one of the two sources of error.

6 Responses to “More neutrino news”

  1. Vince Says:

    If an experiment that generates a lot of media buzz fails, I’m sure the journalists want the failure to be amusingly attributed to a bad cable connection, as though it were discovered by a PC tech support specialist over the phone.

  2. cburrell Says:

    Hah! There may be something to that.

  3. Mac Says:

    Yeah, if CERN had called me, I would have told them to check their cable connections before announcing any revolutionary test results. Also to make sure they didn’t have caps lock on.

  4. cburrell Says:

    There is actually an instructive lesson here about how difficult it is to do good experiments. There were, I expect, many thousands of cables involved in this measurement. A flaw in a single one could (apparently) produce the kind of anomalous result they found. If I were an experimentalist, this would make me shudder.

    This also highlights how important it is to repeat experiments at independent facilities. As particle physics experiments get bigger, that becomes more and more difficult to do. (This neutrino experiment is, by comparison, a pretty small operation, but it requires a beam of neutrinos, and that is rare.)

  5. Matthew Says:

    Not all journalists missed the two sources of error. For news from outside Canada, I always look to the BBC.

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