Tuesday, October 18, 2011

A Challenge To The OPERA conclusion on FTL Neutrinos

Tommaso Dorigo's blog is touting a new paper from the ICARUS experiment on the energy profile of neutrinos from CERN as refutation of the OPERA conclusion that it has observed superluminal neutrinos. (The Cohen and Glashow paper he cites has essentially the same problems.)

While it is a worthwhile paper, I'm not convinced that it proves what he claims that it does. True, very high speed neutrinos don't behave like hypothetical tachyons described in these theoretical papers describing them that are not supported by anything but generalizations of equations that also essentially assume that nothing can go faster than the speed of light.

Instead, ICARUS shows that neutrinos behave, relative to each other, just like we would expect ordinary Lorentz invariant fermions to behave. They used their data to compare the energy of neutrinos detected to those interacting with W bosons and Z bosons according to the Standard Model, and the data fit.

But, what the ICARUS paper doesn't prove is the absolute speed of the neutrinos. Neutrinos certainly act like Lorentz invariant particles relative to some speed limit "c", but whether that speed limit is the speed of light measured in other experiments conducted with photons, or is some other slightly different speed limit (by a factor of 10^-5 in over 732 km in the OPERA experiment), ICARUS can't tell us. It could be that there is a systemic error in the conventionally accepted measured value of "c" based on photon measurements, for example, that isn't present in direct measurements of neutrinos speed.

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