Archive for OPERA Detector

Neutrinos on Speed

Posted in The Universe and Stuff with tags , , , on September 23, 2011 by telescoper

The internet, twitterdom, blogosphere, and even the mainstream media are all alive today with wild speculations about a curious claim that neutrinos might travel faster than light.

If you’re interested in finding the source of this story, look at the arXiv paper here. I haven’t got time to go through the paper in detail, but I think it must be an instrumental artefact or some other sort of systematic error.

One major reason for doubting the veracity of the claim that neutrinos travel faster than light is provided by astronomical observations. Neutrinos produced by the explosion of Supernova SN1987a were detected when it went boom in 1987, approximately three hours before the visible light from SN 1987A reached the Earth.

The few hours delay between neutrinos and photons is explained by the fact that neutrino emission occurs when the core of the progenitor star collapses, whereas visible light is released only when a shock wave reaches the surface of the imploding object. Three different experiments detected (anti)neutrinos: Kamiokande II found 11 , IMB 8 and Baksan 5, in a burst lasting less than 13 seconds.

If the time delay reported by the OPERA detector over the distance between CERN and Gran Sasso were extrapolated to the distance between Earth and SN1987a then the neutrinos should have arrived not a few hours early, but a few years, and there would not have been coincident arrivals at the different detectors on Earth.

Do neutrinos go faster than light?
Some physicists think that they might.
In the cold light of day,
I am sorry to say,
The story is probably shite

UPDATE: Now that I’ve read the paper let me point out that the OPERA result is essentially

δv/c = (2.48 ± 0.28(stat) ± 0.30(syst)) × 10-5,

whereas the constraints from Supernova 1987a work out to be   δv/c < 2 × 10-9 for  neutrino energies of 10 MeV. See the comments below for discussion.

I’ll also mention at this point that the analysis done in the paper is entirely based on frequentist statistics. Somebody needs to do it properly.