Neutrino Blog: Weak Booom!
Of the large amount of papers that are being put forward for debunking faster than light neutrinos one in particular caught my eye. On Thursday a paper by Andrew G. Cohen and Sheldon L. Glashow about faster than light neutrinos losing energy rapidly and not making the 730km at superluminal speed. This post pulls together a lot of threads and I link to previous posts in the text to provide the relevant background.
The fundamental forces, the rule book for they way the Nature interacts with itself, are communicated to the Universe via things called fields. A good visual example of a field is putting iron filings near a bar magnet - this is the electromagnetic force field made visible. Every particle with an electric charge, e.g. the electron, emits a similar electromagnetic field. These force fields move at the speed limit of the universe - the speed of light. If the speed of light is slowed down, as it is in water or glass, then it is not against the laws of Nature for charged particles to out run light. If this is the case then the charged particles produce flashes of light known as Cherenkov radiation which takes energy away from the particle until it’s speed is less than light in water (or some other medium). For more info on Cherenkov light please read this previous post.
Neutrinos are ghostly as I have said many times and interact rarely with the Universe. On the rare occasion they do interact it is via the weak nuclear force. Because the neutrino feels this weak force, Cohen and Glashow put forward the argument that neutrinos would lose energy by a similar process to Cherenkov radiation. Instead of a burst of light however you would get a burst of weak force. Particles of light, photons, are the force carriers of the electromagnetic force and are the things released in Cherenkov radiation. The Z0 weak force carrier is essentially just a heavy version of the photon and it is this that is released in the burst of weak force.
The weak force carriers can’t live out in the real world for too long, due their heavy size they are unstable. They quickly die and give birth to matter and anti-matter. When Z0 dies it can produce pairs of electron and antielectron (positron)(a). In this process the neutrino loses energy until it reaches a lower limit (terminal energy) of about 12.5GeV. The OPERA experiment has however seen neutrinos with energy above this - with average energy about 17.5GeV. Quoting the paper “…observation of neutrinos with energies in excess of 12.5 GeV cannot be reconciled with the claimed superluminal neutrino velocity measurement.”
(a) The Z0 can also produce neutrino-antineutrino pairs, but the energy constraint here is less marked. Neutrinos can also lose energy by emitting light as well through a complicated self interation of the other weak force carriers the W± but this process is also not too important for this discussion.