martes, 11 de marzo de 2014

750km of solid rock: new long-baseline neutrino results

Neutrino physics is one of the fastest-developing areas of particle physics.

Two ‘long-baseline’ neutrino experiments, in the US and Japan, reported results last week

Neutrinos are peculiar particles.

They are very common, billions are passing through you all the time.

Perhaps it is fortunate then that they very rarely interact with matter, and therefore do you no harm as they pass through.

They rarely interact because, uniquely among all the fundamental particles we know of that make up the matter in the universe, they only experience two of the four fundamental forces.

The have mass and energy, so they feel the gravitational force, and they also feel the weak force (that is the one carried by W and Z bosons).

But they have no charge, so they are invisible to the electromagnetic force; and the strong nuclear force also ignores them.

One thing we know about neutrinos is that when they are produced, they are one of three definite types – an electron, muon or tau type.

These types are known as flavours.

Flavour is just a label for the type of particle they can produce when they interact.

But a weird thing, which we also know, is that though there are neutrinos of three different flavours, and neutrinos of three different masses, the correspondence between the masses and the flavours is not straightforward.

The mixing between them is described by a matrix , with four different parameters that characterise how the mixing happens – basically what proportions of one kind of neutrino make up another.

(These cosmic rays produce many different kinds of particle, including neutrinos.)

Once you have built a neutrino detector (they are very big and very sensitive) you will most likely try to use any neutrinos you can, wherever they come from.

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