RE: A new Boson?
December 16, 2015 at 10:20 am
(This post was last modified: December 16, 2015 at 10:28 am by Alex K.)
(December 16, 2015 at 10:09 am)Exian Wrote: Seriously though, this is pretty exciting (I think). But it's been a long time since I've lent myself to this material. If I knew what the hell spin meant in this context and if I could wrap my head around some other dimension (direction?) of space, I'd get more excited.
Oh all right. So you are probably somewhat vaguely familiar with the concept of angular momentum, right? It's basically the rotational momentum a rotating object has. It is proportional to the torque you have to apply for a given amount of time in order to get it going round at that speed. Ok!
Now, it turns out that, maybe surprisingly, many particles have such an angular momentum built in even if they are at rest, a bit as if they were little rotating balls, except that they are not rotating in any meaningful sense. This built-in angular momentum is called spin.
A particle (or any object for that matter) cannot have arbitrary continuous values of angular momentum because of the quantum gejiggers, but only half integer multiples of Plancks constant (just accept that for now, it is not easy to explain at all why that is - it comes out from the maths). It is therefore customary to count the intrinsic angular momentum of particles in multiples of the smallest possible value: 0, 1/2, 1, 3/2, 2...
The ones with 0,1,2... are called Bosons, the ones with 1/2, 3/2 ... are called Fermions.
Now, all the elementary particles we know have 0 (the Higgs), 1/2 (the Quarks, Leptons and Neutrinos) or 1 (the Photon, Gluons, W and Z bosons). We know particles with 3/2 and 2, but they are all composites of quarks, and the extra spin comes from stuff actually going in a circle inside those particles, and/or the spin of several elementary particles adding up. But we don't know any elementary particles with 3/2 or 2.
What makes Spin 2 exciting is that this is the spin carried by one particular hypothetical particle, the Graviton which is thought to be the elementary quantum of gravitational waves. So if there is talk of a spin 2 particle, people will immediately hope that this has somehow something to do with Gravity.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
