Giving this its own thread, now.

There has been interesting news from CERN yesterday about the data they have taken with increased collision energy this year. It has transpired that the two largest experiments  fed by the LHC beam, ATLAS and CMS, both see an excess of events with two photons at roughly the same energy, 750 GeV.  This is what the ATLAS data look like



Just for comparison, this is what the Higgs boson looked like in its two photon signature at some point (now the statistics is better)



Each experimental deviation by itself would not get  physicists to raise an eyebrow, because if you look in enough different places in the data, such fluctuations are likely to occur, even expected. But to see compatible excesses at the same energy in both experiments, which are statistically completely independent, that is something worth having a closer look at. Should one get cautiously excited? I don't know, seemingly astonishing signals have gone away in the past when more data was collected. If it is really a new particle, it is bound to be something special - another Boson. If it has spin 2, it is groundbreaking, because we will either have found some unexpected form of quantum gravity and maybe new dimensions of space, or a composite particle of a composition hitherto unknown to science, which would open the door to a phantastic new world of discovery. If it  has spin 0, it might be a bigger brother of the Higgs boson, which could revolutionize our understanding of the origin of the Higgs boson itself. One of the big puzzles in fundamental physics is how the Higgs boson - theoretically - manages to be so light when it should be pushed to much higher masses by its interactions with virtual particles. A second scalar boson is bound to shed light on this issue.

A new particle is always a potential gateway to an entirely new "world". For example, while we have not been successful to detect dark matter until now, such a new boson - while it cannot form dark matter itself because it decays - might be the key to finally connect to this dark side of the universe: in several proposed theory hypotheses, such a boson is the link between the known particles we are made of, and a "dark" sector.

Probably only the enhanced experimental statistics of the next LHC run in 2016 will tell, but people will now comb through the existing data whether one can find traces of such a new particle in different particle constellations that have been overlooked because one didn't specifically look for such a signature.

In any case, such a discovery would be the first discovery of a new particle in 40 years that was not already expected theoretically and via indirect observations like the Higgs - a completely new chapter in physics - if it is true...

Kevin (from virtual sims inc), please make some coding changes to the sandbox boundary algorithm for sim:EARTH, they're onto you...

You know when Peter bangs his knee and sits on the ground holding it, going "(inhale through teeth) ahhhhh (inhale through teeth) ahhhhhh". I'm doing that with my brain.

Who is Peter?

He's the Family Guy.

Oh, I see! I've never watched FG.

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.

(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.

You know when Peter...

Haha No, this helps. I was always told not to think of spin as I normally would, and here you've sort of told me to do exactly that.

(December 16, 2015 at 10:34 am)Exian Wrote: You know when Peter...

Haha No, this helps. I was always told not to think of spin as I normally would, and here you've sort of told me to do exactly that.

The problem is that there is afaik no alternative way to think about spin in terms of anything familiar that would more accurately convey what it is. So "behaves as if it were rotating, even though it isn't" is as good as it gets... and it's honestly not such a bad picture at all physics wise.