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Two new subatomic particles discovered at CERN

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Re: Two new subatomic particles discovered at CERN

#31

Post by mkartic »

cozzyd wrote: post #3

In case people are wondering about the impact of this, it's not very interesting (to non particle physcists) unless something unexpected about these particles is found later, as these particles were predicted by the Standard Model. The exact mass splittings, of course, are useful to validate (and further improve) theoretical models of QCD. What I find more interesting is that LHCb is licensing their eprint as CC-BY-4…

Are the particles found first and retrofitted into the Standard Model? Or does the model act as a map of sorts by telling us where to look? If latter, does that mean we're not looking for particles outside of the standard model?

Re: Two new subatomic particles discovered at CERN

#33

Post by Already__Taken »

mkartic wrote: post #31
cozzyd wrote: post #3

In case people are wondering about the impact of this, it's not very interesting (to non particle physcists) unless something unexpected about these particles is found later, as these particles were predicted by the Standard Model. The exact mass splittings, of course, are useful to validate (and further improve) theoretical models of QCD. What I find more interesting is that LHCb is licensing their eprint as CC-BY-4…

Are the particles found first and retrofitted into the Standard Model? Or does the model act as a map of sorts by telling us where to look? If latter, does that mean we're not looking for particles outside of the standard model?

/Not a physicist in any way but;

The approach seems to be we observe a lot of behaviour, then build up models to explain that behaviour. If particles need to be made up to balance an equation then they get made up.

You project that model into some scenario to say "If this model is right, the following ... will happen" and observe. If you're right then work goes on for further evaluate "What about this scenario" and finally a big machine gets built to directly work out, from all that's prior, if a particle that needs X,Y,Z properties really does exist is should be seen in the measurements that are supposed create it.

So to answer your question; Both?

E.g You could take the model, put it in a computer. Simulate what the LHC does and look at that graph of kind of particles it makes. Then you build the LHC, actually smash some things together. Same graph?

Re: Two new subatomic particles discovered at CERN

#34

Post by jontas »

danbruc wrote: post #10

Why does nobody include the particle name in the heading? Supersymmetry?!? Click. Nope, some pseudo particle or a bunch of quarks.

From one of the articles linked in in the HN comments [0]:

> The particles, known as the Xi_b'- and Xi_b-, were predicted to exist by the quark model but had never been seen before. A related particle, the Xi_b0, was found by the CMS experiment at CERN in 2012. The LHCb collaboration submitted a paper reporting the finding to Physical Review Letters.*

0: http://home.web.cern.ch/about/updates/2014/11/lhcb-observes-...

* some of the formatting of the particle names got borked by the HN comment system limitations--I tried using tags but they don't appear to work. The correct spelling/representation of the particle names can be found in [0]

Re: Two new subatomic particles discovered at CERN

#35

Post by evanb »

pbhjpbhj wrote: post #13
cozzyd wrote: post #3

In case people are wondering about the impact of this, it's not very interesting (to non particle physcists) unless something unexpected about these particles is found later, as these particles were predicted by the Standard Model. The exact mass splittings, of course, are useful to validate (and further improve) theoretical models of QCD. What I find more interesting is that LHCb is licensing their eprint as CC-BY-4…

PRL = Physics Review Letters, paper in question: http://arxiv.org/pdf/1411.4849v1.pdf . Of course the PRL version will not be CC-BY and citations that reference it will likely not find the CC-BY version. I wonder if it will matter in any material way to PRL - no more so at least than the situation where papers are available direct from a repository on an author's personal webpage. The pre-print already being on Arxiv…

Physicists often DO add the arxiv reference to the published version in citations. Moreover, people know to search the arXiv, so I wouldn't discount the possibility that people find this version.

Re: Two new subatomic particles discovered at CERN

#36

Post by evanb »

mkartic wrote: post #31
cozzyd wrote: post #3

In case people are wondering about the impact of this, it's not very interesting (to non particle physcists) unless something unexpected about these particles is found later, as these particles were predicted by the Standard Model. The exact mass splittings, of course, are useful to validate (and further improve) theoretical models of QCD. What I find more interesting is that LHCb is licensing their eprint as CC-BY-4…

Are the particles found first and retrofitted into the Standard Model? Or does the model act as a map of sorts by telling us where to look? If latter, does that mean we're not looking for particles outside of the standard model?

The Standard Model is a list of fundamental particles (electron, muon, tau, their corresponding neutrinos, and 6 flavors of quarks: up, down, strange, charm, top, and bottom) as well as their interactions (electroweak force & strong nuclear force). The input to the SM are around 20 numbers controlling the masses of these particles and the strengths of the interactions, as well as a few Higgs parameters. After that, everything is fixed, so that the SM makes definite predictions about where to look to find new baryons and mesons (things made out of quarks). It's not quite so simple as "add up the masses of the constituent quarks" because the strong interactions translate into mass (essentially via E=mc^2)---exactly how big an effect the strong force has requires calculation.

So the SM is a map telling you where to look, but a very sneaky kind of map. In the sector where the strong force matters, it's as if someone encrypted a map, and for every new destination you want to find out about, you have to expend computational resources to decrypt it. In principle, you have all the information, but in practice it is hard to extract predictions from the theory. That is a very peculiar situation for scientists to be in: to have a definite, precise theory, and the opportunity to do experiments, but to struggle to compare the two!

Anyway, these particles are predicted by the SM, where "predicted by" means after expending a lot of computation to understand the strong dynamics one finds out that these particles (which are quarks held together by gluons) should be there.

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