> The standard model makes no claim as to how many particles there can be
Nope, it does. That's kind of the whole point of it.
> what their masses should be
True, these are free parameters (except the massless bosons)
> what spin they should have
It does. Fundamental fermions have to be spin-1/2, gauge bosons spin-1 and the Higgs spin-0.
> A new particle doesn't necessarily violate the standard model in the same way that discovering a new element wouldn't necessarily violate the periodic table.
Depends if you mean a new fundamental particle or a new hadron. Discovering a new hadron is akin to adding a new element to the periodic table. Discovering a new fundamental particle means the Standard Model has to be extended or otherwise rewritten.
I was thinking of the Standard Model as more of a moving target that incorporates everything we know about the fundamental particles and their forces. I thought the model started with a smaller number of particles [photon, electron, neutrino, muon neutrino, up quark, down quark, strange quark, gluon] and was expanded over time [higgs in 64, w/z bosons in 68, charm in 70, top/bottom in 73]. After further investigation it looks like no one actually called it the "Standard Model" until all of the 17 particles known today were included, so technically there have been no new particles added to the "Standard Model"
I think considering the Standard Model a moving target is still reasonable since if a new fundamental particle were to be discovered tomorrow, we would very likely just add it to the Standard Model and still call the new version the "Standard Model". However, I also realize now that treating it in this way is probably not appropriate given the context of mojoe's original question. I would edit my original comment to retract what I've said, but it seems I took too long to recognize my mistake and it will be forever immortalized in hacker news history :(
> I think considering the Standard Model a moving target is still reasonable
IMO no. The standard model isn't just a table full of particles, it's much more. One core part is is the description of how these particles behave, and the lagrangian. These could change much more drastically if a new particle turned up. This is because the particles in the standard model are intimately tied with underlying representation groups, which can't accomodate another particle. It's possible folks would still call it the "Standard Model", but I suspect such a drastic change would get a new name.
No, it was there from the beginning.
> The standard model makes no claim as to how many particles there can be
Nope, it does. That's kind of the whole point of it.
> what their masses should be
True, these are free parameters (except the massless bosons)
> what spin they should have
It does. Fundamental fermions have to be spin-1/2, gauge bosons spin-1 and the Higgs spin-0.
> A new particle doesn't necessarily violate the standard model in the same way that discovering a new element wouldn't necessarily violate the periodic table.
Depends if you mean a new fundamental particle or a new hadron. Discovering a new hadron is akin to adding a new element to the periodic table. Discovering a new fundamental particle means the Standard Model has to be extended or otherwise rewritten.