[wolfgke]

> Their discovery will help to address important unsolved questions about how hadrons are bound together by the strong interaction.

If the particles were already predicted by the standard model, what kind of unsolved questions are to address here, besides validating the predictions of the standard model even further? (serious question)

[inlineint]

The standard model provides a set of postulates that could be used for prediction of possible composite particles, their masses, and decay times.

However it is computationally infeasible to calculate them directly, without using various approximations. Physicists try to solve these problems numerically (see for example about the field called lattice QCD), but it is not always possible and leads to introducing various approximations that produce errors and other artifacts in the numerical predictions.

So the particles were allowed by the standard model, but we didn't know for sure their properties. So this provides way to verify already done numerical predictions (I don't really know were they be done for this exact particles or not) and give us data about exact properties of these particles.

One could possibly draw an analogy with (quantum) chemistry here.

[gus_massa]

I'm not sure about this particular one, but a general idea is that the properties you are measuring in a particle depends on a lot of virtual particles.

It's difficult to find an easy example. After some searches in Google I found this unrelated example: http://www.strings.ph.qmul.ac.uk/~bigdraw/feynman/slide3.htm...

It has 9 Feynman diagrams. If you look at the top left diagram, there is an electron that enters from the bottom right corner, then it emits a photon that go out thought the top left corner, then the electron goes out through the top left corner.

The following two diagrams show the case were the electron emits a second (and third) photon and reabsorbs it, so the second (and third) photons are not visible for the experimenter, they are virtual photons. These additional photons are only important because the change slight the properties of the electron.

In the next three diagrams the photon is so strong that it can spontaneously split in another electron and a positron. It looks like a loop/circle, because positrons are like electrons traveling backward in time. They are virtual electrons, and again they are not visible in the lab, they are only important to make a tiny correction to the result of the experiment.

The other three diagrams have two virtual electrons, than makes even smaller corrections.

And in addition of the virtual electrons, there can be virtual muons and tauons. They are like electrons but with more mass. So the probability of having one of them is smaller, so the correction is smaller. In this case, I think that the correction is so small that it's impossible to measure it.

And you can have another virtual particles, like virtual quarks and virtual W, anything that has a charge. Moreover you can have virtual unknown particles (with charge) because nature doesn't care if we know the particle yet or not. But they are heavier, so the correction is negligible.

If you change the experiment, and for example make a electron collide with a positron, then the calculations are very similar, but there is more energy laying around, and the corrections from heavy particles are more important, so this variation is more useful to discover new particles.

Back to your question ...

The new particles are composed by three quarks, but actually they are composed by a lot of gluons and virtual quarks and antiquarks. To do any calculations you have to include a lot of diagrams like in the figure linked above, and a lot more, many many more.

IIRC the calculation is so complex that it's not possible to compare the experimental results with theoretical calculations. Perhaps they have some heuristic to compare the results with the results of similar particles.

This was probably part of a bigger experiment that produces a lot of particles, and they are trying to classify them in families. And perhaps in the classifications they can spot some strange pattern that may provide a hit that there is a new elementary particle.

[dukwon]

Since QCD can't be calculated perturbatively at low energy, there are unsolved problems with how to get those predictions in the first place.

[binarymax]

Because a prediction is just an assumption (theory), and it can become a house of cards when basing future science on that assumption. Observation is proof, so future science can use that proof without worry.

[nonbel]

Can you clarify? In my mind

  "prediction" != "assumption" != "theory" 

and

  "observation" != "proof"

Basically I seem to disagree with everything you wrote.

[herpdorplarp]

By assuming validity of a theory you can make predictions. Observations provide evidence in support of this.

[iamconfused]

A theory comes later. You start off with a hypothesis. You don't make any assumptions of validity.

[iamconfused]

This is my understanding.

You start with a hypothesis with no assumption of truth. Using that hypothesis you make a prediction and then use observation to test your prediction. During your observation you may find proof that your prediction was correct, which in turn provides support for your hypothesis. Once sufficient evidence is found for a hypothesis, it becomes a theory.

[nonbel]

I'd say you have a theory from which you deduce a model that consists of various assumptions plus a hypothesis. If this hypothesis has not yet been compared to a set of observations, then it is also a prediction about that set of observations.

Also, the distinction between assumption and hypothesis is subjective, it depends what aspect of the phenomenon you care about at that time. Another term for assumption could be "auxiliary hypothesis".

Proof refers to the set of logical deductions (from theory + assumptions) that lead to the model, it has nothing to do with the observations.

[iamconfused]

It's important not to confuse theory with scientific theory. They have very different meanings. In everyday speech a theory is roughly equivalent to a guess. In science, a theory is a well tested explanation of some phenomenon.

It's always hypothesis then theory. Your hypothesis may be based on other theories, but it is itself not a theory.

From Wikipedia: "The scientific method involves the proposal and testing of hypotheses, by deriving predictions from the hypotheses about the results of future experiments, then performing those experiments to see whether the predictions are valid. This provides evidence either for or against the hypothesis. When enough experimental results have been gathered in a particular area of inquiry, scientists may propose an explanatory framework that accounts for as many of these as possible. This explanation is also tested, and if it fulfills the necessary criteria (see above), then the explanation becomes a theory. This can take many years, as it can be difficult or complicated to gather sufficient evidence."