What changed to make a slew of new discoveries possible? Is it pure chance like Bitcoin mining? If so, what's the chance of discovering nothing for years and then, like London buses, three all come along at once?
What are the implications of a new "particle zoo"? Can I do anything with these, like build new atoms, or use them to detect something?
I think the goal of this work is to understand the nature of the strong force. Quantum chromodynamics (QCD) is pretty difficult as far as quantum field theories go, its strongly-coupled, meaning making first-principles predictions of what to expect is really tough. Its a huge computational effort being run on some of the biggest computers on the planet (lattice QCD).
We observe that all the hadrons in experiment are "colour singlets" meaning that the colour charge of QCD is hidden. These are usually three-quark states (protons, neutrons, etc) or quark-antiquark states (pions, kaons, etc). There are many other ways of making "colour singlets". For example, these tetra and pentaquark combinations. There are also "hybrids" made of a gluon and some combination of quarks. There is some evidence on both experimental and theoretical sides for at least a few of these hybrids. Glueballs are also possible, states made entirely of gluons, but there is only really theoretical evidence for these so far in specific limits. We just don't know if they exist in reality.
Everything is made of this stuff. Most of the mass around us comes from the strong interactions. It's important to understand it.
I think people are a bit spoiled by the Higgs leak/announcement/discovery timeline. I'm sure those in the know have known about this discovery for some time but, like you said, it takes some time to gather enough data to be confident (and to qualify as the mathematical standard set for "discovery").
"Sigma" here refers to standard deviations off the Gaussian normal mean. Zero means completely random. In psychology they publish at 2x sigma, 95%, which means 20:1 odds against a spurious result, and they publish a lot of spurious results because you can generate an unlimited number of hypotheses. In physics, things are considered more deterministic, and an experiment doesn't need to recruit undergrads to be data points, so you run your LHC for a few more months and avoid wasting people's attention.
However, the approach taken by CERN is of course right. They find a result at a certain significance level and then collect more data to verify the result. As long as there aren’t thousands of simultaneous verifications running, this approach is sound. Obviously yes, physicist’s know what they’re doing.
Having said that, please don’t read this comment as me approving of frequentists statistics. Bayesian or cross-validations are way easier to interpret where possible.
But more idiot's questions if you have any thoughts....
My understanding was that particle accelerators were being used to try and deconstruct matter, to do for want of a better word "fission" by smashing things together and seeing what smaller bits came out - by analogy to mass spectrometry.
What seems to be going on now is that we're trying to make new particles. Have we switched to a sort of "fusion" - to see if smashing things together will get them to stick in bigger configurations?
Have all the most fundamental bits (quarks?) been found now? Can we prove that those are irreducible?
chreers
That energy forms into a bunch of particles, each of which will then decay into less esoteric particles.
We have no proof (and it's probably impossible to do so), that anything we've found is fundamental.
This is a good statement.
I've seen many online state that quarks are fundamental.
There is no way we can make such a definitive statement.
Quarks may be not be fundamental.
We will never, in the lifetime of anybody who guesses we ever existed, be able to build an accelerator powerful enough to check whether it is right about gravity. So, they potter and try to show this or that family of variations (among 10^500 imagined) does or doesn't contradict details of the Standard Model we have most confidence in.
But using current accelerator technology it would require an accelerator many times the size of the earth, _many_.
I use to work at a particle accelerator, part time, when i was in college. Fun fact i once confirmed Einsteins photoelectric effect using a high energy x-ray beam, a copper target, and high voltage.
It's not possible to do better than that, though, because you can't prove a negative statement like "there are no more fundamental particles". Even if we understood the laws of physics completely, they could always change on us. It's all up to the guy who owns the universe simulator.
I sense that the next step in physics and ontology can only happen when we have created a new linguistic approach to capture the 'fundamental' idea here.
All other particles would be derivative, and their being caused by some base rules.
Physics will only be complete when fully explained in terms of information, regardless of the physical reality of information. The two aspects of explanation are 1. the rules and 2. what are the bits? Perhaps both those things are one.
Perhaps bits are not fundamental and quaternary bits are, but that would still implicate information as fundamental.
this entire discussion is fully outside of my knowledge wheelhouse but why should we believe that the universe is anything less than infinitely fractal at the micro scale? like you said, how would we even know if something is fundamental?
And what basis does that claim rest on
Physics has had the other problem for a while now - they know the current theory is wrong, but they can't find any evidence to disprove it, and it's wasting generations of scientists and particle accelerators to do it.
Follow-up question. Why don't quark anti-quark combinations self annihilate?
I've been trying to understand this.
In the pentaquark, charm-anticharm annihilation can and will happen. The time for charm-anticharm annihilation is usually slower relative to light and strange hadronic interactions though. In part because the strength of strong interactions reduces at higher energies, and the charm quark is more massive and so the relevant energy scale for the decay is higher.
One charm-anticharm resonance, the J/psi(3097) is very long lived even though the quarks can annihilate. In many theoretical models of these things, its often treated as a stable particle.
When particles are collided and the result measured, there's probably lots of noise in the data. In a single picture, a single pixel (datapoint) tells you nothing. But capture enough results, and you can begin to filter the noise out, revealing patterns underneath.
[1] https://bigthink.com/hard-science/large-hadron-collider-econ...
First, there was a pretty constant stream of these kinds of discoveries over the last years. Most of them even discussed here [1, 2, 3 and more]
Second, what you need to find these rare events are two things: enough statistics and someone actually doing a specialized analysis looking for them.
Enough statistics have been accumulating over the past years, and now someone stepped forward, developed the analysis, tested it on small scale dataset, got it approved by the Collaboration, ran it on the large dataset and then chances are that you don't just find one but three very similar things.
Disclaimer: I am not part of LHCb and have no insight into the specific analysis of this discovery, just sitting on the same floor as the LHCb guys and knowing the general procedure.
Third, as noted in a sister comment, these quark states are expected from the standard model, they are just very rare and very short lived, so hard to find. Nothing new normally refers to "no physics found incompatible with the standard model".
[1] https://home.cern/news/news/physics/lhcb-experiment-discover...
[2] https://cerncourier.com/a/new-pentaquarks-resolved-by-lhcb/
[3] https://physicsworld.com/a/lhcb-bags-another-pentaquark/
These newly discovered particles are composed of multiple quarks and were found (at least up to the measurement precision) with the expected rules of how you can combine the elementary particles into composed particles (Baryons in thos case).
LHCb actually discovered a bunch of those in the last couple of years.
But these are expected from the standard model, just rare and thus not experimentally confirmed before.
"Nothing new" for LHC means no new physics. And if these quark states don't happen to be much more frequent or much more rare than predicted, there is no new physics here.
Means we are in a pretty tricky timeline.