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> The change is the gradual accumulation of statistics. These are relatively rare events. The LHC has been running, high-energy proton-proton collisions have been occurring, and the LHCb detector in this case has been measuring them. The statistics increase, and eventually the characteristic peaks of short-lived resonances can be identified above the noise of "background" collisions.

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").

Right, after the bump reaches 3x sigma they have some confidence it deserves their own attention, and at 4x they are sure, but the rule is you don't publish until you have enough data for a 5x sigma result, which just takes a lot more data and a lot longer.

"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.

The chance of falsely rejecting the null hypothesis increases as you gather more data. Put more simply, finding something that differs "significantly" from some distribution becomes easier as you gather more data. Imagine having only 3 psychology student in a study, the required effect size has to be huge for the test to say that it is significantly different.

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.

I would never accuse you of frequentism. But if you and a frequentist ever get different answers, one of you just made a booboo.

Thanks for trying to explain. It's all still largely beyond me TBH.

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

Essentially, you smash particles together. When you do so, they will give off a bunch of energy.

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.

> 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.

What would it take to actually prove that they are? I did miss the "impossible" above when first posting this -- but pretend it isn't?

This is the problem String theorists have.

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.

it would require being able to generate a high enough energy beam

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.

How do we even know that the universe has fundamental particles?

In our basest theory QFT, no particle is fundamental because they're actually "fields" - but those fields are fundamental so that doesn't answer your question. We just think they're fundamental because we don't have enough evidence to construct anything better than the Standard Model.

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.

But doesn't fundamentality in fields imply something quite different than fundamentality in parts (particles)?

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.

It may not.

https://en.wikipedia.org/wiki/Gunk_(mereology)

That sent me down a fascinating rabbit whole on Wikipedia. Thank you!

The Planck constant appears fundamental.

If information is physically fundamental, the fundamental "particle" would be some sort of bit. Planck's constant could be that bit.

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.

> We have no proof (and it's probably impossible to do so), that anything we've found is 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?

> why should we believe that the universe is anything less than infinitely fractal at the micro scale

And what basis does that claim rest on

sheer intuition based upon the adage "you don't know what you don't know", repeated incorrect assumptions that we've finally discovered fundamental building blocks of reality, and lack of capacity for imagination (sorry—I tried!) for what the discovery of absolutely positively provably fundamental building blocks of reality could even potentially look like

> repeated incorrect assumptions that we've finally discovered fundamental building blocks of reality

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.

I disagree. Not that you're wrong but that you're right.

???

The Planck constant isn't infinite.

Probably also just time: time to run more experiments, time to improve analysis compute capability, and to analyze new data and re-analyze the data they already have. These experiments yield enormous amounts of data.

Thank you for this explanation.

Follow-up question. Why don't quark anti-quark combinations self annihilate?

I've been trying to understand this.

They do. The Tcs0 tetraquarks don't have quark-antiquark pairs however, you see from the article and figures, that the quark content is charm + anti-strange + up + anti-down, these can't annihilate because the quarks have different flavours. They can "annihilate" via the weak interactions though, which can connect quarks and anti-quarks of different flavours. For example the charm-antistrange part could decay via a W-boson to a positron and a neutrino. This is a much slower process however.

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.

The particles are very shortlived, so the brief answer is that they do.