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Just to give a bit more context:
* These are not elementary particles. * It was predicted for a long time that these composite particles should exist. So it is not "new" in the sense that it was unexpected, but we finally have the resolution (energy, luminosity etc.) to detect these with statistical significance. * These belong to the same class as protons and neutrons - these are hadrons made with multiple quarks.
Here's a super simple overview of Quantum Field Theory & Particle Physics:
Everything is made of force fields and matter fields.
* We discovered that force fields (i.e. electromagnetism) is quantized, giving rise to quantum mechanics etc.
* Matter fields are also quantized, hence their excitations behave like discrete particles - the ones we observe at the atomic scale, for instance.
* In hindsight, we should've been able to predict this after E = mc^2 telling us energy <> matter, thus if energy is quantized so should matter.
Energy isn't necessarily quantized though. For instance, the spectrum of an unbound particle is continuous. So why does it follow that matter should be quantized from E = mc^2?
-A curious physicist
I've never heard the term "matter field"... Is that a thing?
I assume you've heard of particle/wave duality, or how really tiny things are never exactly in only one place.
There are a set of wave equations that describe how this works.
There are also two kinds of things. Some things can go thru eachother, like photons. Other things bounce off eachother, like neutrons (and other things considered matter).
The equations for the kind of things that bounce off eachother would be a matter field.
There are also two kinds of things. Some things can go thru eachother, like photons. Other things bounce off eachother, like neutrons (and other things considered matter).
This is not true. The difference between bosons and fermions lies in the way swapping two of them works. The carriers of the weak force, W and Z bosons, are for example electrically charged and can therefore scatter off each other. Gluons, the carriers of the strong force, also interact with each other. Even photon photon scattering is thing. On the other hand you can try to collide two neutrinos, which are fermions, for quite some time and not much will happen.
The difference between bosons and fermions lies in the way swapping two of them works.
That sounds like what Wikipedia says is the rigorous version of the Pauli exclusion principle[1].
I was trying to get close to the not-rigorous version (1st paragraph of the link) in terms that are easily understandable without having taken a university QM course. I guess can/can't be in the same place at the same time would be a better approximation of it?
I have actually! And I also know about bosons and fermions. I didn't realize the phrase "matter wave" was just the name for the wave in wave-particle duality, that's all :) thanks!
They are properly called fermionic fields [1] as opposed to bosonic fields. I also want to note that the »super simple overview of Quantum Field Theory & Particle Physics« really is super simple. As far as I can tell - I am not a physicist - none of the statements is actually correct.
Matter fields are indeed a real thing. a Google Books search will reveal hundreds of books etc. They're also called fermionic field.
Here's the full range of elementary particles, all 19 of them, in the Standard Model:
Fermions:
- Leptons (6) (electrons, neutrinos etc.)
- Quarks (6) (protons and neutrons are made of this)
Bosons:
- Gauge Bosons (aka Force Carriers) (4)
- Higgs Boson (gives mass to stuff) (1)
What classical physics called force fields (i.e. Maxwell's equations), now we call them gauge bosons.
Electromagnetism : Photon
Strong Force: Gluon
Weak Force: W&Z boson
Gravity: No one knows!
One extra boson that gives everything mass - the higgs.
Force fields are quantized (see re: Photoelectric effect & Einstein's paper in 1905, winning a nobel).
Matter fields aka fermionic fields are also quantized, which makes these fields behave as if they are composed of discrete states -- giving raise to the particles & discrete states.
Indeed, in the Wikipedia article you link to, the first sentence reads: "fermionic field is a quantum field whose quanta are fermions".
ie: matter/fermionic fields are quantum fields, whose quanta are fermions, i.e. electrons, protons.
So, actually, all my statements are correct. Do you care to give a concrete example as to which one is not correct?
This is the best summary I've read (not that I've read much) but it really puts things in perspective.
Correct me if I'm wrong, but I'm going to try to summarize to make sure I understand:
The properties of protons, neutrons, and electrons that make them unique/distinct from each other (mass, electric charge) arise from the composition of each out of smaller particles, which each are/carry/act as the respective mass + charge + the other properties.
Is there any theory as to what this "looks" like? Or is the best we can do "it's a bunch of these things mashed together and the only way to see them individually is to bash them together until they break"?
If the strong and weak forces are particles, does that mean they're 1: literally everywhere, not necessarily stuck to any larger particle and 2: like glue?
I'm also confused about the relationship between gravity and mass, given that the higgs is stated as corresponding to mass, mass is traditionally thought of as what gravity acts upon, but the wikipedia chart states that gravity acts upon all particles.
What a rabbit hole...
We discovered that force fields (i.e. electromagnetism) is quantized, giving rise to quantum mechanics etc.
You are confusing quantum mechanics with relativistic quantum field theory. Quantum mechanics was developed as consequence of many different experiments showing quantization phenomena or requiring quantization to explain them, among them the spectrum of black-body radiation and the photo electric effect, but also the quantization of charge and spin. Quantum mechanics and non-relativistic quantum field theory are unable to describe electromagnetic fields, the former because it can not handle the creation and annihilation of particles, the later because photons are always relativistic particles and therefore require a relativistic description. Only with the development of quantum electrodynamics, a relativistic quantum field theory, was a quantum mechanical treatment of the electromagnetic field possible. But this was 20 or 40 years after the inception of quantum mechanics, depending on from where you count.
Matter fields are also quantized, hence their excitations behave like discrete particles - the ones we observe at the atomic scale, for instance.
It is important to understand, that quantum field theory is very different from quantum mechanics. In quantum mechanics a wave function describes the state of a system in Hilbert space, it describes properties of particles. But this runs into problems if the system contains many particles. Two electrons, for example, are indistinguishable and swapping them does not change the state, at least up to a sign change of the wave function which is the difference between fermions and bosons. This complicates the mathematical treatment. And as mentioned before, this approach is unable to handle the creation and annihilation of particles. Quantum field theory therefore takes a very different approach and describes with occupation numbers in Fock space how many particles are in each state.
In consequence the fields in quantum field theory are just a mathematical tool to handle many particle states. We started with particles and introduced fields to describe them mathematically, we did not discover that a field is quantized and therefore looks like a collection of particles. Admittedly this is a contentious issue, there are people claiming that those fields are real and more than a mathematical tool.
In hindsight, we should've been able to predict this after E = mc^2 telling us energy <> matter, thus if energy is quantized so should matter.
We knew or at least suspected that matter is quantized long before we discovered the photon, atoms and particles in general are a very old idea. So at best we could have inferred that energy is quantized from the quantization of matter, not the other way round. But the idea of photons actually predates E = mc², too. You are also probably misinterpreting what E = mc² actually says, you can not use it to link the quantization of energy to the existence of particles, at the very least not in any obvious way. The relationship between mass, energy, and particles is complicated.
And again, I am not a physicist, do not take what I say as the final truth, use it as a starting point. Corrections from actual physicist welcome.
I assume these particles were already predicted as part of the Standard Model?
Yes, but these experiments serve at least three purposes.
One, to verify the Model (after all, if its predictions fail in some part it will have to be revised).
Another, to verify the characteristics of the predicted particles (there might be some differences from the prediction that are important, but not hypothesis-breaking).
Finally, however unlikely and yet most excitingly (to me at least), to open new avenues of questioning and hypothesis up by really throwing into question some things.
It's worth remembering that the Higgs particle was also predicted by the standard model, and no one underestimates the importance of that confirmation.
The Higgs is an elementary particle, so its discovery was much more exciting. There are a lot of particles made up of quarks, like the five mentioned in the article:
http://pdg.lbl.gov/2016/tables/rpp2016-qtab-mesons.pdf http://pdg.lbl.gov/2016/tables/rpp2016-qtab-baryons.pdf
What is at least one single scientific (replicated) evidence that these tables does not contain merely a socially constructed crap, modern day alchemy deduced from flawed models and/or instruments?
Not in the same way. There was no experimental evidence for the Higgs field before the Higgs was observed. These new particles arise naturally out of parts of the Standard Model that are already experimentally tested.
You're not wrong, but you'd have been really hard-pressed to find someone of significance who didn't already believe the Higgs mechanism was there. In the sense that mass exists, there was a high degree of expectation there too. It's actually quite amazing to have so many of these recent discoveries, also be confirmations. It's been over a century of this, starting with Relativity.
Professor Tim Gershon, Professor of Physics at University of Warwick and UK spokesperson for the LHCb experiment:
“After the LHCb experiment is upgraded in the next long shutdown of the LHC (during 2019-20), it will be able to move to the next stage in the search for new particles: namely, doubly heavy baryons. These states – which contain two charm quarks or two beauty quarks or one of each – have long been predicted, but never yet observed. Their discovery will help to address important unsolved questions about how hadrons are bound together by the strong interaction.”
So I would assume that yes they have been predicted and is opening the doors for further confirmations?
Please take more care in quoting. What you've quoted does not describe the current work, but rather something they haven't demonstrated yet called "doubly heavy baryons". That sentence was immediately preceded by this one:
Professor Tim Gershon, Professor of Physics at University of Warwick and UK spokesperson for the LHCb experiment, explained what will come next for the LHCb experiment: “After the LHCb experiment is upgraded in the next long shutdown of the LHC (during 2019-20), it will be able to move to the next stage in the search for new particles: namely, doubly heavy baryons.
Yes, you are right, I miss read those paragraphs...
> 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)
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.
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.
Since QCD can't be calculated perturbatively at low energy, there are unsolved problems with how to get those predictions in the first place.
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.
There are a lot of baryons fyi:
Math tells me there must be 216, no? 3 quarks make a baryon, there are 6 types of quarks, so 6^3?
Idk if up up up baryons are allowed though, or any other baryon made of 3 equal quarks.
AFAIK, the experimentally determined rest masses of these excited states/particles (same thing, different was of looking at it) agree with the calculated ones well. So yes, they were predicted. No surprises sadly; of course it's still a huge achievement!
The theory uncertainties are large. Any measurements within a broad range would also agree with some calculated masses. That doesn't tell you much.
See e.g. https://arxiv.org/abs/1311.4806
yes, and note that these are not fundamental particles (like the Higgs was for example), but composite particles of yet another combination of the fundamental quarks. The SM predicts the existence of hundreds (thousands?) of these.
Actually it is even a one new particle (Omega_c baryon), but they observed five different excited energy states of it (like observing different excited states of a Hydrogen atom), so called resonances [1]. But the discovery is still exciting because it should have been really hard to find something that we don't really know how looks like in such large amount of noise.
The problem is that it is hard for us to predict masses/energies of new composite particles because although Standard Model provides hypothetical way to do it, it is infeasible computationally.
[1] http://physics.stackexchange.com/questions/64862/resonances-...
>"it should have been really hard to find something that we don't really know how looks like in such large amount of noise."
But if there are thousands of different such "surprising-to find-particles" to possibly detect, is it actually surprising to observe one of them?
Edit:
Also, from the top answer at your link: "The first generation of elementary particles are by observation not composite and therefore not seen to decay...The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column and the Higgs boson in the fifth."
From wikipedia: "In the Standard Model, the Higgs particle is a boson with no spin, electric charge, or colour charge. It is also very unstable, decaying into other particles almost immediately." https://en.wikipedia.org/wiki/Higgs_boson
So do elementary particles decay or not?
Yes. They're baryons (three-quark states). This is analogous to the discovery/synthesis of new isotopes in the middle of the last century. Technically they were "predicted", but it's still important to take the measurements. Occasionally there are surprises.
For more in-depth information see the CERN press release "LHCb observes an exceptionally large group of particles" at https://home.cern/about/updates/2017/03/lhcb-observes-except...
Or, the paper "Observation of five new narrow Ω0c states decaying to Ξ+cK−" is available at https://arxiv.org/abs/1703.04639
And finally, the LHCb web site section on "Observation of five new narrow Ωc0 excited states" at http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#Omeg...
I have to admit, I rather admire their putting a brave face on things, with their mildly-too-insistent claim that the LHC is vital for finding new physics despite the increasing likelihood it's not going to find any.
In that sense the LHC is a political failure, because it has failed at its primary political job, which is to make the argument for an even bigger collider.
You know, it's ok not understand much about high energy physics, it's a complicated and somewhat obscure field. It's ok not to understand about what's already been achieved at the LHC, and what might still be over the decades.
What's not ok is to pontificate from that seat of ignorance.
How'd it fail at it's primary task? Wasn't the Higgs a big part of that? Or is the argument that is hasn't found anything outside of the standard model?
It succeeded at its primary task, and the Higgs was a big part of it. Its still doing its job, so give it time. Finding nothing can often be just as important as finding something unexpected.
Mapping an open field fills in just as much paper as if you mapped a busy forest.
I'm not sure what the best way is to convey this idea since people naturally want to find things that are exciting.
> Finding nothing can often be just as important as finding something unexpected.
From a scientific point you are right. From a political point or the point of securing further funding this statement is (unluckily) wrong.
The physics community does not consider finding the Higgs new physics. Not finding Higgs would've been more exciting, or a more massive / lighter Higgs, etc. The Higgs showed up exactly as predicted with the predicted mass, so we're stuck with the Standard Model - i.e. no "new physics".
Well, I don't know if the LHC is a vital instrument but it will certainly decide were the community of particle physics will go after the plug is pulled on it.
The little I know about is that the LHC is an hadron collider (of course, duh), which means the collisions are not as "clean" as they were with the LEP collider, because the energy is not "deposited" on elementary particles like electrons but on composite hadrons. Which apparently makes things more complicated when it comes to know exactly how the energy is distributed inside the hadrons when they collide...
I'm not sure, I'm not an expert :) I've read that the next collider should use electrons again for collisions, up to 1 TeV or more. Maybe using linear accelerators...
Even if the analogy is not very good it's a little bit like the James Web space telescope, it will open new horizons and open the way for more precise exploration with 50m-class optically stabilized terrestrial telescopes... Just like actual 10m-class telescopes have studied Hubble discoveries in more details.
I see the LHC the same way. The results they will gather from it will decide what to explore next, with more a "precise" collider using leptons and "clean" high energy collisions.
Maybe I'm wrong though. On the political side of thing, sure, it's a costly adventure but I'd rather see money spent on those big scientific project than throwing money at military spendings and engage in useless and illegal wars.
That doesn't mean we can't debate big scientific project. ITER is also a monstrous one when it comes to budget and is even more risky because of the disruptions problem when it comes to confined unstable plasmas in a Tokamak chamber. An apparently 70 years old unsolved problem. Some physicists have warned about powerful disruptions, because of the size of ITER and induced currents in it, potentially harmful for the installation and the people that will work on it if the Tritium breeding blankets are destroyed...
Still, it will be made. And an even bigger experimental reactor is planned, DEMO, that will cost even more. I'm more sceptic about ITER than the LHC...
None of that makes any sense.
You're jumping the gun a bit there. The general purpose experiments have only collected O(1%) of their eventual datasets.
I know what you intended, but technically O(1%) == O(100%) == O(5000%)
LHC is a science experiment. Its job is to, first, check older results [1], and second, put nature to the test in a well-motivated and important way. In particular, LHC is the Higgs hunter, a messy [2] pathfinder before a precision Higgs-studying tool. It succeeded at that job [3].
That LHC has found no new physics beyond the standard model is not a failure. Finding nothing where you thought you might find something is as useful as finding something. If anything, it is more interesting, as it means there is still far more to be learned.
Politics are about people. The science case is a driver for the political case, but it generally takes a backseat to other goals when funding is at hand. First, science keeps us sharp. It pushes harder on materials and technology than anything ever done. An investment in science is also an investment in the entire science supply chain. The recent explosion of quantum-computing hardware investment has only been possible because scientists have built and sustained the tooling and companies that manufacture the necessary subcomponents at a reasonable cost.
More important, it teaches us how to learn; our most important product as scientists is our students. Students keep the field alive, yes, but most students take their new skills, knowledge, and curiosity with them to share outside of academia. Furthermore, governments support scientists to retain the skills for when they are needed by the populace in general; when the Fukushima accident occurred, our laboratory dropped everything it was doing in order to focus on atmospheric monitoring [4].
Finally, the fundamental knowledge we glean from each halting step forward moves us forward as a species. The device on which you are reading this text is the aggregate product of millennia of fundamental research and refinement.
LHC, at least from my outside perspective (I would benefit personally if less money were directed to colliders), has been well-run, successful, and worth the price, both scientifically and politically.
Where we go next is an interesting question -- I'd place my money on exotic accelerator technology. The detectors are wonderful, and linear accelerators are the century-scale path forward. The trick is finding a revolutionary new accelerator idea.
[1] Which it did beautifully. Really beautifully, and really fast. Look at Figure 3: http://lss.fnal.gov/archive/test-fn/0000/fermilab-fn-0923-cm...
[2] Protons are full of quarks and gluons, so when they collide, it's difficult to know which component hit which other component. Lepton-antilepton colliders, on the other hand, are harder to build, but extremely clean.
[3] There is one Higgs. Its mass is 125.09 ± 0.24 GeV. Its width is less than 1.7 GeV. It is the first fundamental scalar particle known to man. http://pdg.lbl.gov/2016/tables/rpp2016-sum-gauge-higgs-boson...
[4] https://arxiv.org/abs/1103.4853 , https://www.npl.washington.edu/monitoring/node/1