How does the strong force give nucleons most of their mass?

[Ignorantsmith12]

TL;DR Summary

I've heard three different explanations for how the strong force gives nucleons their mass.
1. The force is incredibly strong therefore much energy and E=MC^2
2. The glueon field has particles bumbling in and out of existence.
3. The glueon field is like a Higgs field.
Which, if any, of these explanations if any is true?

First, I did read this article on Byrons: https://www.physicsforums.com/insights/a-beginners-guide-to-baryons/. If the answer to my question is in there, I'm sorry, but I missed it somehow. Honestly, much of that article went over my head.

Other than that, it's as the TLDR says. I have heard these three different explanations for how the strong force that gives mass to nucleons and have no idea which one, if any, to believe. By the way, I've also heard some of the particles suddenly materializing for microseconds can be larger than the nucleon itself. If that's true, I would love to know how that works.

As for the Higgs field analogy, going into detail about the Higgs field might be for another thread. Suffice it to say that I have heard that the Higgs field is not like mud, and that is a lazy explanation.

 

[Vanadium 50]

None of them are right.
All of them are right.

Popularizations are what they are - an imperfect description of something that takes years of schooling to fully understand. Have you ever heard the tale of the blind men and the elephant?

 

[Ignorantsmith12]

.

...Popularizations are what they are - an imperfect description of something that takes years of schooling to fully understand...

I assumed that was true of all science. I don't pretend to know Newtonian physics just because I can throw a ball. Even so, verbal explanations for this and other phenomena are possible, even if they can never be as complete as a mathematical explanation.

Does this mean there is something unique to this question of the strong force, and how it creates mass that makes it impervious to verbal explanation? If so how do researchers write papers on it? I mean, such papers do tend to have a small verbal component to them. Is it possible to write a paper without one? If so, can I see it? I won't understand it, but I would think it's cool if people have figured out how to do that.

 

[PeterDonis]

verbal explanations for this and other phenomena are possible

If you don't need to actually understand the physics, in the sense of being able to make predictions, sure.

Does this mean there is something unique to this question of the strong force, and how it creates mass that makes it impervious to verbal explanation?

No, it means that verbal explanations by themselves don't give you an actual understanding of the physics, as above.

If so how do researchers write papers on it?

Because the researchers use math in their papers, and math is how physics is actually done--how models are built and predictions are made and compared with experimental data. Yes, there are also words in the papers, but the words by themselves, without the math, don't give you an actual understanding of the physics, as above.

 

[PeterDonis]

I have heard these three different explanations for how the strong force that gives mass to nucleons and have no idea which one, if any, to believe.

If all you care about is what to "believe", i.e., if you don't care about actually understanding the physics but just want some comforting story to "believe", then just pick one. It won't matter anyway since you won't be using your "belief" to guide any actual action on your part.

 

[Ignorantsmith12]

Forgive me, but couldn't the responses here apply to any other thread on this forum? If someone ask a question about the twin paradox, can't someone just say "You need special schooling to understand this." and leave it at that? That's the truth, after all. I guess I'm confused because I'm only seeing that message in regard to this question.

Look I know I will never know the universe the way a physicist does, but I do want to know the truth best I can, and if the response must often be "You must know math," that's fair, but what about all the other subjects on this forum. And what the other lay people who sometimes have question on this forum? How does that work?

 

[PeterDonis]

couldn't the responses here apply to any other thread on this forum?

No. The point is that you are not even asking for the math. You are not asking to actually understand the physics. You are just asking for a verbal description. That's not true of other threads on this forum.

I do want to know the truth best I can, and if the response must often be "You must know math," that's fair,

If it's fair, why are you protesting when you get that response?

what the other lay people who sometimes have question on this forum?

Many other people also get the response that the physics can only be properly understood with math.

 

[Ignorantsmith12]

ok, ok, ok. First, let me apologize. I did not mean to protest. I regret being so dismissive of math, and you're right. I need to put more effort into learning math. Also, anyone who can get their PhD in physics is way smarter than me and is doing very important work, and I am great full that you and other would take time away from that important work to talk to me. I am really sorry.

Now before I say anything else, may I be forgiven.

 

[PeroK]

First, I did read this article on Byrons: https://www.physicsforums.com/insights/a-beginners-guide-to-baryons/. If the answer to my question is in there, I'm sorry, but I missed it somehow. Honestly, much of that article went over my head.

I wrote that insight. The term beginner is relative of course.

It doesn't tackle the thorny issue of mass within the standard model of particle physics.

The strong force is highly non-classical, which makes it difficult to describe. I always thought of gluons more as mathematical than physical entities. In mathematics things are defined by their properties. And the edifice of the standard model is built on mathematical concepts, such as symmetry and superposition.

The electron is something of an exception as it emerges from the model and manifests itself in ways that can be more readily understood in classical terms.

The photon can be understood to some extent in classical terms, although the quantum theory of light is highly non classical. Try Feynman's Strange Theory of Light and Matter.

Quarks and gluons have no manifest interaction in the classical realm. They are buried in an abstract mathematical model. This was one of the ideas I hoped to convey in the Insight.

 

[PeterDonis]

Quarks and gluons have no manifest interaction in the classical realm.

One aspect of this which is relevant to the current thread topic is that the usual classical concept of "binding energy" doesn't work for hadrons (baryons and mesons). The usual classical concept of "binding energy" is the energy you would have to add to a bound system to separate it into its constituents. For example, the binding energy of a hydrogen atom in its ground state, 13.6 eV, is the energy you would have to add to separate the atom into a free proton and a free electron. That means, in turn, that the mass of a hydrogen atom in its ground state is slightly smaller than the mass of a free proton plus the mass of a free electron.

However, for a baryon or meson, it is impossible to separate it into its constituents; the strong interaction simply doesn't allow it. So, for example, it is impossible to separate a proton into three free quarks. So it doesn't even make sense to ask the question of why the proton's mass is much larger than the sum of the masses of two up quarks and a down quark, instead of being slightly smaller. The whole concept of the mass of the proton being "made up" of the masses of three quarks plus some binding energy doesn't work for a proton (or any other hadron). Indeed, the quark "masses" themselves don't really have the same meaning as the mass of, say, an electron, where we can measure an electron's properties as a free particle, in isolation from other particles.

 

[Ignorantsmith12]

... The whole concept of the mass of the proton being "made up" of the masses of three quarks plus some binding energy doesn't work for a proton (or any other hadron). Indeed, the quark "masses" themselves don't really have the same meaning as the mass of, say, an electron, where we can measure an electron's properties as a free particle, in isolation from other particles.

Ok I guess option one can be crossed off my list. Nice!

Anyway, I guess I will just have to have to work towards the true explanation. Before I go though, is there a single paper that describes how the solution was arrived at? I won't be able to understand it now, but like I said I will just have to work towards it.

 

[mitchell porter]

You could try the most recent paper by Craig Roberts (who often writes on this theme), "The Origin of the Proton Mass".

 

[Nugatory]

I don't pretend to know Newtonian physics just because I can throw a ball. Even so, verbal explanations for this and other phenomena are possible, even if they can never be as complete as a mathematical explanation.

Verbal explanations can work reasonably well for a lot of Newtonian physics (not always - how would you explain the precession of a gyroscope without some math in there somewhere?) because we have an entire lifetime of experience with classical phenomena so our intuition has a solid base upon to build.

Quantum mechanical phenomena, not so much. It's hard to construct effective analogies without something to compare to, and nothing in our classical experience works for that. Thus even the best efforts by bona fide experts eventually run up against the accurate but deeply frustrating answer @vanadium50 gave: They're all right, they're all wrong. And it's not V50's fault that it's frustrating, none of asked to be put in a universe whose fundamental rules are inconsistent with classical thinking.

 

[ohwilleke]

TL;DR Summary: I've heard three different explanations for how the strong force gives nucleons their mass.
1. The force is incredibly strong therefore much energy and E=MC^2
2. The glueon field has particles bumbling in and out of existence.
3. The glueon field is like a Higgs field.
Which, if any, of these explanations if any is true?


As for the Higgs field analogy, going into detail about the Higgs field might be for another thread. Suffice it to say that I have heard that the Higgs field is not like mud, and that is a lazy explanation.

Option 3 is the least true. Option 1 is closer to the truth than Option 2. None of them are perfect (and by the way, the carrier boson of the strong force is spelled "gluon").

The Higgs field imparts mass to quarks, charged leptons (i.e. electrons, muons, and tau leptons), weak force bosons (the W and Z bosons), and the Higgs boson. The mass of these fundamental particles influences the mass that is created by the strong force and its constituent fundamental particles, but this effect is only indirect.

Photons and gluons don't have any rest mass (at least in theory) and are never "at rest" but the energy of these particles can be substituted for mass when evaluating the mass of a particle using the E = mc² formula.

Neutrinos have tiny but non-zero mass, but we aren't really sure where it comes from and there are competing theories about that at this point.

However, for a baryon or meson, it is impossible to separate it into its constituents;

I would also take issue with this statement.

A hadron is a system made up of quarks and gluons bound together by the strong force.

While you can't physically measure the mass of free quarks or use the same mass definition that you do for binding energy in an atom, that doesn't mean that there aren't sensible ways to separate out the mass of the constituent parts of a hadron analytically.

You have to be clear about the definition of quark mass that you are using, because there are several different competing definitions of it, each of which has subtle pros and cons.

But, the most widely used definitions do assign well-defined masses to each kind of quark with a value that is the same at any given energy scale, no matter what hadron the quark is a part of (indeed, these are experimentally measured physical constants of the Standard Model and match up also to the strength of that particle's coupling to the Higgs field called a Yukawa, which can be independently determined from Higgs boson decay frequencies). The mass of the top quark can also be measured much more directly, because it decays via the weak force before it can be bound into a hadron and has a mass of about 173 GeV plus or minus. The very reasonable definitions of the quark masses are discussed, for example, by the Particle Data Group in this review article.

For example, one can look at hadrons that are identical except one valence quark, and then use the difference between the masses of the two hadrons to provide insight into the differences in the masses of the quark that is different. It's more complicated than that, but that's the gist of the idea.

The total "invariant" mass of a hadron with particular quantum numbers and particular valence quarks is a well-defined number, that isn't really a function of the virtual particles in the "particle sea" of that hadron at any particular time.

But, experimentally, for any given hadron, what you really end up with as the output of your measurements of the hadron's mass is really a curve over a range of masses derived from many individual data points, with a peak and gradual fall offs higher and lower, which is called a "resonance", and not just a single data point. A generic example of what the output of your experiment measuring the mass of a resonance looks something like this:

You really need both the mass of the peak of that resonance M(Z) which is the "invariant" mass and what you are most likely to measure experimentally, and the width of the resonance, Γ(Z) which indicates the extent to which a measurement is off that peak (and is also related to the mean lifetime of the particle), to understand a particle's mass (in this case, a Z boson) fully.

The way that you interpret the mass of the particular components, and the definitions of the quark masses that you use, is to some extent a function of why you need to know those values.

But, for most purposes, it is most useful to think of the mass of a hadron as made up of the mass of the valence quarks of the hadron (defined according to one of the typical definitions of that, such as the MS Bar definition, and once scientists measuring quark masses work them out, determinable from a reference source like the Particle Data Group) and then to use that one definition that you choose to use consistently. Then, the balance of the mass of the hadron is generally attributed to its strong force field made up of gluons being exchanged by quarks.

This is what someone is doing when they say, for example, that about 1% of the mass of the proton is made up of its valence quarks (two up quarks and one down quark, with a combined mass in the most common definition of light quark masses of about 9-10 MeV, with significant relative measurement uncertainties) and the balance attributed to the strong force field of the proton.

When you use this approach, all hadrons are more massive than the sum of their valence quark masses. But, proportionately, hadrons with lighter valence quarks tend to have a small proportion of their total mass attributed to their valence quarks, while hadrons with heavier valence quarks tend to have a larger proportion of their total mass attributed to their valence quarks.

This makes sense because the strong force couples to a quark's strong force color charge, and every quark has a strong force color charge of the same magnitude.

But, the relationship between total hadron mass and its component sources is also not as simple as the sum of the valence quark masses plus a strong force field mass equal to the number of quarks in the hadron adjusted for their spin. There is some feedback between the two quantities, which can be calculated using approximations of the Standard Model theory of the strong force known as QCD. Predominantly, this is done using an approach known as Lattice QCD.

 

[PeterDonis]

I guess option one can be crossed off my list.

No, it can't, because what I said does not mean that the properties of the strong interaction do not involve energy and do not make a significant contribution to the mass of the proton.

 

[PeterDonis]

I would also take issue with this statement.

You're not taking issue with it. You're agreeing with it:

you can't physically measure the mass of free quarks

Because there is no such thing as "free quarks" in isolation. Nothing you say contradicts that.

There are certainly ways of indirectly assigning a "mass" to quarks, but, as you note, there is no unique way of doing so. Which in itself is already enough to show that the OP's "options" are too simplistic.

 

[ohwilleke]

You're not taking issue with it. You're agreeing with it:


Because there is no such thing as "free quarks" in isolation. Nothing you say contradicts that.

There are certainly ways of indirectly assigning a "mass" to quarks, but, as you note, there is no unique way of doing so. Which in itself is already enough to show that the OP's "options" are too simplistic.

“People who say it cannot be done, should not interrupt those who are doing it”​

― Bernard Shaw

 

[PeterDonis]

“People who say it cannot be done, should not interrupt those who are doing it”​

― Bernard Shaw

Is this relevant?