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What Does It Mean For A Proton To Contain "Intrinsic Charm"?
32 Answers
I've read this several times and I still don't understand how it makes sense. How can a proton contain a particle that's heavier than it is?
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"Intrinsic, meaning naturally.
Protons were/are thought to consist of 3 quarks (2 up and a down) and loads of gluons.
Latest results suggest it may also have at least 1 further quark, a charm one."
I understand that bit but it still does not make sense to me how a proton can have another quark inside that's heavier than the proton is.
Protons were/are thought to consist of 3 quarks (2 up and a down) and loads of gluons.
Latest results suggest it may also have at least 1 further quark, a charm one."
I understand that bit but it still does not make sense to me how a proton can have another quark inside that's heavier than the proton is.
I don't quite understand how a proton could contain an Intrinsic Charmed Quark when its mass exceeds the mass of a proton.
I can understand an Intrinsic Strange Quark being there. Its mass plus the mass of the two Up and the Down Quark is still less than the proton, much of whose mass comes from binding energy.
I can understand an Intrinsic Strange Quark being there. Its mass plus the mass of the two Up and the Down Quark is still less than the proton, much of whose mass comes from binding energy.
I'll try to get back to this later in the week. Beso's answer so far is the closest.
"Mass" when it comes to quarks is a seriously complicated beast. But the bottom line is that:
1) defining masses for quarks is already complicated, and depends to an extent on what the quark is even doing;
2) any standard intuition that, say, the mass of some compound object, like a proton, is necessarily larger than the sum of the constituent masses isn't correct, because you have to consider how the pieces interact with each other.
"Mass" when it comes to quarks is a seriously complicated beast. But the bottom line is that:
1) defining masses for quarks is already complicated, and depends to an extent on what the quark is even doing;
2) any standard intuition that, say, the mass of some compound object, like a proton, is necessarily larger than the sum of the constituent masses isn't correct, because you have to consider how the pieces interact with each other.
It's probably worth trying to answer this in several parts. I don't want to talk about intrinsic charm at all to start with, because it's complicated enough as it is. Instead I wanted to talk about things related that might help to clarify how this could make sense.
Firstly, I think it's helpful to emphasise that mass is a measure of how reluctant something is to move. The more mass, the harder it is to move -- eg, the more energy required to get it moving at a given speed, or the more force to accelerate it a given rate. The connection with energy is particularly helpful here because you can imagine that if the system has some interactions itself, that might change what something that's looking at the system as a whole measures. In other words, the mass of a system as a whole depends on what's going on inside that system.
Starting, say, with atomic nuclei. So, for example, Oxygen contains eight protons and eight neutrons. Its mass is then naively going to be the sum of these, which is (in atomic mass units)
8*1.0073 + 8*1.0087 = 16.13
but we measure the mass of oxygen in the same units to be about 15.999, which is somehow less. How is this? The answer is that interactions between the protons and neutrons serve to lower the effective mass. This is the "binding energy", which can be described using the method in the wiki page below:
https:/
For an intuitive picture of what's going on here, the strong force, the interactions between protons and neutrons, "takes away" mass because the particles *want* to be together. On the other hand, the repulsive force between the protons, the "Coulomb interaction" in that wiki pink, acts to push things apart and increases the mass, by increasing the energy required to hold this system together. I don't see the point in explaining the other two terms, the "asymmetry term" and "pairing term", but they're trying to measure other effects and again can either make it easier or harder to hold the system together. In any case, they alter the internal energy of the system.
The upshot is that the mass of a nucleus is less than the mass of the particles inside it, because they are interacting with each other, and changing the energy of the state. It doesn't really matter how those interactions work, the point is that the mass of a combination of particles is equal to the sum of the individual masses, *plus* or *minus* some corrections.
Linking back to intrinsic charm, with no further details we could at least imagine that the mass of a proton receives a contribution from the mass of the charm quark, but either:
i) *minus* some corrections, so that even if on its own the charm mass is more than the proton mass, those corrections balance it out, or;
ii) have the charm mass multiplied by something that tells us "how much" of the proton is really charm.
I'll try to explore both later, I'd need to study the paper in more detail, but the real point I want to emphasise, again, is that the mass of any combination of things isn't just the sum of its individual pieces.
Firstly, I think it's helpful to emphasise that mass is a measure of how reluctant something is to move. The more mass, the harder it is to move -- eg, the more energy required to get it moving at a given speed, or the more force to accelerate it a given rate. The connection with energy is particularly helpful here because you can imagine that if the system has some interactions itself, that might change what something that's looking at the system as a whole measures. In other words, the mass of a system as a whole depends on what's going on inside that system.
Starting, say, with atomic nuclei. So, for example, Oxygen contains eight protons and eight neutrons. Its mass is then naively going to be the sum of these, which is (in atomic mass units)
8*1.0073 + 8*1.0087 = 16.13
but we measure the mass of oxygen in the same units to be about 15.999, which is somehow less. How is this? The answer is that interactions between the protons and neutrons serve to lower the effective mass. This is the "binding energy", which can be described using the method in the wiki page below:
https:/
For an intuitive picture of what's going on here, the strong force, the interactions between protons and neutrons, "takes away" mass because the particles *want* to be together. On the other hand, the repulsive force between the protons, the "Coulomb interaction" in that wiki pink, acts to push things apart and increases the mass, by increasing the energy required to hold this system together. I don't see the point in explaining the other two terms, the "asymmetry term" and "pairing term", but they're trying to measure other effects and again can either make it easier or harder to hold the system together. In any case, they alter the internal energy of the system.
The upshot is that the mass of a nucleus is less than the mass of the particles inside it, because they are interacting with each other, and changing the energy of the state. It doesn't really matter how those interactions work, the point is that the mass of a combination of particles is equal to the sum of the individual masses, *plus* or *minus* some corrections.
Linking back to intrinsic charm, with no further details we could at least imagine that the mass of a proton receives a contribution from the mass of the charm quark, but either:
i) *minus* some corrections, so that even if on its own the charm mass is more than the proton mass, those corrections balance it out, or;
ii) have the charm mass multiplied by something that tells us "how much" of the proton is really charm.
I'll try to explore both later, I'd need to study the paper in more detail, but the real point I want to emphasise, again, is that the mass of any combination of things isn't just the sum of its individual pieces.
I'm really not sure if I'll have time to read the paper and comment on what's going on in more detail. I will try, at least.
The key concept to get a handle of, though, is that "mass" is not really (or at least not exclusively) a measure of the amount of stuff. It's a useful starting position, but it gets you in all kinds of knots when trying to understand more complicated systems. A better picture is something like "(inertial) mass is a measure of the response of a system to an external force". So, for example, if you apply a force of one Newton to a system, and measure its acceleration to be one metre per second squared, then you can say that the system has a mass of one kilogram. But maybe if you took that system apart, applied the same force to the individual pieces, and summed the resulting mass that way, you'd get a different answer. There's no contradiction here because you are looking at two fundamentally different set-ups, so why *should* they have the same properties? Although you'd hope that they are related to each other, it would be almost more of a surprise, and certainly more boring, if the mass of a system were purely the sum of its individual parts.
This whole leap in understanding is particularly relevant for quarks and other particles, because the interactions there are that much more dramatic and relevant. As beso points out, most of the "mass" of a proton comes not from the quarks inside it, but from the binding energy between them. Again forgetting about the charm quark for a minute, the sum of the two up and one down quark masses is barely 10 MeV, when in the same units the proton mass is about 940 MeV. In terms of trying to predict the mass of protons, it barely matters whether you give the quarks inside them a mass or not.
There's no sense in my pretending this isn't weird. I hope I can try and explain even more what's going on over time.
The key concept to get a handle of, though, is that "mass" is not really (or at least not exclusively) a measure of the amount of stuff. It's a useful starting position, but it gets you in all kinds of knots when trying to understand more complicated systems. A better picture is something like "(inertial) mass is a measure of the response of a system to an external force". So, for example, if you apply a force of one Newton to a system, and measure its acceleration to be one metre per second squared, then you can say that the system has a mass of one kilogram. But maybe if you took that system apart, applied the same force to the individual pieces, and summed the resulting mass that way, you'd get a different answer. There's no contradiction here because you are looking at two fundamentally different set-ups, so why *should* they have the same properties? Although you'd hope that they are related to each other, it would be almost more of a surprise, and certainly more boring, if the mass of a system were purely the sum of its individual parts.
This whole leap in understanding is particularly relevant for quarks and other particles, because the interactions there are that much more dramatic and relevant. As beso points out, most of the "mass" of a proton comes not from the quarks inside it, but from the binding energy between them. Again forgetting about the charm quark for a minute, the sum of the two up and one down quark masses is barely 10 MeV, when in the same units the proton mass is about 940 MeV. In terms of trying to predict the mass of protons, it barely matters whether you give the quarks inside them a mass or not.
There's no sense in my pretending this isn't weird. I hope I can try and explain even more what's going on over time.
So Jim, can you check my analogy here. If we have 2x1 Kilo magnets stuck together and the force to pull them apart is say 10 kilos, is it fair to say that the actual mass is 12kg including the magnetic force, when if put on the scales it would only weigh 2kg? Is that analogous with the nuclear force between the particles the protons above?
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