How many quarks in a proton?

[Curious layman]

Wiki says two up, one down.

Just read this on Quora.

Quote

You may have heard that a proton is made from three quarks. Indeed here are several pages that say so. This is a lie — a white lie, but a big one. In fact there are zillions of gluons, antiquarks, and quarks in a proton. The standard shorthand, “the proton is made from two up quarks and one down quark”, is really a statement that the proton has two more up quarks than up antiquarks, and one more down quark than down antiquarks. To make the glib shorthand correct you need to add the phrase “plus zillions of gluons and zillions of quark-antiquark pairs.” Without this phrase, one’s view of the proton is so simplistic that it is not possible to understand the LHC at all.

Which is true?

https://qr.ae/pNe457

 

 

Edited December 11, 2020 by Curious layman

[swansont]

Particles are counted as a positive number , and antiparticles as a negative. So a particle/antiparticle pair has a particle number of zero. It's bookkeeping.

Thus the statement that there are three quarks is true. The number of gluons is immaterial, as it was not part of the question, and the number of quark/antiquark pairs (mesons) is immaterial as well, as their quark number is zero.

This bit:

“plus zillions of gluons and zillions of quark-antiquark pairs.” Without this phrase, one’s view of the proton is so simplistic that it is not possible to understand the LHC at all.

Is accurate, because physics is more than memorization of a few facts. Saying that a proton is comprised of two up quarks and one down quark is not meant to be a comprehensive description of a proton, or what happens at the LHC. The gluons and mesons are important in understanding the interactions that go on within a proton, so the quora blurb is addressing a different question than what was asked.

[timo]

The quoted part of the text you provided seems correct to me. In particle physics, there is a concept of a parton. A parton is the thing that does the core interaction when a proton is shot at something else in a particle collider ("core interaction" is the part of the process with the highest energy, the one that you draw Feynman diagrams for to describe it). Experimental physicists have a very pragmatic approach to these partons: They define a probability to get a certain parton (a  quark or a gluon) with a given momentum from the proton. These probabilities can be taken into account when simulating/calculating collider events. The probability function is called the parton distribution function (PDF). These PDF can be measured in experiments, and they also contain heavier quarks. Just Google for them yourself, the first hit I found (no guarantee for quality) is figure 1 of http://www.scholarpedia.org/article/Introduction_to_Parton_Distribution_Functions.

So from the perspective of someone doing particle physics experiments, it is probably correct to say that a proton contains all kinds of stuff. There are a lot of reasons I can think of why that could be missing the big picture (is this an effect of perturbation theory? How is the probability  to heavier quarks related to the CKM matrix? How is the remnant of the interaction, the Underlying Event, handled? ...) but I lack both time and skill to write about this.

 

Bottom line: Saying that a proton is more complicated than three quarks held together by a gluon pit is correct. There is at least one mathematical model that describes it as a magical box containing random objects which may well be the most-used mathematical proton model in the world. I agree with the author that specifically to understand LHC physics, "it is three quarks" is not enough. I don't think that "plus zillions of gluons and  quark, anti-quark pairs" is the key to enlightenment, either.

[MigL]

On top of the expert opinions above, I will add my two cents ...

The modern picture of a fundamental quantum particle is a point surrounded by a cloud of virtual particles, which grow more and more massive/energetic as you reduce separation. These 'extra' particles add to mass, charge, etc. of fundamental particles, and is their 'effects' that are stripped away in the renormalization of any QFT.

A proton is not fundamental, but is composed of quarks, which are; and the quarks are in close proximity.
The way Physicist 'dismantle' a proton, is by smashing it at high energies against another particle, and seeing what 'comes out'.
High energy protons collisions produce quite a few particles.

Even at its lowest energy, a proton is over 98% binding energy; this energy alone is enough to 'produce' a couple of hundred quark/ anti-quark pairs.
And there have been scattering experiments done which confirm that a proton acts like a 'bag' full of particles.
( not zillions and zillions )
 

[Alan Conrad]

In Lisa Randall's book Knocking on Heaven's Door, which is primarily about the LHC,  she refers to "the sea of quarks" inside a proton. She is obviously not talking about "three up quarks and two down quarks".

[joigus]

7 hours ago, Alan Conrad said:

In Lisa Randall's book Knocking on Heaven's Door, which is primarily about the LHC,  she refers to "the sea of quarks" inside a proton. She is obviously not talking about "three up quarks and two down quarks".

It's two up and one down.

https://en.wikipedia.org/wiki/Proton

Plus gluons dancing around telling the quarks and each other to change colour, plus a number of virtual quark-antiquark and gluon states. That soup is what Lisa Randall refers to as "the sea".

[wtf]

I happened to run across this terrific talk called The Secret Life of Quarks, well worth watching.

https://www.youtube.com/watch?v=H_PmmMkGyx0

Like others, I'd always heard there are 3 quarks inside the proton. Turns out it's not really true. 3 is the number of quarks minus the number of antiquarks. But it's not a matter of counting and subtracting. Rather, you integrate something called the quark density function, and when you do, you get the answer of 3. The actual number of quarks and antiquarks depends on the scale at which you look. So there could be millions, zillions, whatever. I'm fuzzy on that part.

But it's not 3 as in the counting number 3. 3 is what you get by integrating the quark density function, and it's much more complicated than just subtracting one integer from another. I found this article too, which I didn't read much of but that bears on the matter.

https://en.wikipedia.org/wiki/Parton_(particle_physics)

I'm curious about getting an amateur-level understanding of this answer myself. I'd always heard 3, but that's apparently a tremendous simplification that's not literally true.

The other really interesting thing about all this (probably old hat to the pros in here), which I also learned recently from Youtube, is that mass comes from the binding energy among the quarks inside the nucleus. It takes a huge amount of energy to pull quarks apart, which is why you never see them in isolation. By Einstein's famous [math]E = mc^2[/math], that energy turns into mass. That's actually where mass comes from. Now the question is, why does the binding energy of the quarks in the nucleus bend spacetime? A Nobel awaits whoever figures that one out.

Edited March 24, 2021 by wtf

[Sensei]

On 3/9/2021 at 5:08 AM, Alan Conrad said:

In Lisa Randall's book Knocking on Heaven's Door, which is primarily about the LHC,  she refers to "the sea of quarks" inside a proton. She is obviously not talking about "three up quarks and two down quarks".

What is missing, but a key essential element (including this thread), in the Standard Quark Model there are "valence quarks" i.e. those that contribute to the total Baryon Number, and other quantum numbers, and those that are not valence quarks (they cancel out their quantum numbers with their antiparticles).

https://en.wikipedia.org/wiki/Quark_model

Some people/scientists simply skip word "valence", taking it as granted, while talking about "the number of quarks in composite particle".

[swansont]

The lesson here is that all of physics is approximation. There's always more to it when you dive deeper into any topic.

[studiot]

1 hour ago, swansont said:

The lesson here is that all of physics is approximation. There's always more to it when you dive deeper into any topic.

Hear, Hear; waves Physics order papers and claps.  +1