B Quarks and Antiquarks in a baryon

[Anthony Beckwith]

TL;DR Summary

Quarks and Antiquarks in a baryon. Pre-apologise for the novice question.

If Quarks and Antiquarks are bound together and don't appear individually why does baryon have 3 quarks but no antiquarks?

Again apologies if this is obvious and or novice.

Thanks
Anthony

 

[PeterDonis]

If Quarks and Antiquarks are bound together and don't appear individually why does baryon have 3 quarks but no antiquarks?

Because a bound state of a quark and antiquark is called a "meson", not a "baryon". (Note that you can also have an antibaryon with 3 antiquarks.)

A better question would be why those particular bound states are the ones that exist. The reason for that is that individual quarks have what is called "color", which is something like an electric charge but with three possible values (and three corresponding "anticolors") instead of one, but any bound state we actually observe has to be colorless, i.e., the colors of the individual quarks have to cancel each other out in the bound state. There are two ways the colors in a bound state can cancel:

(1) Have a quark with a particular color (red, green, or blue--those are the names for the three possible colors), and an antiquark with its corresponding anticolor (antired, antigreen, or antiblue), so the color and anticolor cancel out. This is a meson.

(2) Have three quarks, each with one of the three colors (red, green, and blue), which then combine to make "white", which is the same as being colorless and the colors canceling out (the detailed reason for why this can happen would go well beyond the scope of a "B" level thread, but it's been well confirmed experimentally). This is a baryon. (And you can also have an antibaryon with three antiquarks, each with one of the anticolors, that combine to make antiwhite, which is the same as being colorless.)

 

[phyzguy]

If Quarks and Antiquarks are bound together and don't appear individually why does baryon have 3 quarks but no antiquarks?

It's not true that "Quarks and Antiquarks are bound together and don't appear individually" What is true is that quarks are bound into assemblies that do not carry color charge. These assemblies are commonly referred to as "white". There are basically two ways to accomplish this. One is an assembly with one quark and on anti-quark with the opposite color (a red quark and an anti-red anti-quark, for example). These assemblies are called "mesons". The second way is an assembly of three quarks, one of each color (one red, one blue, one green). this assembly is called a "baryon". Of course, you can also have an assembly of three anti-quarks, one of each color (one anti-red, one anti-blue, one anti-green). This would also be called a baryon (or an anti-baryon if you prefer).

Looks like PeterDonis beat me to it!

 

[Anthony Beckwith]

thank you Peter and phyzguy, The article i was reading was worded a little misleading. thank you :)

 

[phyzguy]

I found this picture from Wikipedia to be helpful. This shows the color charges in the complex plane. From this you can see why red+blue+green=antired+antiblue+antigreen = 0.

 

[Anthony Beckwith]

Thank you both, It was my mistake I had misread the text in the study material. In my defence, I do have dyslexia. I have pasted the text below. I had understood it as a quark and antiquark must always be bound together obviously that is not the case.

Study material text:
"Quarks and antiquarks have never been observed in isolation; they only occur bound together inside hadrons.There are three confirmed recipes for building hadrons from quarks."