I know that a proton consists of two up quarks and a down, but recently I was reading that anti-quarks just burst into the scene and pair with their associated partner. What I'm wondering is, how can this happen, and the mass of the proton remain constant?

That comma isn't meant to be there.

You are wondering why the quarks in nucleons are not just annihilated by anti-quarks generated spontaneously by pair production?

I know that a proton consists of two up quarks and a down, but recently I was reading that anti-quarks just burst into the scene and pair with their associated partner. What I'm wondering is, how can this happen, and the mass of the proton remain constant?

That comma isn't meant to be there.

Protons are spin-½ fermions and are composed of three valence quarks,^[3] making them baryons (a sub-type of hadrons). The two up quarks and one down quark of the proton are held together by the strong force, mediated by gluons.^[4]:21–22A modern perspective has the proton composed of the valence quarks (up, up, down), the gluons, and transitory pairs of sea quarks.

 

Above is from wikipedia http://en.wikipedia.org/wiki/Proton

 

The "sea quarks" are what you are referring to.

I know that a proton consists of two up quarks and a down, but recently I was reading that anti-quarks just burst into the scene and pair with their associated partner.

 

Where were you reading this?

You are wondering why the quarks in nucleons are not just annihilated by anti-quarks generated spontaneously by pair production?

 

ajb, I am wondering your question, though this seems to be off-topic if OP does not mean this is his question. Can you help answer this question?

ajb, I am wondering your question, though this seems to be off-topic if OP does not mean this is his question. Can you help answer this question?

 

I don't know the answer - but if you have spontaneous PAIR production and one quark annihilates with its anti-quark then you should still have the correct number of quarks.

 

ie you have 2 ups and a down; thru spontaneous pair production you get an up and an anti-up. the anti up annihilates with one of the original ups and you are left with 2 ups and a down.

 

Whether this actually happens (I am unsure of the reality all stages) and whether it accounts for spin etc - the maths of the quarks is ok

ie you have 2 ups and a down; thru spontaneous pair production you get an up and an anti-up. the anti up annihilates with one of the original ups and you are left with 2 ups and a down.

 

May I know why you can get an up and an anti-up through spotaneous pair production but not any possible number if the PAIR can borrow enough energy from the vacuum?

 

May I know why you can get an up and an anti-up through spotaneous pair production but not any possible number if the PAIR can borrow enough energy from the vacuum?

 

It can "borrow energy" but it cannot manufacture charge - so you get the same number of +ves as -ves, ie you get a particle and an antiparticle

No, sorry I can`t get your meaning. Manufacture charge? I thought it did create something out of nothing. Get the same number of positives and negatives? What/which positives and negatives? The PAIR? I mean say you have 2 ups and 1 down-1 proton. If a PAIR exist, why should it be 1 up and 1 anti-up but not 2 up and 2 anti-up or 3 up and 1 anti-up or any possible numbers/figures? And if 1 up and 1 anti-up exist should they cancel out each other or the exist-from-nothing anti-up would annihilate one of the existed-up(the original up in the proton) and thus the exist-from-nothing up would take over the annihilated up, taking over its place, considering itself as the new up out of the 2 ups in the proton?

Edited September 10, 201411 yr by Nicholas Kang

No, sorry I can`t get your meaning. Manufacture charge? I thought it did create something out of nothing. Get the same number of positives and negatives? What/which positives and negatives? The PAIR? I mean say you have 2 ups and 1 down-1 proton. If a PAIR exist, why should it be 1 up and 1 anti-up but not 2 up and 2 anti-up or 3 up and 1 anti-up or any possible numbers/figures? And if 1 up and 1 anti-up exist should they cancel out each other or the exist-from-nothing anti-up would annihilate one of the existed-up(the original up in the proton) and thus the exist-from-nothing up would take over the annihilated up, taking over its place, considering itself as the new up out of the 2 ups in the proton?

 

Spontaneous pair production can happen - but we have to have conservation of charge, that is to say that the pair will always consist of one positive charged and one negative - a particle and its antiparticle. An up quark has +2/3 electrical charge and an anti-up quark has an electrical charge of -2/3 - so if you produced them spontaneously in open space you go from net charge zero (0 - there is nothing there ) to net charge zero (-2/3 + 2/3 =0 ).

 

And I agree with your last sentence; it is what I was hinting at. BUT - spontaneous pair production of quarks is not something I know about especially within the confines of a proton. It may work out mathematically when looking just at the sum of the charges - but there are numerous other reasons why this may or may not happen.

 

http://en.wikipedia.org/wiki/Pair_production

 

This wikipage describes the phenomenon I would suggest a read, it is fascinating and you will see the basis of this phenomenon on conservation. Note that it never explicitly mentions quarks although it does mention strangeness which I think only applies when dealing with strange quarks so the possibility of quark production is implied. Quark production would involve both qed and qcd and is so far above my paygrade that I will be reprimanded for even mentioning it.

Spontaneous pair production can happen - but we have to have conservation of charge, that is to say that the pair will always consist of one positive charged and one negative - a particle and its antiparticle. An up quark has +2/3 electrical charge and an anti-up quark has an electrical charge of -2/3 - so if you produced them spontaneously in open space you go from net charge zero (0 - there is nothing there ) to net charge zero (-2/3 + 2/3 =0 ).

 

So why not 2 ups and 2 anti-ups, 2 ups and 3 anti-ups, 4 ups and 4 anti-ups exist instead of 1 up and 1 anti-ups exist? Is this impossible because it hasn`t exceed the total rest mass energy of the 2 particles?

No, sorry I can`t get your meaning. Manufacture charge? I thought it did create something out of nothing. Get the same number of positives and negatives? What/which positives and negatives? The PAIR? I mean say you have 2 ups and 1 down-1 proton. If a PAIR exist, why should it be 1 up and 1 anti-up but not 2 up and 2 anti-up or 3 up and 1 anti-up or any possible numbers/figures?

 

3 up and 1 anti-up is not a possible number, since it violates conservation of charge. There's no way around that conservation law in this scenario.

Oh, swansont imatfaal had explained that to me. Now, may I ask you the question the same as imatfaal as in post number 11?

Edited September 10, 201411 yr by Nicholas Kang

Those are possible. It doesn't change the answer, though — after everything annihilates, you're still left with a proton's complement of quarks.

And what about the second question in post number 10, which imatfaal himself also doesn`t know the answer?

 

Edited September 10, 201411 yr by Nicholas Kang

Other than some superficial points, QCD is well out of my comfort zone.

Ah, I thought you are Dr. swansont in physics. May I know which field are you specialized in? So, next time I can direct the correct question to the correct people. Sorry for asking things that aren`t your in your comfort zone. And thanks for answering the previous question.

spontaneous?There has to be an input of energy.

Ah, I thought you are Dr. swansont in physics. May I know which field are you specialized in?

 

Atomic physics.