Advanced Physics Question (Quarks, masses)

Chop Logic

I'm studying for my physics final tomorrow and I just came across this question. Googling doesn't really help (kind of hard to google a question like this) and I can't find a clear answer anywhere in my textbook. Question is:

A proton consists of two up quarks and a down quark. Is the sum of the masses of two up quarks and a down quark equal to the mass of a proton? Explain.

I think the answer is just, yes, but that seems too simple for a question like this (the other questions are fairly complicated). If anyone could explain this to me I'd really appreciate it.

Thanks.

Fuzzywhale

hey so what level class is this?
I think the bare mass calculation is just two ups and and down. If we are being fancy then you need to talk about contributions from the gluon field, and other exciting things. does that help?

Edit: I'll add a disclaimer, I'm a string theorist so my real world calculations may be horrendously wrong/not even close

Junpei

Isn't it that the quarks themselves don't contribute much in the way of MeV, it's the quantum energy from the gloun field that constitutes most of it. Quarks by themselves only mass in at around 3-6 MeV each (downs are "heavier" if I remember correctly, but it's been a while). But as Fuzzy stated, it comes down to the level of physics you are doing. If you aren't dealing with gluon fields or quark movement then the answer basically is "Yes"

Demerdar

If a proton is made up of only those components, then yes.

Seol

Um, surely there's gonna be some potential energy associated with holding the proton together, which means the mass of the proton is going to be less than the combined mass of its constituent quarks (the PE will be zero at infinity, therefore negative when they're proximate)?

Disclaimer: I haven't done much quantum physics, just extrapolating from what I know. But regardless of the intricacies of string theory and gluon fields, if it takes energy to separate them, then there's negative energy holding them together, which in turn means reduced mass. Not a lot, but nothing's a lot at that scale.

physi_marc

Seol wrote: »

Um, surely there's gonna be some potential energy associated with holding the proton together, which means the mass of the proton is going to be less than the combined mass of its constituent quarks (the PE will be zero at infinity, therefore negative when they're proximate)?

Disclaimer: I haven't done much quantum physics, just extrapolating from what I know. But regardless of the intricacies of string theory and gluon fields, if it takes energy to separate them, then there's negative energy holding them together, which in turn means reduced mass. Not a lot, but nothing's a lot at that scale.

Particle physics is really not my thing at all (I'm in medical physics), but I would tend to agree with Seol. The proton mass should be less than the sum of the mass of the quarks since energy goes into binding the whole thing together.