If a neutron has two down quarks and one up, and a proton two up and one down, what happens when the neutron-?

Question

emits an electron to become a proton? Do the quarks somehow change their charge?

Answer 1

Firs of all, to become a proton, a neutron emits an electron *and* an a neutrino. It is called beta decay. To answer your question, first you have to understand why protons and neutrons has different charges. As you said, neutron has two down quarks and one up, and a proton two up and one down. Why one combination of quarks is electrically charged and the other not? Well, quarks have fractional electric charge, either Q = +2/3 or Q = −1/3. Now it is easy to understand. A proton has positive charge (2/3 + 2/3 - 1/3) and a neutron has zero charge ( 2/3 - 1/3 - 1/3).

"At the fundamental level (as depicted in the Feynman diagram below), this is due to the conversion of a down quark to an up quark by emission of a W- boson; the W- boson subsequently decays into an electron and an anti-neutrino." (http://en.wikipedia.org/wiki/Beta_decay)

Check references for further information.

Answer 2

Very interesting question. You could get a Nobel Prize for figuring this out. What you are describing is a change of flavor in the Standard Model Quarks via the Weak Force. Anybody who tells you they know how this all works is either lying or a deluded fool. This quark model is just the best theory they have figured out so far.
All quarks have "color" which is outside the scope of your question, and "flavor." The up have +2/3 charge, while down have -1/3 charge.
The flavors are up, down, bottom, top, strange, and charm. Nobody has seen any free quarks, so they can only exist, as far as we know, in pairs, or triples.

My guess on how all this works is that because no one has ever seen a proton decay, there is some mechanism that causes the second down quark to become an up quark (by emitting the electron) and now it is in a super-stable form that is the lowest energy level possible. In other words, it must take energy away from the proton for it to decay, otherwise it would.
But how does it manage to lump together enough bits to have a -1 charge, from "stuff" that is in 2/3 and 1/3 lumps...that is interesting too

Answer 3

No, just one of the down quarks converts to an up quark. The difference in charge is just the charge of an electron. In addition an electron-anti-neutrino is emitted.