Charge Conservation in Neutron Decay

In summary, the conversation discusses the decay of a neutron into a proton, positron, and neutrino. It is explained that a proton is made up of two up quarks and a down quark, while a neutron is made up of one up quark and two down quarks. The charges of these particles are also mentioned, with an up quark having a charge of +2/3 and a down quark having a charge of -1/3. The question is then raised about how the charge is conserved and divided in the decay of a neutron. It is pointed out that the hypothetical decay proposed by the questioner violates the conservation of charge, and the correct decay channel is neutron to proton plus electron plus anti
  • #1
Kestrel
5
0
A neutron can decay into a proton, a positron, and a neutrino.
A proton is made up of two up quarks and a down quark.
A neutron is made up of one up quark and two down quarks.
An up quark has a charge of +2/3, and a down quark has a charge of -1/3.

Given the statements above, can someone please explain how the charge is conserved and/or divided in the decay of a neutron? You start with three particles, two of which have a charge of -1/3 (down) and one of which has a charge of +2/3 (up). Then it decays, and you end up with 5 particles, one which has charge of -1/3 (down), two with charge of +2/3 (up), one with charge of +1 (the positron), and a neutral neutrino.

Charge is conserved, but where exactly does it get broken up? If you write it in equation form, you can cancel one up and one down quark from each side and end up with an up quark decaying to a down quark, a positron, and a neutrino. Is this indeed what happens? An up quark, with charge +2/3, loses 1 unit of charge (dropping to a -1/3), and in the process produces some extra particles? This would imply each up quark containing a positron, which, while I could be wrong, doesn't sound right.

Any and all clarification would be appreciated, thank you!

Scott
 
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  • #2
Charge is explicitly not conserved in your hypothetical decay! You have a neutron with charge 0 going to a proton and a positron with total charge of +2. Conservation of charge is violated and the decay cannot occur. The correct decay channel is neutron to proton plus electron plus anti-neutrino. See here for more: http://hyperphysics.phy-astr.gsu.edu/HBASE/particles/proton.html

Hope this helps.
 
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  • #3
Wow! My mistake, that was a big error. Sorry about that! What I meant to ask was, in the decay of a neutron (as you point out to be correctly "neutron to proton plus electron plus anti-neutrino"), how does the charge get broken up?

u + d + d ---> u + u + d + e + antineutrino

Basically what I'm asking is, how is it that you end up with an integral charge when all you start with is fractional charges? We're dealing with leptons here. I understand that charge is conserved, but it is rearranged. Do we understand the process by which this happens? Going from the equation above, you could "cancel" the "spectators" (forgive the chemistry terminology) and end up with

d ---> u + e + antineutrino

(-1/3) ---> (+2/3) + (-1) + (0)

It appears that a down quark contains an up quark, an electron, and an antineutrino, but the extra particles could be a result of something else.

Thanks again!

Scott
 
  • #4
Down quark does not "contain" an up quark plus electron, anymore than an up quark "contains" a down quark plus positron (nucleus with excess protons leads to psitron emission). These changes are transformations, not decompositions.
 
  • #5
So what is the mechanism of the transformation? Or is it one of those things we just say "happens?"

Scott
 
  • #6
The decay changes the flavor of the quarks so it must be a weak decay. The lowest order Feynman diagram corresponds to a down quark decaying into a [tex]W^-[/tex] and an up quark. The [tex]W^-[/tex] then decays into an electron and an anti-neutrino.
 
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  • #7
Excellent! Thank you mathman and Physics Monkey, that was exactly what I was looking for!

I just found it odd that you could get integral charges from fractional charges, but the W boson (after some research) has cleared this up. I still find it a little odd (just as I find .999... = 1 odd), but this certainly clears a lot up.

Thanks again!

Scott
 
  • #8
An explicit discussion on this specific matter, including calculations is found in Griffiths' introductory text on particle physics...

Daniel.
 

Related to Charge Conservation in Neutron Decay

1. What is charge conservation in neutron decay?

Charge conservation in neutron decay refers to the fundamental principle in physics that states that the total electric charge in a closed system remains constant. This means that the amount of positive charge must be equal to the amount of negative charge in any given system.

2. How does charge conservation apply to neutron decay?

In neutron decay, a neutron (which has no electric charge) decays into a proton (which has a positive charge) and an electron (which has a negative charge). In order to conserve charge, the total charge of the products (proton and electron) must be equal to the charge of the initial neutron. Therefore, the electron carries away the negative charge and the proton carries the positive charge, ensuring that the total charge remains constant.

3. Why is charge conservation important in neutron decay?

Charge conservation is important in neutron decay (and in all other physical processes) because it is a fundamental law of nature. It helps explain why certain physical processes occur and why they occur in a certain way. It also plays a crucial role in understanding the behavior of subatomic particles and the structure of matter.

4. Is charge conservation always observed in neutron decay?

Yes, charge conservation has been experimentally observed in all known cases of neutron decay. This provides strong evidence that charge is a conserved quantity in nature.

5. How does charge conservation relate to other conservation laws?

Charge conservation is closely related to other conservation laws, such as energy conservation and momentum conservation. These laws all stem from the same fundamental principle that physical quantities cannot be created or destroyed, but can only be transformed or transferred from one form to another.

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