Why can't a neutron be thought of as a proton plus an electron and neutrino?

In summary: The neutrinos have zero charge. The anti-electron-neutrino has a negative charge, the anti-muon-neutrino has a neutral charge, and the anti-tau-neutrino has a positive charge.
  • #71
First of all, reply to turin;

A meson and a baryon will each be color-white, and hence no direct strong force attraction between them if they happen to separate slightly. The moment the meson is emitted, its constituent quarks fall outside of the range of free gluons from the baryon. Only the gluons between the constituents of the meson will affect the structure of the meson at that point, as far as strong potential is concerned.
The actual emmission of the meson is most likely just the reaction of a baryon to its close proximity to another baryon (like an electron emiting a photon in response to the proximity of another electron), or if decay is involved it is linked to the weak force rather than the strong force.
Thankyou to jcsd for elaborating on QFD as a QFT.

*I just saw your new message post, and you are totally correct about your last comment; the mesons do act very much in the same way between baryons as photons act between charged particles. I think you are beginning to get a clearer idea of the concept. Just one thing to keep in mind; the x^2 potential is between quarks within composite baryons and mesons, not between baryons and other baryons or mesons (and by the way, x^2 is only an educated approximation at this time, we do not know for sure the exact form).

Now, to NEOclassic;

jcsd is correct about the SM view of neutrinos. For one, if neutrinos and antineutrinos were self-conjugates, like photons, there would be a violation of lepton number conservation in many well-known interactions that follow the principle; that is, unless the lepton number of a neutrino can be arbitrarily assigned, and thus a neutrino of L = -1 and a neutrino of L = 1 can be produced as a pair(hence a reason for calling some neutrinos and some antineutrinos). This definition, however, would intrinsically define them as non-self-conjugate antiparticles, as electrons and positrons have opposite lepton numbers as well (in addition to opposite charge). If we consider electrons to have an isospin of -1/2 and a lepton number of -1, then their charge could be described as;

Q = I~3 + L/2

which equals one for the positron, -1 for the electron, if we are able to use the convention where the sign of L is the same as the sign of Q in charged leptons. The neutrinos, to conserve quantum numbers, must then be assigned the opposite isospins, so that Q = 0 for both neutrino and antineutrino. This puts neutrinos in isospin doublets with their associated leptons. This doublet form for the leptons is exactly how they are represented in the SM.
In conclusion, I would say that the opposite lepton numbers required for neutrinos and antineutrinos is sufficient to define them as not being self-conjugates, if the current SM is accurate with regard to the isospin doublet structure of quarks and leptons.
 
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  • #72
Spin, lads, spin

Long long time ago it was said that a nucleus was composed of protons and electrons. This was ruled out on spin arguments. Take for instance a 208 Pb 82, nucleus. It should have 208 protons and 126 electrons. The charge fits, but the angular momentum fails then.

Same, but more subtle, for the neutron=proton+electron+(anti)neutrino. In this view the freedom for neutron total angular momentum differs from the one of the proton, because the proton should be considered a single particle while the neutron should be seen as a sum of three.

With quarks, both proton and neutron are in equal footing.
 
  • #73


Originally posted by arivero
Long long time ago it was said that a nucleus was composed of protons and electrons. This was ruled out on spin arguments. Take for instance a 208 Pb 82, nucleus. It should have 208 protons and 126 electrons. The charge fits, but the angular momentum fails then.

Same, but more subtle, for the neutron=proton+electron+(anti)neutrino. In this view the freedom for neutron total angular momentum differs from the one of the proton, because the proton should be considered a single particle while the neutron should be seen as a sum of three.

With quarks, both proton and neutron are in equal footing.

Hi Arivero,
It seems to me that each paragraph of your post contains an inconsistency.
1. J.J. Thompson's plum-pudding applied to a whole atom - not a nucleus.
2. The total angular momentum (spin = 1/2) obtains for each nucleon.
3. Magnetically speaking, the proton and the neutron will never be on equal footing - neutron = -1.91 nuclear magnetons vs proton = +2.79 nm. Thanks for your audience. Cheers
 
  • #74
Before the neutrino was conjectured by Fermi, neutrons were often treated as protons with an added electron (a totally incorrect concept, but nobody knew better). If isospin symmetry was an exact symmetry, and if electric charge dissappeared, the proton and neutron would be on equal footing in every way; they would even become degenerate in mass. That is, the strong force could be taken to be an exact symmetry of nature, and up and down quarks would become degenerate. Remember that the nucleons fall in the ground state of baryonic resonances, thus the total spin j = 1/2 is due completely to spin momentum and not angular momentum (because N = 0, l = 0, according to Fermi-Dirac statistics). They also have an isospin I = 1/2, where the neutron and proton have opposite magnitudes of isospin.
 
  • #75


Originally posted by NEOclassic
Hi Arivero,
Hi neo,

1. J.J. Thompson's plum-pudding

Did I named Thomson? I was referring, as the other poster has already remarked, to a theory of the nucleus.

2. The total angular momentum (spin = 1/2) obtains for each nucleon.
Ok I have not been clear here. For the neutron=electron+proton, the spin issue fails completely. If you add the neutrino, it must be bound to the inside of the neutron, and you must assume that it is in the ground state, only with both conditions you can get the 1/2 of the neutron.
3. Magnetically speaking, the proton and the neutron will never be on equal footing

It is obvious I was referring to spin issues. I know that the proton has charge +1, too... was this the next argument?

The point is that in current theory both nucleons are composed of three spin 1/2 particles. In the theory proposed in this thread, the neutron would be composed of three spin 1/2 particles but the proton would be composed of a single particle.

Cheers

Alejandro
 

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