Specifically, why is the neutron heavier than the proton?

In summary, the proton is made up of 2 up quarks and 1 down quark, while the neutron is made up of 2 down quarks and 1 up quark. The mass difference between the two particles is due to a combination of factors, including the different masses of the up and down quarks, the interactions/dynamics inside the particle, and the differences in electric charge of the quarks. These factors are complex and require numerical calculations. Some theories suggest that the different coupling of up and down quarks to the omega meson field is the main cause of the mass difference. However, some argue that the anthropic principle, which states that the universe must be compatible with the existence of observers, could also
  • #1
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Proton is made of 2 up, 1 down quarks
Neutron is made of 2 down, 1 up quarks

The up and down quark have different masses, which account for some of the mass difference. I've also read that hadron masses depend upon the interactions/dynamics inside the particle, not just the quarks contained.

What types of interactions/dynamics have an influence on the mass and result in the neutron being heavier than the proton?
 
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  • #2
These two papers 1 2 seem to say that it's the different coupling of up and down quarks to the omega meson field, that is most responsible for the mass difference. But I have not actually worked through them.
 
  • #3
About 60% of the mass difference is due to the quark mass difference, and about 40% from the differences in electric charge of the quarks - you can view this as a proton having more internal repulsion than the neutron, which in turn changes the wavefunction slightly. These calculations are complex and need to be done numerically. Also, I believe the two effects are in opposite directions.
 
  • #4
Anthropic principle. Otherwise there would be no universe.
 
  • #5
I don't like the anthropic answer.
  1. I feel it is an argument of last resort, and in this case we don't need it.
  2. It's not necessarily true - the universe might have turned out differently and the denizens of that putative universe might be wondering why it had to turn out differently.
  3. I don't think it's true in this case. If the proton were a little lighter than the neutron, the proton would still be stable or observationally stable. BBN would be all screwed up, but I don't think it would make a difference to what we are made out of.
 

1. Why is the neutron heavier than the proton?

The neutron is heavier than the proton because it contains one additional fundamental particle called a "down" quark, which has a larger mass than the "up" quark found in the proton.

2. How do we know that the neutron is heavier than the proton?

Scientists have conducted numerous experiments, such as scattering experiments and mass spectrometry, to determine the mass of particles. These experiments consistently show that the neutron is slightly heavier than the proton.

3. Are there any other factors that contribute to the neutron's heavier mass?

Yes, there are other factors that contribute to the neutron's heavier mass, such as the internal energy of the particles and the mass difference between the "up" and "down" quarks.

4. Is the mass difference between the neutron and proton significant?

Yes, the mass difference between the neutron and proton is significant in terms of atomic and nuclear processes. This slight difference in mass can have a big impact on the stability and behavior of atoms and their nuclei.

5. Could the mass difference between the neutron and proton be due to measurement error?

No, the mass difference between the neutron and proton has been confirmed by multiple experiments and is considered a well-established fact in physics. Any measurement error would be too small to account for the observed difference in mass.

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