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How much heavier would the proton be with respect to the neutron if the up quark and the down quark had the same mass? How much does the electric field energy density of the proton contribute to its mass?

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  • $\begingroup$ It's complicated: Pagels 1966. $\endgroup$ – Cosmas Zachos Nov 27 '17 at 22:35
  • $\begingroup$ West 1980. The current quarks' masses themselves differ by 2.5MeV, however.... $\endgroup$ – Cosmas Zachos Nov 27 '17 at 22:57
  • $\begingroup$ Let me mention arXiv:1406.4088 to add a slightly more recent discussion. While the first line of Table 1 provides a numerical answer to these questions (reporting that the d-u quark mass difference provides ~2.5MeV to the neutron--proton mass difference while electromagnetism provides ~-1MeV, both with ~10% uncertainties), this result relies on specifying a convention for separating the electromagnetic and quark-mass contributions, discussed further in Section 10.3 of the Supplementary Material. $\endgroup$ – David Schaich Nov 28 '17 at 15:56

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