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11 months ago in Particle Physics , Physics By Shahruddin Jafri

What Is Rest Mass in Particle Physics?

The E=mc² relation is clear, but in the Higgs era, I find the deeper ontology confusing. For a composite particle like a proton, where the constituent quarks have very small masses, how do we conceptually and rigorously define what the "rest mass" really represents?

 

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By Preetham M Answered 4 months ago

I recommend thinking of it as the invariant energy content of a system at rest. For an electron, most of its rest mass comes from its coupling to the Higgs field. But for a proton, which I've studied in QCD, the story is different. The Higgs mass of its quarks contributes only ~1%. The remaining 99% is the binding energy the kinetic and potential energy of the quarks and gluons confined within it. So, rest mass is fundamentally the measure of a system's total internal energy.

 

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