Mass and width of an unstable particle
Abstract
We show that the mass and width of an unstable particle are precisely defined by the pole in the complex energy plane, μ = m - (i/2), by identifying the width, , with the particle's decay rate and the mass, m, with the oscillatory frequency. We find that the physical Z boson mass lies 26 MeV below its quoted value, while the physical W boson mass lies 20 MeV below. We also clarify the various Breit-Wigner formulae that are used to describe a resonance.
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