https://doi.org/10.1140/epjp/s13360-024-05301-0
Regular Article
Mass and width of an unstable particle
Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, 61801, Urbana, IL, USA
Received:
16
February
2024
Accepted:
21
May
2024
Published online:
14
June
2024
We show that the mass and width of an unstable particle are precisely defined by the pole in the complex energy plane, 
, 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.
© The Author(s) 2024
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