I need to calculate the lifetime of the W boson given its decay width. From what I know the lifetime of a particle is calculated by dividing $\hbar$ with the decay width $\Gamma$. From my textbook $\Gamma=2.141 $ GeV, and $\hbar=6.852 \times10^{-15} $Gev$\cdot$s, doing the lifetime calculation with these values gives me:


I know the correct solution is $3.2\times10^{-25}s$, but I can't for the life of me figure out how to get that number. What am I missing here?

  • $\begingroup$ Which unit has $\hbar=6.852 \times10^{-15}$? eVs, or GeVs, or something else? $\endgroup$ Jun 13, 2019 at 17:23
  • $\begingroup$ @ThomasFritsch I apologize, the units are Gev$\cdot$s. I have edited my post. $\endgroup$
    – matryoshka
    Jun 13, 2019 at 17:26
  • $\begingroup$ Look at Wikipedia:Planck constant. They have $\hbar = 6.582 \cdot 10^{-16}$ eVs. (i.e. without G) $\endgroup$ Jun 13, 2019 at 17:31
  • 2
    $\begingroup$ You seem to have done an incorrect conversion from $eV$ to $GeV$ as $\hbar = 6.582\times 10^{-16}eV \cdot s$, and $1 \; eV = 10^{-9}\; GeV$ $\endgroup$
    – Triatticus
    Jun 13, 2019 at 17:31
  • $\begingroup$ The Google calculator says hbar/(2.141 GeV) is $3.07432018\times 10^{-25}$ seconds. $\endgroup$
    – PM 2Ring
    Jun 13, 2019 at 17:34

1 Answer 1


You might want to check that value for $\hbar$ carefully.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.