Fermi coupling constant

1. Nov 17, 2012

rioo

i'm reading through halzen and martin's chapter 12 on the weak interaction which they calculate the fermi coupling constant form oxygen beta decay using
$\Gamma = 1/\tau = G^2E_0^5/30\pi^3$
with $E_0 = 1.81$MeV and $\tau log 2 = 71$ sec. they get $G\approx 10^{-5}/m^2_N$. where m_N is the nucleon mass.
i cant reproduce this number, just plugging in is way off. are there factors of c or h that i need to include?

2. Nov 18, 2012

Einj

Actually, to have the right dimension, is $\Gamma=\hbar/\tau$. If you plug all the numbers considering that the calculation gives the correct answer.

3. Nov 18, 2012

rioo

yes it does thanks. natural units are annoying

4. Nov 20, 2012

Meir Achuz

You can use the conversion constant 1=192.33 MeV-fm

5. Nov 20, 2012

Bill_K

Close. ħc = 197.326 MeV-fm.

(Much more useful than whatever it is in Joule-m! )