- #1
Safinaz
- 259
- 8
Hi there,
In a reference as 1303.5877v1 [hep-ph ] the SM branching ratio of ## B \to \tau \nu ## is given by:
## \frac{m_B G_F^2 m_\tau^2 \tau_B f^2_B } { 8 \pi } V_{ub}^2 ( 1 - \frac{m_\tau^2}{m_B^2} )^2 ## . In the SM model the value of this BR ## \sim 0.7 \times 10^{-4} ## .
But I don't understand how the BR is of order 10^-4, while the mean life time ## \tau_B \sim 10^{-12} s ## and the Fermi constant ## \sim 10^{-5} GeV ^{ -2} ## ?
In a reference as 1303.5877v1 [hep-ph ] the SM branching ratio of ## B \to \tau \nu ## is given by:
## \frac{m_B G_F^2 m_\tau^2 \tau_B f^2_B } { 8 \pi } V_{ub}^2 ( 1 - \frac{m_\tau^2}{m_B^2} )^2 ## . In the SM model the value of this BR ## \sim 0.7 \times 10^{-4} ## .
But I don't understand how the BR is of order 10^-4, while the mean life time ## \tau_B \sim 10^{-12} s ## and the Fermi constant ## \sim 10^{-5} GeV ^{ -2} ## ?
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