# Where can I find experimental data

## Main Question or Discussion Point

Does anyone know where I can find experimental data on the life time of charged pion decay? More specifically the life time of a negatively charged pion decaying into either an electron and an electron neutrino or into a muon and a muon neutrino.

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fzero
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Does anyone know where I can find experimental data on the life time of charged pion decay? More specifically the life time of a negatively charged pion decaying into either an electron and an electron neutrino or into a muon and a muon neutrino.
The best place to start is at the Particle Data Group website at http://pdglive.lbl.gov Charged pion data, including lifetime and branching ratios, are at http://pdglive.lbl.gov/Rsummary.brl?nodein=S008&exp=Y&sub=Yr&return=MXXX005 [Broken] The section references are in a link at the top RHS of that page, as well as in the pdf that you can download by following the Particle Listings link on the main PDG page.

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How do I get the life-time for the decay from http://pdglive.lbl.gov/Rsummary.brl?...return=MXXX005? [Broken] All I could see was the probability for each type of decay and the mean life time for the pion.

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fzero
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The probability for each decay mode is expressed in terms of the branching ratio $$\Gamma_i/\Gamma$$, where $$\Gamma_i$$ is the partial decay rate for the specific process and

$$\Gamma = \sum_i \Gamma_i$$

is the total decay rate. The mean lifetime is $$\tau = 1/\Gamma$$.

It is possible to define a partial lifetime $$\tau_i = 1/\Gamma_i$$ for each decay mode. This doesn't really have the same significance as a mean lifetime, because all of the decay modes compete. So whereas we can define a total half-life

$$\tau_{1/2} = \tau \ln 2$$

as the time it takes for half of the pions in a sample to decay, a quantity like

$$\tau_{e^+\nu_e} \ln 2$$

doesn't really correspond to the time it takes for half of a sample of $$\pi^+$$ to decay to positrons, since over that period of time, most of the sample will have instead decayed to muons.