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Pion decay in electron and neutrino

  1. Apr 25, 2009 #1
    I have a question about this decay: [tex]\pi^- \rightarrow e^- \overline{\nu_e}[/tex]
    there is a factor:

    [tex]1 - \frac{v_e}{c}[/tex]

    what are these values, [tex]v_e,c[/tex], and why this quantity is equal to:

    [tex]\frac{m^2_e}{m^2_\pi + m^2_e}[/tex]?

    Thank you
  2. jcsd
  3. Apr 25, 2009 #2
    Sorry but I don't understand why the latex don't work...

    the decay is

    pi- -> e- anti-nu(e)

    the factor is: 1-v/c

    and I don't understand what are v and c...
    and why that quantity is equal to: (m_e)^2 / [(m_pi)^2 + (m_e)^2]

    Thank you
  4. Apr 26, 2009 #3


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    Science Advisor

    v is the electron velocity and c the speed of light.
    In special relativity, v/c=pc/E, where p is the momentum and E the total energy.
    Some more algebra is required to get the final result.
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