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Homework Help: Particle decay and relativity

  1. Apr 12, 2008 #1
    1. The problem statement, all variables and given/known data

    A particle with mass M decays into 2 particles of equal mass m.

    1: Calculate the speed of the decay particles

    2: Concider the case ρ->[tex]\Pi\Pi[/tex]: M = 770 MeV and m[tex]\Pi[/tex]= 140 MeV

    2. Relevant equations

    m = [tex]\gamma[/tex]m(restmass) ?

    3. The attempt at a solution

    I suppose M/2 is restmass and found an expression for the speed. However since the mass increase when the speed approaches the speed of light, this would imply that m is a larger number than M/2. But in task 2, it says M/2 is larger than m[tex]\Pi[/tex], which implies i've done something wrong.

    Please help me solve this task or find out what i did wrong.
  2. jcsd
  3. Apr 12, 2008 #2


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    Gold Member

    The question is ambiguous since you don't say in what frame the calculation is done. I assume in the rest frame of the decaying particle? Then the eenrgy of each produced particle is M/2 and this is equal to [tex] \gamma m c^2 [/tex] where m is the mass of each produced particle.
  4. Apr 12, 2008 #3
    Ok now i understand it, thank you for the answer. :)
    Last edited: Apr 12, 2008
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