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Homework Help: Desintegration momentum

  1. Jan 17, 2014 #1
    1. The problem statement, all variables and given/known data

    Given the desintegration of one particle,

    1 -> 2 + 3

    then show that

    p1^2 = p2^2+p3² + 2cos(theta)*p2*p3

    p1: momentum particle to be desintegrated
    p2, p3: momentum of the two resulting particles
    theta: angle between 2 & 3

    2. Relevant equations

    3. The attempt at a solution

    I tried using conservation of quadrivector
  2. jcsd
  3. Jan 17, 2014 #2
    I am curious as to why you attempted this via 4-momentum? Is the text you are working with promote that use?

    Anyways, the way I would approach this is a lot simpler, you do not need 4-momentum. Think of this by looking at the conservation of momentum thus,


    and it follows that taking the inner product leads to

    P1[itex]\cdot[/itex]P1 = P12 = (P2+P3)[itex]\cdot[/itex](P2+P3).

    Leaving the rest to you. Essentially this is the laws of cosines.
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