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3 Body Decay Kinematics (Width Calc): Examples?

  1. May 24, 2012 #1


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    Does anyone know of any worked out examples for the calculation of the width of a 1->3 decay process, where ALL THREE masses are included?

    I can find a LOT of examples where they let the masses go to zero, (like leptonic/semi leptonic decays, decays to pions, etc). This makes the integrals over the dalitz phase space easy.

    Basically I would love an example, even if its a textbook of the full calculation of a width of a particle P decaying to particles p1, p2 ,p3, where the masses are taken into account with NO approximation.

    Even something simple, like if the amplitude squared was "1". I can't find an easy way to do the integrals, and I think for this case theyll be elliptic functions, and in my case actually dilogarithms, but I'm not sure. Mathematica doesnt seem to be much help either. Most of the integrals I try just seem to be spit back out at me, even with the correct $assumptions set.

    d \Gamma = \frac{1}{(2 \pi)^3} \frac{M}{32} |A|^2 ds dt

    where [itex] M^2 s = (p_1 + p_2)^2[/itex] and [itex] M^2 t = (p_2 +p_3)^2[/itex].

    (I chose to use unitless variables.) I get my kinematic boundaries from : http://www.slac.stanford.edu/xorg/BFLB/draft_sections/pbf-DalitzAnalyses.pdf [Broken]

    Which I believe is correct.

    So basically the first integration over t for unity would be trivial, and you plug in the following limits:
    t_{min}^{max} = \frac{1}{2 s} (-s^2+(\rho_1-\rho_2) (\rho_1+\rho_2) \left(-1+\rho_3^2\right)+s)\biggl[1+\rho_1^2+\rho_2^2+\rho_3^2\pm\sqrt{\frac{\left(s-\rho_1^2\right)^2-2 \left(s+\rho_1^2\right) \rho_2^2+\rho_2^4}{s}} \sqrt{\frac{(-1+s)^2-2 (1+s) \rho_3^2+\rho_3^4}{s}}\biggr]

    Then you're integrating over this which becomes quite complicated.

    Are there tricks that I should know, or relevant formalisms used for these calculations? Any help would be appreciated.
    Thank you.
    Last edited by a moderator: May 6, 2017
  2. jcsd
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