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## /ThreeMeson [ Modules ]

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NAME

module ThreeMeson

PURPOSE

This module implements the back reaction 3 -> 1 of mesonic decay channels

INPUTS

(none)

## ThreeMeson/DoThreeMeson [ Subroutines ]

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NAME

subroutine DoThreeMeson(time)

PURPOSE

process all the finding of possibilities for 3->1 resonance decay back reactions. Actually also do the collision.

## ThreeMeson/calcPhi3 [ Functions ]

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NAME

real function calcPhi3(srts,m3)

PURPOSE

Calculate the 3-particle phase space. Particle 1 and 2 are pions.

INPUTS

OUTPUT

return value in GeV^2

NOTES

there is threeBodyPhaseSpace/Integrate_3bodyPS, which does the same, but just by simply adding 100 values. This here is closer to mesonWidthVacuum/threepi

We calculate the integral of

  \dd\Phi_n(P;p_1,\dots,p_n) = (2\pi)^4\delta^{(4)}(P-p_1-\dots-p_n)
\prod_i{\frac{\dd^3p_i}{(2\pi)^3\,2E_i}}
=
(2\pi)^4\delta^{(4)}(P-p_1-\dots-p_n)
\prod_i{\frac{\dd^4p_i}{(2\pi)^4}}
(2\pi)\delta(p_i^2-m_i^2)\Theta(p_i^0)


Here the definition of the n-body phase space is slightly (by a factor $(2\pi)^4$) modified compared to the PDG\cite{Beringer:1900zz} version.

## ThreeMeson/ThreeMeson_INIT [ Subroutines ]

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NAME

subroutine ThreeMeson_INIT()

PURPOSE

This routine initializes the 3-meson routines. It sets up internal arrays.

## ThreeMeson/ThreeMeson_DoColl [ Subroutines ]

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NAME

subroutine ThreeMeson_DoColl(Part1,Part2,Part3, ID, time)

PURPOSE

This routine does the actual collision. It replaces Part1 with the mother particle and erases Part2 and Part3