Uniform distribution in Energy and Theta LUND files

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4.1 Uniform Distribution in Energy and Theta LUND files

File:LUND Spread.C

Due to the fact that GEMC simulations will utilize particle momentum in the lab frame, the LUND files must contain lab frame information. In addition, all the data given is for particles that have not yet had the chance to interact with the target material. In the lab frame there are 2 degrees of freedom, i.e. [math]P_{\theta}[/math] and [math]P_{\phi}[/math] . The number of degrees of freedom can be reduced to 1 degrees of freedom in the center of mass frame of reference since the Moller differential cross section does not rely on [math]\phi[/math]. Since the Moller differential cross-section only relies on [math]\theta[/math] in this frame it implies for a given angle [math]\theta[/math] we should find the same results for any given angle [math]\phi[/math]. To ensure that all the particles simulated in GEMC are Moller particles, this is made easier by first creating Moller particles in the center of mass frame. The LUND file is created by creating an isotropic distribution of particles within the Moller Center of Mass frame of reference. These particles are uniformly distributed through the angle theta with respect to the beam line in the range 90-180 in the Center of Mass frame. This is initially done at a set angle phi (0 degrees) with respect to the perpendicular components with respect to the beam line.

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