Projectile and Target

Projectile:
Section for projectile nucleus. The projectile will start at \(z < 0\) and fly in positive \(z\)-direction, at \(x \ge 0\).

Target:
Section for target nucleus. The target will start at \(z > 0\) and fly in negative \(z\)-direction, at \(x \le 0\).

Projectile: and Target:

• Particles (int:int, int:int, required):
  A map in which the keys are PDG codes and the values are number of particles with that PDG code that should be in the current nucleus. E.g. Particles: {2212: 82, 2112: 126} for a lead-208 nucleus (82 protons and 126 neutrons = 208 nucleons), and Particles: {2212: 1, 2112: 1, 3122: 1} for Hyper-Triton (one proton, one neutron and one Lambda).

• Diffusiveness (double, optional, default = (0.545 for A <= 16; 0.54 for A > 16)):
  Diffusiveness of the Woods Saxon distribution for the nucleus in fm.

• Radius (double, optional, default = proton_rad * A^(1/3)):
  Radius of nucleus in fm. The default radius is calculated as the proton radius times the third root of the number of nucleons.

• Saturation_Density (double, optional, default = 0.168):
  Saturation density of the nucleus in 1/fm^3.

• Deformed:
  
  • Automatic (bool, required if Deformed exists, no default):
    true - Set parameters of spherical deformation based on mass number of the nucleus.
    flase - Manually set parameters of spherical deformation. This requires the additional specification of Beta_2, Beta_4, Theta and Phi, which follow Moller:1993ed.
    
  • Beta_2 (double, optional):
    The deformation coefficient for the spherical harmonic Y_2_0 in the beta decomposition of the nuclear radius in the deformed woods-saxon distribution.
    
  • Beta_4 (double, optional):
    The deformation coefficient for the spherical harmonic Y_4_0.
    
  • Theta (double, optional):
    The polar angle by which to rotate the nucleus.
    
  • Phi (double, optional):
    The azimuthal angle by which to rotate the nucleus.
  
  

Custom:

• File_Directory (path, required if Custom exists):
  The directory where the external list with the nucleon configurations is located. Make sure to use an absolute path.
  
• File_Name (string, required if Custom exists):
  The file name of the external list with the nucleon configurations.

Example: Configuring a deformed nucleus

To configure a fixed target heavy-ion collision with deformed nuclei, whose spherical deformation is explicitly declared, it can be done according to the following example. For explanatory (and not physics) reasons, the projectile's Woods Saxon distribution is initialized automatically and it's spherical deformation manually, while the target nucleus is configured just the opposite.

Modi:
    Collider:
        Projectile:
            Particles:    {2212: 29, 2112: 34}
            Deformed:
                # Manually set deformation parameters
                Automatic: False
                Beta_2: 0.1
                Beta_4: 0.3
                Theta: 0.8
                Phi: 0.02
        Target:
            Particles:    {2212: 29, 2112: 34}
            # manually set woods saxon parameters
            Saturation_Density: 0.1968
            Diffusiveness: 0.8
            Radius: 2.0
            Deformed:
                # Automatically set deformation parameters
                Automatic: True
        E_kin: 1.2
        Calculation_Frame: "fixed target"

Example: Configuring custom nuclei from external file

The following example illustrates how to configure a center-of-mass heavy-ion collision with nuclei generated from an external file. The nucleon positions are not sampled by smash but read in from an external file. The given path and name of the external file are made up and should be defined by the user according to the used file.

Modi:
    Collider:
        Projectile:
            Particles:    {2212: 79, 2112: 118}
            Custom:
                File_Directory: "/home/username/custom_lists"
                File_Name: "Au197_custom.txt"
        Target:
            Particles:    {2212: 79, 2112: 118}
            Custom:
                File_Directory: "/home/username/custom_lists"
                File_Name: "Au197_custom.txt"
        Sqrtsnn: 7.7

The following example shows how an input file should be formatted:

 0.20100624 0.11402423 -2.40964466 0 0
 1.69072087 -3.21471918 1.06050693 0 1
-1.95791109 -3.51483782 2.47294656 1 1
 0.43554894 4.35250733 0.13331011 1 0

The input file contains 5 columns (x, y, z, s, c). The first three columns specify the spatial cordinates in fm. The fourth column denotes the spin projection. The fifth contains the charge with 1 and 0 for protons and neutrons respectively. In the example given the first line defines a neutron and the second one a proton. Please make sure that your file contains as many particles as you specified in the configuration. For the example configuration your file needs to contain 79 protons and 118 neutrons in the first 197 lines. And the same number in the following 197 lines. For every event you need to create 2 nuclei. It is crucial that your file contains enough nucleons for the number of events you want to simulate.

Note

SMASH is shipped with an example configuration file to set up a collision with externally generated nucleon positions. This requires a particle list to be read in. Both, the configuration file and the particle list, are located in /input/custom_nucleus. To run SMASH with the provided example configuration and particle list, execute

   ./smash -i INPUT_DIR/custom_nucleus/config.yaml

Where 'INPUT_DIR' needs to be replaced by the path to the input directory ('../input', if the build directory is located in the smash folder).