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. For copper, zirconium, ruthenium, gold, lead and uranium, a more specific default value is used.

Radius (double, optional, default = 1.2 * A^(1/3) for A <= 16, else 1.12 * A^(1/3) - 0.86 * A^(-1/3)):
Radius of nucleus in fm. For copper, zirconium, ruthenium, gold, lead and uranium, a more specific default value is used.

Saturation_Density (double, optional, default = 0.168):
Saturation density of the nucleus in 1/fm^3. For copper, zirconium, ruthenium, gold, lead and uranium, a more specific default value is used.

Possible incident energies when given per beam:
- E_Tot (double, optional, no default) Set the total energy (in GeV) per particle of the beam. This key, if used, must be present for both Projectile and Target.
- E_Kin (double, optional, no default) Set the kinetic energy (in GeV) per particle of the beam. This key, if used, must be present for both Projectile and Target.
- P_Lab (double, optional, no default) Set the momentum (in GeV/c) per particle of the beam. This key, if used, must be present for both Projectile and Target, and must be positive for both beams.

Note: If the beam specific kinetic energy or momentum is set using either of these keys, then it must be specified in the same way (not necessarily same value) for both beams. This is for example useful to simulate for p-Pb collisions at the LHC, where the centre-of-mass system does not correspond to the laboratory system (see example below).

Example: p-Pb collisions at the LHC
Note that SMASH performs it's calculation in the centre-of-velocity and the particles are returned in the centre-of-mass frame. The particles therefore need to be boosted by the rapidity of the centre-of-mass (-0.465 for p-Pb at 5.02TeV).

Modi:
  Collider:
    Calculation_Frame: center of velocity
    Impact:
      Random_Reaction_Plane: True
      Range: [0, 8.5]
    Projectile:
      E_Tot: 1580
      Particles:
        2212: 82
        2112: 126
    Target:
      E_Tot: 4000
      Particles:
        2212: 1
        2112: 0

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 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:

20100624 0.11402423 -2.40964466 0 0
69072087 -3.21471918 1.06050693 0 1
-1.95791109 -3.51483782 2.47294656 1 1
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. The read in nuclei are randomly rotated and recentered. Therefore you can run smash even if your file does not contain enough nuclei for the number of events you want to simulate as the missing nuclei are generated by rotation of the given configurations.

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).

Deformed:
- Automatic (bool, required if Deformed exists, no default):
  - true - Set parameters of spherical deformation based on mass number of the nucleus. Currently the following deformed nuclei are implemented: Cu, Zr, Ru, Au, Pb, U.
  - false - Manually set parameters of spherical deformation. This requires the additional specification of Beta_2, Beta_4, Theta and Phi, which follow Moller:1993ed [34] and Schenke:2019ruo [42].
    - 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.
    - Orientation
      Determines the orientation of the nucleus by rotations which are performed about the axes of a coordinate system that is fixed with respect to the nucleus and whose axes are parallel to those of the computational frame before the first rotation. Note that the nucleus is first rotated by phi and then by theta.
      - Phi (double, optional, default = 0):
        The angle by which to rotate the nucleus about the z-axis.
      - Theta (double, optional, default = pi/2):
        The angle by which to rotate the nucleus about the rotated x-axis.
      - Random_Rotation (bool, optional, default = false):
        Determines whether the created nucleus object should be randomly rotated in space.

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 its 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
                Orientation:
                    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
                Orientation:
                    # Randomly rotate nucleus
                    Random_Rotation: True
        E_kin: 1.2
        Calculation_Frame: "fixed target"