Collider

Possible Incident Energies, only one can be given:

• Sqrtsnn (double, optional, no default):
  Defines the energy of the collision as center-of-mass energy in the collision of one participant each from both nuclei (using the average participant mass in the given nucleus).

• E_Kin (double, optional, no default):
  Defines the energy of the collision by the kinetic energy per nucleon of the projectile nucleus (in AGeV). This assumes the target nucleus is at rest. Note, this can also be given per-beam.

• E_Tot (double, optional, no default):
  Defines the energy of the collision by the total energy per nucleon of the projectile nucleus (in AGeV). This assumes the target nucleus is at rest. Note, this can also be given per-beam.

• P_Lab (double, optional, no default):
  Defines the energy of the collision by the initial momentum per nucleon of the projectile nucleus (in AGeV). This assumes the target nucleus is at rest. This must be positive. Note, this can also be given per-beam.

Alternatively, one can specify the individual beam energies or momenta in the Projectile and Target sections (see Projectile and Target for details). In this case, one must give either E_Tot for both Projectile and Target, E_Kin for both Projectile and Target, or P_Lab for both Projectile and Target.

Note

Using E_Tot, E_kin or P_Lab to quantify the collision energy is not sufficient to configure a collision in a fixed target frame. You need to additionally change the Calculation_Frame. Any format of incident energy can however be combined with any calculation frame, the provided incident energy is then intrinsically translated to the quantity needed for the computation.

Calculation_Frame (string, optional, default = "center of velocity"):
The frame in which the collision is calculated.

• "center of velocity"
• "center of mass"
• "fixed target"

Fermi_Motion (string, optional, default = "off"):

• "on" - Switch Fermi motion on, it is recommended to also activate potentials
• "off" - Switch Fermi motion off
• "frozen" - Use "frozen" if you want to use Fermi motion without potentials

Collisions_Within_Nucleus (string, optional, default = false)
Determine whether to allow the first collisions within the same nucleus.

• true - First collisions within the same nucleus allowed
• false - First collisions within the same nucleus forbidden

Initial_Distance (double, optional, default = 2.0):
The initial distance of the two nuclei in fm. That means \(z_{\rm min}^{\rm target} - z_{\rm max}^{\rm projectile}\).
Note that this distance is applied before the Lorentz boost to the chosen calculation frame, and thus the actual distance may be different.

To further configure the projectile, target and the impact parameter, see

• Projectile and Target
• Impact Parameter

Examples: Configuring Heavy-ion Collisions
The following example configures a Cu63-Cu63 collision at \(\sqrt{s_{NN}}=3.0\) GeV with zero impact parameter and Fermi motion taken into consideration. The calculation frame is the default, center of velocity, and the nuclei are not deformed.

Modi:
    Collider:
        Projectile:
            Particles:    {2212: 29, 2112 :34}
        Target:
            Particles:    {2212: 29, 2112 :34}
        Sqrtsnn: 3.0

To further use Fermi motion and allow the first collisions within the projectile or target nucleus, the corresponding options need to be activated by means of:

        Fermi_Motion: "on"
        Collisions_Within_Nucleus: True

Additionally, the impact parameter may be specified manually. See Impact Parameter for an example.

Note

By default, executing SMASH without further specifying the configuration, particles or decaymodes, a collider simulation is set up according to the default 'config.yaml', 'particles.txt' and 'decaymodes.txt' files located in /input. Note though that these files were previously copied to the build directory, so changng the ones in the /input directory will not affect the default SMASH run. To run SMASH in the (default) collider setup, execute

   ./smash