The Collider modus can be customized using the options here below. To further configure the projectile, target and the impact parameter, see

Attention: The incident energy can be specified in different ways and one (and only one) of these must be used. 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 or E_Kin or P_Lab for both Projectile and Target.

Ways to specify incident energies → Only one can be given!

E_Kin — double, required

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 as described in Projectile and target. This key can be omitted if the incident energy is specified in a different way.

E_Tot — double, required

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 as described in Projectile and target. This key can be omitted if the incident energy is specified in a different way.

P_Lab — double, required

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 as described in Projectile and target. This key can be omitted if the incident energy is specified in a different way.

Sqrtsnn — double, required

Defines the energy of the collision in GeV as center-of-mass energy in the collision of two hadrons, one for each nucleus, having the average mass of all the hadrons composing the given nucleus. This key can be omitted if the incident energy is specified in a different way.

Calculation_Frame — string, optional, default = "center of velocity"

The frame in which the collision is calculated. Possible values are

"center of velocity"
"center of mass"
"fixed 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.

Collisions_Within_Nucleus — bool, 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.

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.

Initial_Distance — double, optional, default = 2.0

The initial distance of the two nuclei in fm: \(z_{\rm min}^{\rm target} - z_{\rm max}^{\rm projectile}\).

Note that this distance is applied before the Lorentz boost to the chosen calculation frame, and thus the actual distance may be different.

Example of heavy-ion collision configuration

The following example configures a Cu63-Cu63 collision at \(\sqrt{s_{NN}}=3.0\,\mathrm{GeV}\) 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. Refer to Projectile and target for information about the Particles and Target sections.

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 from the codebase build folder without further specifying the configuration, particles and decay modes files, a collider simulation is set up according to the default config.yaml, particles.txt and decaymodes.txt files located in the input directory at the top-level of the codebase. However, changing the input directory content will not affect the default SMASH run, unless a clean build folder is created over again. This is because the triplet of input files are transformed into another triplet of files into the build directory when cmake is run. Hence prefer to use smash command line options in case you want to refer to possibly modified configuration, particles and decay modes files.
To run SMASH in the (default) collider setup, execute

   ./smash

from the codebase build folder.