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Version: SMASH-3.1
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Version: SMASH-3.1
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Within the Collider section, two sections can be used for further customizations:
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 \(x \le 0\).All keys described here below can be specified in the Projectile and/or in the Target section. Examples are given after the keys description.
Diffusiveness — double, optional, default = \(d(A)\)
Diffusiveness of the Woods-Saxon distribution for the nucleus in fm. In general, the default value is
\[ d(A)=\begin{cases} 0.545 & A \le 16\\ 0.54 & A > 16 \end{cases}\;. \]
For copper, zirconium, ruthenium, xenon, gold, lead and uranium, a more specific default value is used (see nucleus.cc).
Particles — map<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. For example:
{2212: 82, 2112: 126} → a lead-208 nucleus (82 protons and 126 neutrons = 208 nucleons){2212: 1, 2112: 1, 3122: 1} → for Hyper-Triton (one proton, one neutron and one \(\Lambda\)).Radius — double, optional, default = \(r(A)\)
Radius of nucleus in fm. In general, the default value is
\[ r(A)=\begin{cases} 1.2 \, A^{1/3} & A \le 16\\ 1.12 \, A^{1/3} - 0.86 \, A^{-1/3} & A > 16 \end{cases}\;. \]
For copper, zirconium, ruthenium, xenon, gold, lead, and uranium, a more specific default value is used (see nucleus.cc).
Saturation_Density — double, optional, default = \(\int\rho(r)\:\mathrm{d}^3r=N_{nucleons}\)
Saturation density of the nucleus in 1/fm³. If not any value is specified, the saturation density is calculated such that the integral over the Woods-Saxon distribution returns the number of nucleons in the nucleus.
Set the kinetic energy in GeV per particle of the beam. This key, if used, must be present in both Projectile and Target section. This key can be omitted if the incident energy is specified in a different way.
Set the totat energy in GeV per particle of the beam. This key, if used, must be present in both Projectile and Target section. This key can be omitted if the incident energy is specified in a different way.
Set the momentum in GeV per particle of the beam. This key, if used, must be present in both Projectile and Target section. This key can be omitted if the incident energy is specified in a different way.
It is possible to further customize the projectile and/or target using the Custom section, which should then contain few required keys, if given.
File_Directory — string, required
The directory where the external list with the nucleon configurations is located. Make sure to use an absolute path!
The file name of the external list with the nucleon configurations.
It is possible to deform the projectile and/or target nuclei using the Deformed section, which should then contain some configuration, if given.
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, and Xe (see deformednucleus.cc). If set to true the other parameters should not be provided.false → Manually set parameters of spherical deformation. This requires the additional specification of at least one among Beta_2, Beta_3, Beta_4, which follow Moller:1993ed [7] and Schenke:2019ruo [10]. These parameters enter the radius in the Wood-Saxon profile as follows, \[ R(\theta,\phi) = R_0 \cdot \biggl\{ 1+ \beta_2\,\Bigl[\cos\gamma\, Y_2^0(\theta,\phi) + \sqrt{2}\,\sin\gamma\,\Re\bigl(Y_2^2(\theta,\phi)\bigr)\Bigr]+ \beta_3^{\phantom{0}}\,Y_3^0(\theta,\phi)+ \beta_4^{\phantom{0}}\,Y_4^0(\theta,\phi) \biggr\} \]
and are set to 0 if not specified.Beta_2 — double, optional, default = 0.0
The deformation coefficient \(\beta_2\) for the spherical harmonic \(Y_2^0\) in \(R(\theta,\phi)\) above.
Beta_3 — double, optional, default = 0.0
The deformation coefficient \(\beta_3\) for the spherical harmonic \(Y_3^0\) in \(R(\theta,\phi)\) above.
Beta_4 — double, optional, default = 0.0
The deformation coefficient \(\beta_4\) for the spherical harmonic \(Y_4^0\) in \(R(\theta,\phi)\) above.
Gamma — double, optional, default = 0.0
The parameter describes triaxiality \(\gamma\) of the nucleus in \(R(\theta,\phi)\) above.
In the Orientation section it is possible to specify 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 = 0.0
The angle by which to rotate the nucleus about the z-axis.
Psi — double, optional, default = 0.0
The angle by which to rotate the nucleus about the rotated y-axis.
Random_Rotation — bool, optional, default = false
Whether the created nucleus object should be randomly rotated in space.
Theta — double, optional, default = π/2
The angle by which to rotate the nucleus about the rotated x-axis.
Note that SMASH performs its 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
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 Au197_custom.txt file should be formatted as follows:
It 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 considered here, the 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.
./smash -i INPUT_DIR/custom_nucleus/config.yamlwhere
INPUT_DIR needs to be replaced by the path to the input directory at the top-level of SMASH codebase.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_3: 0.2
Beta_4: 0.3
Orientation:
Theta: 0.8
Phi: 0.02
Psi: 0.13
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"