The particles available to SMASH are defined in particles.txt, which is located in '$SMASH_SRC_DIRECTORY/input'. If you want to modify and use this file to set up SMASH, execute

./smash -p $SMASH_SRC_DIRECTORY/input/particles.txt

in the '$SMASH_SRC_DIRECTORY/build' directory.
The particles are given as a table with the particles properties in different columns. Note, that these columns may be separated by an arbitrary number of spaces:

The name has to be a unique UTF-8 string. Conventionally, unicode names are used in SMASH to make the file more readable and generate prettier output. It is possible to only specify the isospin multiplet and SMASH will fill in the properties of the components of the multiplet assuming isospin symmetry. The names generated this way will have the charges appended to the multiplet name using the unicode characters ⁻, ⁰ and ⁺. This is appropriate for almost all particles. Anti particles do not have to be specified explicitely.

The pole mass and the on-shell width of the particle or multiplet have to be specified as floating point numbers in GeV.

The parity has to be either + or -.

The PDG codes are following the numbering scheme specified by the PDG, which depends on the quantum numbers of the particles. For SMASH, it is important that the quark content in the PDG code is correctly specified. Other than that, deviations from the numbering scheme have no effect in SMASH. If the name represents a multiplet, there has to be a PDG code for all multiplet members, except for anti particles.

For example, to define all three pions (π⁻, π⁰, π⁺), it is sufficient to specify the π multiplet using the following line in particles.txt, where the 4th column contains the PDG number of the neutral and the 5th PDG number of the charged state:

π 0.138 7.7e-9 111 211

It is also possible to only specify a specific member of the multiplet. In this case, the charge has to be given as a suffix in the name using the UTF-8 unicode characters ⁻, ⁰ and ⁺. For example, the properties of the electron can be specified like this:

e⁻ 0.000511 0 11

Comments can be added to particles.txt using the # character. Everything after # until the end of the line is ignored.

Note that some reactions in SMASH are parametrized and require specific particles in the final state. When such a reaction happens and the required particle is not defined, SMASH will crash.

If you specify an incorrect value, SMASH will print an error similar to the following:

Failed to convert the input string to the expected data types.

When running a box simulation in which detailed balance is expected to be conserved, the particles file will need to be modified. See Box for further information.