The available process types are summarized in the following table.
| Process number | Description |
0 | No previous process yet, particle was created at initialization |
1 | Elastic scattering |
2 | Resonance formation (2 → 1) |
3 | Inelastic binary scattering (2 → 2) |
4 | Inelastic multi-particle scattering (2 → 3) |
5 | Resonance decay |
6 | Box wall crossing (due to periodic boundary conditions) |
7 | Forced thermalization, many particles are replaced by a thermalized ensemble |
8 | Fluidization, particles that obey the fluidization condition given in the configuration file are removed from the evolution and printed to a separate output, to serve as initial conditions for hybrid models. |
21 | Fluidization as above, but particles are not removed from the evolution. They are instead tagged as core. |
9 | Bremsstrahlung process: a + b → a + b + photon |
16 | Bremsstrahlung process: a + b → a + b + dilepton |
10 | Inelastic multi-particle meson scattering (3 → 1) |
11 | Inelastic multi-particle scattering (3 → 2) |
12 | Inelastic multi-particle scattering (5 → 2) |
13 | Inelastic multi-particle scattering (2 → 5) |
14 | Inelastic multi-particle scattering (4 → 2) |
15 | Inelastic multi-particle scattering (2 → 4) |
41 | Soft string excitation, single diffractive AB → AX. Both quark and anti-/di-quark taken from B. |
42 | Soft string excitation, single diffractive AB → XB. Both quark and anti-/di-quark taken from A. It makes sense to distinguish it from AB → AX, because A and B can be particles of different types, for example, a pion and a proton. It matters then whether the pion or the proton creates the string. |
43 | Soft string excitation, double diffractive. Two strings are formed, one from A and one from B. |
44 | Soft string N-Nbar annihilation, a special case of baryon-antibaryon annihilation. One pair qqbar annihilates immediately and then two strings are formed. |
45 | Soft string excitation, non-diffractive. Two strings are formed, both have ends in A and B. |
46 | Hard string excitation, non-diffractive. A hard 2 → 2 QCD process is generated by PYTHIA. Here quarks or gluons scatter at parton level before the strings are formed. |
47 | Hard string excitation, single diffractive AB → AX. Generated by PYTHIA with a hard diffractive process. |
48 | Hard string excitation, single diffractive AB → XB. Generated by PYTHIA with a hard diffractive process. |
49 | Hard string excitation, double diffractive. Generated by PYTHIA with a hard diffractive process. |
50 | Failed string process. A string process can fail due to lack of energy. This tag is added to avoid mislabeling the event. |
90 | Add or remove particle(s) process, which ignores conservation laws. It can be thought of as a 0 → 1 or a 1 → 0 process. |
