Dilepton production can be enabled in the corresponding Dilepton section of the configuration file. Currently, there are the following options:

Decays (bool, optional, default = false):
Whether or not to enable dilepton production from hadron decays. This includes direct decays as well as Dalitz decays. Dilepton decays additionally have to be uncommented in the used decaymodes.txt (see also note below).

Remember to also activate the dilepton output in the output section.

Dilepton production in SMASH

The treatment of Dilepton Decays is special:

Dileptons are treated via the time integration method, also called 'shining', as e.g. described in Schmidt:2008hm [9], chapter 2D. This means that, because dilepton decays are so rare, possible decays are written in the output at every hadron propagation without ever performing them. The are weighted with a "shining weight" to compensate for the over-production.
The shining weight can be found in the weight element of the output.
The shining method is implemented in the DecayActionsFinderDilepton, which is automatically enabled together with the dilepton output.

Note: If you want dilepton decays, you have to modify the decaymodes.txt of your choice, which you then specify as the input with the -d command line option. Without this decay modes modification the dilepton output will be empty.
Dilepton decays are commented out by default. You therefore need to uncomment them. Note, that for dilepton decays, new decay channels can not simply be added to the decaymodes.txt file. You also have to modify the decay width formulas TwoBodyDecayDilepton::width and ThreeBodyDecayDilepton::diff_width in '$SMASH_SRC_DIRECTORY/src/decaytype.cc'.

Examples: Configuring Dileptons
The following example configures the dilepton production for dileptons originating from resonance decays. In addition, the extended OSCAR2013 dilepton output is enabled.

Output:
  Dileptons:
      Format:             ["Oscar2013"]
      Extended: True
Collision_Term:
  Dileptons:
      Decays:    True