2.12 Detector Simulation

Simulated events are of great importance in checking and/or correcting for non-trivial or unforeseen detector or physics effects, as well as comparing detector performance with expectations. With the possible exception of the effect being studied, simulated events should be as close as possible to real data events. Hence the primary goal of the simulation programme is to model closely the physical interactions involved, the detector performance, and the event reconstruction.

The DELPHI simulation program, DELSIM [77], is composed of three main components: generators, tracking, and detector response.

1. The primary physics processes can be modelled using a variety of generators. For Standard Model hadronic production, the JETSET [78] generator is most commonly used. This simulates $\ensuremathbox{\mathrm{e^+ e^-}}\ensuremathbox{\rightarrow}\ensuremathbox{\mathrm{Z^0}}\ensuremathbox{\rightarrow}\ensuremathbox{\mathrm{q\bar{q}}}$ and hadronization, producing a set of four-vectors for the next stage. JETSET model parameters are tuned using LEP data.

2. In DELSIM, particles are tracked through the detector, accounting for weak decays, curvature in the magnetic field, ionization energy loss, multiple scattering, the photoelectric effect, delta ray emission, bremsstrahlung, positron annihilation, pair production, Compton scattering, and nuclear interactions.^2.11

3. Subsequently, the response of each part of the detector is simulated, producing a set of simulated electronic signals.

Since the output of DELSIM closely models the real raw data produced by the DAS, DELANA can be used directly, thus well-modelling the real data reconstruction. Like DELANA, DELSIM uses CARGO to store the detector geometry, material descriptions, and sensing device parameters (e.g. noise and efficiency). In principle, this allows simulated events to be produced for the current or any previous detector configuration.