Field and cuts

There is one place where the converter cannot give you everything, and it is worth being explicit about rather than discovering later. A CAD file describes a part. It cannot describe how you want that part simulated — how the magnetic field should be integrated through it, how long a step may be, which secondaries are worth producing. Those are simulation choices, and no CAD format has anywhere to record them.

Magnetic field

For the field there is a clean answer. Pass --in-field when the module sits inside the magnet, and the emitted macro will ask the live field for its integration method and maximum field strength at the moment the geometry is built — which is exactly what a hand-written O2 detector does from its own createMaterials(). Nothing is baked into the file:

geom.C · emitted

int   cad_ifield = 2;
float cad_fieldm = 10;
cadFieldTrackingParams(cad_ifield, cad_fieldm);   // queries the loaded field
med_Stainless_Steel->SetParam(1, cad_ifield);     // ifield, from the live field
med_Stainless_Steel->SetParam(2, cad_fieldm);     // fieldm, from the live field

The 2,10 you see there is only a seed, used if no field happens to be loaded, and --in-field 1,5.5 overrides it. To confirm that the query really happened, check fieldm rather than ifield: ifield = 2 is also the seed value and therefore proves nothing, whereas a fieldm the seed could not have produced — ALICE reports 15 — proves the live field answered.

Step control and physics cuts