\page ExampleRE07 Example RE07

This example is based on extended/electromagnetic/TestEm3 and
demonstrates how to register specialized tracking managers for
a particle or a set of particles.

## Geometry definition

The geometry of a simplified sampling calorimeter is used as
in [TestEm3](../../html_TestEm3/html/ExampleTestEm3.html), please refer to its
documentation for more details.
The same UI commands exist for modifying the geometry (number
of layers and absorbers, material and its thickness), without
the /testem/ prefix.

In addition to the definition of the volumes, this example adds
two regions, "Front" and "Back", which contain the front and
rear half of the calorimeter.

## Physics lists

By default, the example uses G4EmStandardPhysics and registers
processes to the G4ProcessManager. This can be changed with the
`/setMode` UI command. Possible values are:

- processes:   use G4EmStandardPhysics, the default
- tracking:    use the same physics as G4EmStandardPhysics, but
               implemented as a specialized tracking manager for
               electrons, positrons, and gammas; see the file
               EmStandardPhysicsTrackingManager.cc for details.
- specialized: use a specialized tracking manager for gammas; for
               the purpose of demonstration,
               - it uses G4EmStandardPhysics as the basis,
               - defers processing of gammas with a kinetic energy
                 of more than 100 MeV,
               - implement a specialized stepping loop for the
                 "Back" region of the detector.
               See the file SpecializedTrackingManager.cc for more
               details on the exact implementation.

## How to start?

This example comes with one macro file for each of the described
modes (processes.mac, specialized.mac, tracking.mac)
that can be passed as a parameter to the executable:

```
% ./exampleRE07 processes.mac
% ./exampleRE07 specialized.mac
% ./exampleRE07 tracking.mac
```