LCDD XML Format

sensitive_detectors Element

The sensitive_detectors element contains definitions for all the unique readout configurations in the detector. sensitive_detector itself is an abstract type. Its basic, concrete subtypes are calorimeter, which can have a virtual segmentation of its volumes, and tracker, which writes out explicit step positions only.

The calorimeter-type sensitive detectors additionally have a volume segmentation tag, which is a concrete child class of segmentation. This specificies the virtual readout for assigned volumes. An example is gridXYZ, which reads out a uniform grid in up to 3 dimensions.

In addition to a name, each sensitive detector is assigned a hit collection. Also, an energy cut can be set to disregard low-energy hits, and verbosity can be assigned to output debugging information from specific sensitive detectors.

Following is an example sensitive_detectors element containing all the different combinations that are currently defined.

<sensitive_detectors>

  <calorimeter name="CalNP" (1)
                  hitsCollectionName="CalHitsA" 
                  ecut="0.25"
                  eunit="MeV"
                  verbose="0">

    <gridXYZ gridSizeX="5.0"
                gridSizeY="5.0"
                gridSizeZ="0.0"
                lunit="mm"/>

  </calorimeter>

  <calorimeter name="CalPrj" (2)
                  hitsCollectionName="CalHitsB"
                  ecut="0.25"
                  eunit="MeV"
                  verbose="0">

    <projectiveCylinder ntheta="1440" nphi="1440" />

  </calorimeter>

  <calorimeter name="CalPrjZ" (3)
                  hitsCollectionName="CalHitsC"
                  ecut="0.25"
                  eunit="MeV"
                  verbose="0">

    <projectiveZPlane ntheta="360" nphi="360" />

  </calorimeter>

  <calorimeter name="CalNPCyl" (4)
                  hitsCollectionName="CalNPCyl"
                  ecut="0.25
                  eunit="MeV"
                  verbose="0">

    <nonprojectiveCylinder gridSizeZ="1.0" 
                              gridSizePhi="1.0"
                              lunit="mm"/>

  </calorimeter>

  <tracker name="Tracker" (5)
              hitsCollectionName="TrackerHitsA" 
              ecut="0.25"
              eunit="MeV"
              verbose="0"/>

</sensitive_detectors>

The sensitive_detector element, either calorimeter or tracker, is referenced by name using an sdref in the extended volume element.

regions Element

Regions define several physics parameters used within the simulation.

The store_secondaries attribute defines whether secondary particles are written into the output file's particle tree.

The cut defines the Geant4 range cut for physics processes.

The threshhold attribute defines an energy cut for creating trajectories from secondary particles in this region.

<regions>
<region name="TrackingRegion"
           store_secondaries="true"
           cut="1.0"
           lunit="mm" 
           threshhold="0.25"
           eunit="MeV"/<

A region is assigned to a volume using the regionref tag.

fields Element

Global fields are defined using the fields element.

Currently, the only valid type of field is solenoid, which has an inner and outer field value and inner and outer radii.

The example below illustrates that the field values can be specified using expressions from the GDML define section.

<fields>
  <solenoid name="GlobalSolenoid"
               inner_field="solenoid_inner_field"
               outer_field="solenoid_outer_field"
               zmin="solenoid_zmin"
               zmax="solenoid_zmax"
               inner_radius="solenoid_rmin"
               outer_radius="solenoid_rmax"
               funit="tesla"
               lunit="mm"/>
  <global_field>
    <fieldref ref="GlobalSolenoid" />
  </global_field>
</fields>

Extended volume Element

The LCDD Schema formally extends the GDML Schema 2.0 using the standard XML Schema tag xs:extension. A few tags are added to GDML in order to link the LCDD objects, such as sensitive detectors, with their corresponding geometric volumes.

The only changes to GDML proper are made within the volume element, which corresponds to the Geant4 class G4LogicalVolume. This is a logical description of a detector element with a shape and material. Optionally, a G4Region can be assigned to the volume and a concrete instance of G4VSensitiveDetector can also be set for volume readout. Visualization attributes can be setup using G4VisAttributes.

<volume name="ecal_barrel">
  <materialref ref="Tungsten">
  <solidref ref="ecal_barrel_tube">

  <physvol>
    <volumeref ref="ecal_barrel_layer"/>
    <positionref ref="ecal_barrel_pos"/>
    <rotationref ref="ecal_barrel_rot"/>
    <physvolid value="ecal_id"/> (1)
  </physvol>

  <sdref ref="EcalSD"/> (2)
  <regionref ref="EcalRegion"/> (3)
</volume>

These three additional elements compromise all the alterations to the GDML format. This allows parsers using its standard schema to easily skip over these few, extra elements.