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Geometry Files

To specify a Mu2e geometry in the Mu2e Offline you put the following in the services table of your fcl file:

  GeometryService : { inputFile : <filename> }
where <filename> is the name of a geometry file. A typical services table will contain configuration for other services. To choose the currently recommended geometry, use the file:
where the path is relative to a base release of Mu2e Offline. If you look at this file, you will see that it contains only one line: it includes one of the named geometries. As of July 2016, there five supported named geometries:
The current default is the first in this list.

If you wish to override the choice of the geometry file, the recommended procedure is to add the following at the bottom of your fcl file:

services.GeometryService.inputFile : <filename>
Some comments on each of these follows:


Relative to geom_common_cd3_s4p2.txt there is one change: the tracker has all 20 stations (not 18 - see the comment in the description of geom_common_cd3_s4p2.txt). This file is used to generate, but not to reconstruct, events in stage 4 pass 2. The strategy is to run g4 on a 20 station tracker. When we make hits we skip straws from the missing stations. In this way we can study trackers with 18, 19 or 20 stations without having to rerun G4.


This file should be used to analyze files produced by the second pass of stage 4 onward. It is the current default (July 2016). Relative to geom_common_cd3_s3p2.txt this has the following changes: In this geometry the tracker design has slots for 20 stations but only 18 stations are present. In the CD3 design we only have money to build 18 stations. Should the finanacial situation improve, we will build one or two more stations and install them in the available slots.


This file was used for the second pass of stage 3 and for the first pass of stage 4. Relative to geom_common_cd3_p1.txt it has the following changes:


This is the geometry file used to run passes 1 and 2 of the beam simulations in the CD3 simulation campaign. It was also used for the first pass of stage 3. It has TDR era descriptions of the tracker and calorimeter but in these stages those detectors are hidden.


With this geometry file, one can use modern code to analyze the tracker information from TDR era event-data files; be aware when you make hits from the StepPointMCs you will use modern code for hit making - you will not get TDR era hits. You can also do some limited analysis with the calorimeter information from TDR era files; when you make hits you may use code that loads CsI properties by default - you may also need to modify conditions information to get properties of BaF2. Check this out before using this code to look at calorimeter information. If you need to look at other information from TDR era files, you should use code from that era.

Some Ancient History about Geometry files

Before March 2015, the standard Mu2e geometry file was named:

and the module that interfaced to Geant4 was called:
For historical reasons most of the run-time configurable parameters of G4_module were put into the geometry file. For a long time we wanted to move these parameters from the geometry file and put them into the fcl parameter set of G4_module.

In March 2105 a new module was created,

At this point G4_module was frozen and future improvments were made in Mu2eG4_module. In Mu2eG4_module, the non-geometry parameters were moved out of the geometry file and into the fcl parameter set used to configure the module.

For a while both modules co-existed. To support this, the geometry file geom_01.txt was split into two pieces so that it was reduced to two lines:

#include "Mu2eG4/geom/geom_common.txt"
#include "Mu2eG4/geom/g4_userOptions.txt"
The first include file contains the geometry description and the second contains the geant4 non-geometry options.

During this period the two legal configurations were:

// Using G4_module:
services.GeometryService.inputFile : "Mu2eG4/test/geom_01.txt"
physics.producers.g4run            : @local::g4run
// Using Mu2eG4_module:
services.GeometryService.inputFile : "Mu2eG4/geom/geom_common.txt"
physics.producers.g4run            : @local::mu2eg4runDefaultSingleStage
There are two things to note here: There are two ways to misconfigure jobs:
services.GeometryService.inputFile : "Mu2eG4/test/geom_01.txt"
physics.producers.g4run            : @local::mu2eg4runDefaultSingleStage
services.GeometryService.inputFile : "Mu2eG4/geom/geom_common.txt"
physics.producers.g4run            : @local::g4run
In both cases the module will detector that it was given the wrong geometry file, issue an error message and stop the job.

When G4_module was retired, Mu2eG4/test/geom_01.txt was modifed so that it no longer included Mu2eG4/geom/g4_userOptions.txt; this made it identical to Mu2eG4/geom/geom_common.txt. And the definition of g4run was changed to be a copy of mu2eg4runDefaultSingleStage. With these changes most legacy configurations were transformed to the new system without having to edit the legacy configurations.

At this time was changed to give an error message and stop the job. It will be deleted in the near future.

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This file last modified Wednesday, 27-Jul-2016 20:07:52 CDT
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