21-Sep-1999 GEANT4 implementation test of barrel EM calorimeter

We are testing a set of OO tools developed in BNL. These tools have been provided by the NOVA framework for distributed computing.

Now we can access the detector description parameters held in the GEANT3 parameters database from GEANT4 code. We believe it will be useful for the G3 to G4 transition in ATLAS.

Preliminary LAr barrel code

Version 0.0.1 of the code of test GEANT4 implementation of the barrel electromagnetic (EM) calorimeter has been released by M. Leltchouk on September 17, 1999.

The goal of this version is to get the first experience of implementing the accordion in GEANT4 (G4), and to get the first ideas about possible performance.

About 57,000 volumes represent the pieces of the barrel accordion calorimeter in this code. Though the basic accordion shapes are reproduced, the geometry description is very preliminary in this version. The G4Box shape of the flat parts should be changed to trapezoids, absorbers with thin Pb should be inserted (for eta>0.8), round corners will be totally resigned, ...

Performance

The first estimate of the CPU time: 0.4 sec per GeV during EM shower simulation. Only the tracking part of G4 implementation is tested so far. Simulation of hits and digitization is not included in this version.

It takes almost 2 min to start a run and about 1 min to finish it.

The tracking part of EM shower simulation in GEANT3 (in ACCBGEO only) takes 0.55 sec per GeV on the same processor with the cuts used for physics TDR production (0.1 MeV), and 0.34 sec per GeV with default cuts (1 MeV).

These numbers and this comparison are VERY PRELIMINARY and more understanding of comparable cuts in G3 and G4 will be needed.

Processor used: 400 MHz Pentium processor i686, Linux 5.1, g++ with optimization: GCC -O [specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/egcs-2.91.66/specs gcc version egcs-2.91.66 19990314 (egcs-1.1.2 release)]

Total memory: 386 Mbyte. This G4 version of the barrel accordion used 30.5% of total memory, ACCBGEO in G3 used only 1.2% of it.

EM processes are described as in the standard G4 example $G4INSTALL/examples/novice/N02/src/ExN02PhysicsList.cc. This Physics List should be extended in the following versions.

For data output the RecorderBase class is used. It provided by Bill Seligman from Columbia University, Nevis Labs. See his commments in RecorderBase.hh. A record may take the form of histograms, or ntuples, or entries in a database. If one uses a Recorder class, than all the record-keeping details are kept in a single class instead of being spread out among many different classes.


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