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The geometry for the Monte Carlo is found in the repository under programs/Simulation/hdds. The description of the geometry is written in xml format. The programs hdds-geant and hdds-root translate these xml based geometry into fortran code for GEANT3 and C code for root, respectively.


  1. The latest CDC geometry modification implemented a downstream gas plenum of 2.54cm thickness with an aluminized mylar window. The position of the 28 layers of straws are modeled according to the latest numbers with straws of 1.6025cm outer diameter including tolerances. The outer aluminum shell of the CDC is 2mm thick with an OD of about 4cm smaller than the end plates. 12 aluminum support rods are located outside the gas volume of the CDC between the end plates. The gas volume is an Ar/CO2 mixture. The downstream end plate is carbon fiber with 6mm thickness while the downstream gas plenum is 2.54cm thick. The upstream end plate is from Aluminum and 12.5mm thick with an upstream gas plenum of 6.99mm thickness. Some pictures with explanations about the CDC geometry as of April 09 is found here.