CentralDC_HDDS.xml: The CDC geometry with closed packing of the axial layers.
                    27 layers in total with the following configuration of
                    layers from the inside out:
                    4 axial, 4 stereo (2x+6, 2x-6), 4 axial, 
                    4 stereo (2x+6, 2x-6), 8 axial, 3 stereo (3x+6)