README July 21, 2008 CDC layer configuration simulation study


This study contains two alternate CDC geometries. Both come from
XML files supplied by Beni Zhilman, their origins below.

The study was done based on svn revision 3941.

close_packed:
e-mailed on July 22th, 2008 at 10:15am 
as attachment named "CentralDC_HDDS.xml_27layers"

phase_shifted:
e-mailed on July 18th, 2008 at 10:44am
as attachment name "CentralDC_HDDS.xml_layers_shifted:


The second uses the nominal design from GlueX-doc-990 but
with relative phi-angle shifts in the axial CDC layers.
The shifts were supplied by me (David) in an e-mail to Beni
below of which is the important snippet:

layer  1 shift:   0.000 milliradians (+0.000 degrees)
layer  2 shift: +62.832 milliradians (+3.600 degrees)
layer  3 shift: -36.744 milliradians (-2.105 degrees)
layer  4 shift:   0.000 milliradians (+0.000 degrees)
layer  5 shift:   0.000 milliradians (+0.000 degrees)
layer  6 shift:   0.000 milliradians (+0.000 degrees)
layer  7 shift:   0.000 milliradians (+0.000 degrees)
layer  8 shift: + 3.771 milliradians (+0.216 degrees)
layer  9 shift:   0.000 milliradians (+0.000 degrees)
layer 10 shift: +28.050 milliradians (+1.607 degrees)
layer 11 shift: -17.600 milliradians (-1.008 degrees)
layer 12 shift: + 9.973 milliradians (+0.571 degrees)
layer 13 shift:   0.000 milliradians (+0.000 degrees)
layer 14 shift:   0.000 milliradians (+0.000 degrees)
layer 15 shift:   0.000 milliradians (+0.000 degrees)
layer 16 shift:   0.000 milliradians (+0.000 degrees)
layer 17 shift:   0.000 milliradians (+0.000 degrees)
layer 18 shift: +18.265 milliradians (+1.047 degrees)
layer 19 shift: -11.701 milliradians (-0.670 degrees)
layer 20 shift: + 6.756 milliradians (+0.387 degrees)
layer 21 shift: - 4.651 milliradians (-0.266 degrees)
layer 22 shift: + 2.856 milliradians (+0.164 degrees)
layer 23 shift: - 2.335 milliradians (-0.134 degrees)
layer 24 shift: + 1.727 milliradians (+0.099 degrees)


These values were obtained using the following where dphi is
the angle spanned by a single straw tube for the layer. Note
that for stereo wires, a phase shift of 0 is imposed independent
of this code block.

   switch((layer-1)%8){
       case 0: shift =       0.0;    break;
       case 1: shift = +dphi/2.0;    break;
       case 2: shift = -dphi/3.0;    break;
       case 3: shift = +dphi/5.0;    break;
       case 4: shift = -dphi/7.0;    break;
       case 5: shift = +dphi/11.0;    break;
       case 6: shift = -dphi/13.0;    break;
       case 7: shift = +dphi/17.0;    break;
   }