update to HDGeant

[Richard Jones <richard.t.jones@uconn.edu>]

Dear colleagues,

After taking a look at the model of the Central Drift Chamber (CDC) that 
Curtis brought to the
November meeting, I knew that my geometry model had the stereo layers 
put in wrong.  Since
then Curtis sent me a program that he used to determine the drilling 
hole positions in the end
plates, which I used to correct the Hall D geometry model.  Unlike 
before when I tried to use
the description in HDFast.db to guess what it was supposed to look like, 
now the layers actually
fit without straws overlapping each other.  I have checked in the new 
geometry into cvs.  To get
it you can just do cvs checkout hdds.  There are now 23 layers instead 
of 22, the stereo layers
are in a different order, and so on.  Basically things have changed.

At the meeting I also learned that the cathode strips the HDFast.db has 
on the inner and outer
CDC windows are not currently a part of the design.  I see that they are 
still defined in the HDFast
geometry.  Has someone checked to see what happens to our polar angle 
resolution when these
are removed?  I am not suggesting that we put them back in, but just 
asking if the resolution studies
are consistent with the current detector design.  If so then it would be 
helpful to get the working
version of HDFast.db into cvs so we are all looking at the same detector 
description.

In response to a request from Dave Doughty, I have added a new track 
parameter to the <point>
and <shower> tags.  They are there to aid in the development of 
reconstruction code by giving
the "true" values of the track/plane intersections and shower 
coordinates.  From the track="int"
parameter you can tell which points go together when stitching track 
segments together.  The
track number is just the number that Geant assigns to a final-state 
particle at the beginning of
an event, and gets inherited by all of its secondaries.  Yes, photons 
have "track" numbers too.

To get and run the new code, you need to cvs update your hddm and 
HDGeant areas in cvs
and rebuild hdgeant from sources.

Richard Jones