[Halld-offline] updates to tracking and hdgeant

[Simon Taylor]

Dear offliners,

We have recently updated the default solenoid field map from -1500 A to 
+1350 A.  Unfortunately, for the automated reconstruction jobs this lead 
to a conflict between the field being used for the simulation and the 
one used for the reconstruction.  Furthermore, in the reconstruction the 
algorithm for determining the charge implicitly depended on the sign of 
Bz.  As a consequence the b1pi twice-weekly analysis has been broken for 
some time.
I have recently checked in a change to the HDGeant code to accommodate 
the recent change in JANA regarding how the magnetic field map is 
obtained (via the new "resource" mechanism, in which the field map is no 
longer stored in the ccdb database itself).  I have also made numerous 
small changes to the reconstruction code to deal with the charge 
properly.   I am happy to report that as of today the b1pi histograms 
are looking much more like previous (good) results; see for example 
https://halldweb1.jlab.org/b1pi/2014-01-30/Linux_CentOS6-x86_64-gcc4.4.6/ .  
However, if you look carefully you will see that there is a dip in 
efficiency for all charged particles near phi=0 degrees.

Simon