[G12] gsim feedback study

[Craig Bookwalter]

  g12ers,
     This is an update on the 
taking-real-CLAS-data-and-feeding-it-through-GSIM study. I've fixed my 
previous error with the vertex for events going into GSIM--they now go 
into GSIM with the PART sector 0 vertex for each track set to the MVRT 
vertex from the real data. I also correct by hand the ttag and tpho of 
the input TAGR bank to the event vertex. I do not smear with GPP. These 
changes combine to give only about a 10% return. Before the vertex fix I 
was getting 4500/8100 events or so reconstructed, now I am getting about 
5300/8100. I looked at 50 events with bosdump and CED and found 20 out 
of these 50 were not identified as p pi+ pi- events. From these 20, the 
following problems were identified:

* 9 events where an incorrect number of hit-based tracks were found. 
This happens for various reasons--multiple scattering in the target 
(most cases), or a lack of in-time DC hits (happened a few times), or a 
lack of DC hits at all (happened a few times). Also, R1 hits seem to be 
almost always marked as out-of-time by ced.
* 5 events where a track struck the TOF with a reasonable time, but an 
adjacent paddle was hit at a much later time, and the SCRC bank 
reconstructs it into a "cluster" with some weighted average between 
those two times. The average pulls the once-reasonable time of the 
primary TOF hit up, resulting in pi's being cast adrift in the mass 
region between pions and kaons (PID == 0) or shifted all the way to 
being called K's. Protons get shifted into the deuteron region.
* 4 events with missing time-based tracks, usually because there is no 
good TOF hit to associate with the track (ie the paddle didn't fire).
* 2 events where the TOF times were just too large to give the correct 
PID--perhaps the track hits a dead paddle and produces a secondary that 
fires the adjacent paddle.

Draw what conclusions ye will. I think it would be foolish to pursue 
this 95% number without more information on the study that got this 
number, ie what ffread cards were being passed to GSIM, whether or not 
GPP was used and if so how, etc.

I welcome any comments.

--cb