Changes for new release of E614 GEANT version 1.3

                       D.H. Wright     April 2000


  A. Summary

        E614 GEANT now uses look-up tables to get drift times as a function
     of track position in the cell.  In the previous version the cell entry
     and exit positions and directions were stored from which a local helix 
     was approximated.  The point of closest approach to the wire was then
     calculated assuming circular drift time contours.  The new version 
     stores the track location at intervals of 180 microns (the mean 
     distance between charge clusters in DME) and for each of those points
     looks up the drift time from a table calculated by GARFIELD for DME 
     gas at B = 2.2T.  The smallest of the cluster drift times is recorded 
     as the leading edge time in the TDCs.  This approach makes no 
     assumption about the track curvature or the shape of the drift 
     isochrones.  New isochrone files will be required if there are changes
     in B, E, pressure or temperature.  

  B. Files changed in new release

     1. store_track_segments.F - store (x,y,z) in local cell coordinates and
                      momentum and time-of-flight at every step.

     2. define_data_format.F - increased number of quantities stored 
                      to 308 (enough to accommodate 61 hits)

     3. digitize_dc.F - remove ypoca as means of calculating smallest drift
                      time.  Replace with look-up table.
 
     4. digitize_pc.F - same changes as for digitize_dc.F.  The current
                      look-up table is not real - just something to use until
                      GARFIELD calculation is done.

     5. uginit.F - add calls to new routines read_dc_isochrones.F and
                      read_pc_isochrones.F which read in GARFIELD drift time
                      files

     6. e614.com - add logicals to define GARFIELD isochrone files

     7. Makefile - removed calc_helix.o, drift_distance_to_time.o, ypoca.o .
                      Added dc_cluster_time.o, pc_cluster_time.o, 
                      read_dc_isochrones.o, read_pc_isochrones.o, 


  C. Files added:

     1. dc_cluster_time.F - finds point with smallest drift time within a
                      cluster segment in drift cell

     2. pc_cluster_time.F - finds point with smallest drift time within a
                      cluster segment in proportional cell

     3. isochrone_data.inc - 201 x 201 element arrays containing drift times 
                      for DCs and PCs at 10 micron intervals

     4. isochrone_data.par - sets the size of the above arrays

     5. read_dc_isochrones.F - reads drift cell drift times from file into
                      array 

     6. read_pc_isochrones.F - reads proportional cell drift times from file 
                      into array

     7. hit_elements.par - define number of elements per hit to be stored  


         
  D. Files deleted:

     1. drift_distance_to_time.F - this is now done by look-up table

     2. ypoca.F - we no longer calculate point of closest approach

     3. calc_helix.F - don't need to approximate helix any more



  E. Flow charts for GEANT user hooks

     1.                       GUDIGI
                                |
               -------------------------------------
               |                |                  |
           DIGITIZE_DC      DIGITIZE_PC     SIMULATE_1877_TDC
               |                |
               |                |
         DC_CLSTER_TIME   PC_CLUSTER_TIME




     2.                       GUSTEP
                                |
                    -------------------------
                    |                       |
                SPIN_PROP          STORE_TRACK_ELEMENTS




     3.                       GUFLD
                                |
                           B_FIELD_INT




     4.                      UGINIT
                                |
           ---------------------------------------------------------------
           |      |       |        |        |           |
        DEFCAR  APFFKY  UGMATE  UGSTMED  BFLDMAP  READ_DC_ISOCHRONES


        ------------------------------------------------------------------
               |               |          |                 |
        READ_PC_ISOCHRONES   UGEOM  CALC_WIRE_POS   DEFINE_DATA_FORMAT  

      
        ------------------------------------------------------------------
          |          |            |          |          |          |
        UHINIT  READ_TDCMAPS  YBOS_INIT  YBOS_MAKE  FILL_EVID  FILL_TDCP  


        -----
            |
        YBOS_WRITE




     5.                      UGLAST
                                |
                    --------------------------
                    |           |            |
                FILL_EVID   YBOS_WRITE   YBOS_EXIT




     6.                       UGEOM
                                |
             -----------------------------------------------
             |            |          |          |          |
       CHAMBER_GEOM  DRIFT_GEOM  PROP_GEOM  TARG_GEOM  SCINT_GEOM
             |
        OPEN_MCGEOM
             |
       READ_DET_GEOM 



      
     Other user hooks (self-contained):

         GUKINE, GUTREV, GUTRAK, GUDCAY, GUOUT, GUHADR, GUPHAD