Notes on new shower track philosophy
G. Eppley and P. Nevski
New versions of GSTAR and G2T were released on Feb. 10, 1997
containing a new treatment of secondary tracks. The definition if
shower tracks in the GSTAR document, STAR note 235, p 11, is now obsolete.
There is no longer a distinction between the way shower tracks and
secondary tracks are handled in the G2T event tables. In general,
it is undesirable to save all the secondary tracks produced in dense
material in the detector because of space considerations in the eventrecord.
Most of these secondary particles never interact with sensitive material
in the detector. It is, however, often desirable to be able to determine
the origin of hits from secondary tracks.
Normally GEANT places secondary tracks in a temporary stack and does not
write them out. The new version of GSTAR appends any secondary track
which produces a hit in a specified detector (see detailed example
below) to the output KINE bank. In the output g2t_track table, start_vertex_p
points to the starting vertex of the track in g2t_vertex for both primary
tracks and for secondaries that have been saved. In the g2t_vertex table,
parent_p points to zero in the case of primary tracks or to the closest
saved ancestor track in the case of secondary tracks. If the
intervening tracks and vertices have not been saved (as in a shower
in non sensitive material), the vertex is displaced in space from the ancestor
track and is_shower = 1 in g2t_track.
It is also possible to save secondary tracks whether or not they produce
hits. This is achieved with the following commands:
MODE TRAC SIMU 2
DETP TRAC proc rmax zmax epar epro
where proc =
GEANT process (see PHYS001-3) or ALL
rmax, zmax =
outer limits for saving secondaries, (cm)
epar, epro = minimum energy
for PARent and secondary (PROduct), (GeV)
The default setting in gstar_example.scr is
MODE TRAC SIMU 2
DETP TRAC DCAY 220. 270. 0. 0.
The following command determines whether hits are saved and whether
secondary tracks producing hits are saved:
MODE dete SIMU n
where dete = GSTAR subdetector, e.g. TPCE
n = 0, no
1, hit production
2, hit production and secondary tracks producing hits are saved
The default setting in gstar_example.scr is:
MODE TPCE SIMU 2
MODE FTPC SIMU 2
MODE SVTT SIMU 2
MODE BTOF SIMU 2
As a result of the above setting, a secondary track that produces
a hit in any of the specified detectors will be saved.
Historically, next_parent_p in g2t_track pointed to the closest saved ancestor
track in the case of tracks with is_shower = 1. (There was no entry in
g2t_vertex.) This pointer has been retained temporarily for secondary tracks.
It will be dropped in a subsequent release of G2T since two different ways
of finding the ancestor track are not necessary.