Aliroot simulation
The use of aliroot program allows to include the specific functions
written for digitisation in SSD. In this way the digitisation
functions for the ITS SSD can be also tested. The general idea is to
use as much as possible the classes and the function written for
ITS.
The way choosed is to implement a new
class on the model of AliITSvPPRasym and AliITSv5asym classes from
AliITS, called AliBeam, to introduce the Beam test geometry. In this
first step the geometry include only the tested SSD whitout any
telescope nor structures. As in the Geant simulation the materials
"air" and "silicium" is created from the standard ITS material.
A new object AliBeam can be managed by aliroot. The file
ConfigBeam.C sets the Geant simulation and can be called as
usually by grun.C. The hits produced
are transformed into digits via the macro AliBeamHits2Digits.C.
The aliroot version used is v3-09-04 with root 3.03/09.
Class implementation
CreateMaterials
This function read the material from the file
Euclid/ITSgeometry_5asymm.tme. This file describes the
materials and traking mediums for the ITS and is already
present. To read the file the function AliModule::ReadMaterial is
called. The class AliITS is derived from AliModule.
CreateGeometry
This function fills the Geant common block with the geometry.
The first implementation uses the functions TGeant3::Gsvolu and
TGeant3::Gspos which are similar to the subroutines GSVOLU and GSPOS
of Geant3. A second implementation will read the file
Euclid/BeamTestGeometry.euc by the function
AliModule::ReadEuclid. Actually the first implementation is used for
the simplest geometry with one SSD module only, while the
Euclid/BeamTestGeometry.euc file describes also the volumes of
the telescopes. A future developemnt will introduce a flag which allow
switching between the two version run-time without any othe problem of
inizialization.
InitGeometry
The complex structure of ITS needs the support of AliITSgeom class to
identify the modules. The more important aim of this function is to
inizialize the class member fITSgeom which remember the position of
all modules in terms of layer and ladder. The class member fITSgeom
is called by some functions of AliITS class in the digitization.
In the simplest case the number of each the layer and the ladder is
set to one.
Beam test simulation
A first test with 1000 events and a beam of plus pion at 50 Gev gives
this result in terms of position and momentum along
y assix. The positions of the hits along the y assix correspond to the
geant entering and outgoning hits; the energy lost at this second is
the energy loss in all the volum.
The resutl in term of energy loss is
analog to the Geant result. For more information about the resuts see
data analysis.
Hits to digits
The hits produced by simulation are converted into digits calling the
function AliITS::HitsToDigits already presents.
page created by Federica
Benedosso
Last change 28.IV.2003