New Drift Chamber Geometry setup in bbsim : DchSimGeom
E. Lamanna, M. Posocco, S. Rahatlou
Last Update: September 5,'97
This page contains informations on the package DchSimGeom dedicated to the definition of the geometry of the BaBar drift chamber in bbsim.
The present design of the BaBar drift chamber gives the following main characteristics of the detector:
- Cylindrical barrel of lenght 3.28 m, inner radius 23.6 and outer 80.9 cm, including the rear electronic material ;
- Flat end plates;
- 10 Super Layers: 4 axial, 3 stereo U and 3 stereo V;
- 4 layers in each Super Layer for a total of 40 layers;
- Hexagonal cells in the layers;
- Cell defined through one 20 micron sense wire and in each Super Layer:
- six 120 micron field wires for the two centered layers;
- five 120 micron field wires and two 80 micron control wires for the edge layers;
- The total number of cells is 1776 : (96+112+128+144+176+192+208+224+240+256)*4;
- In each Super Layer all the wires have same twist angle but different stereo angles for different radius;
- The total number of wire is 7104 + 14208 + 7104.
All these characteristics prevent from using the Geant approach to define in detail the detector ( up to the definition of the cells) through volumes. We have choosen a different approach to simulate the propagation of the particles in the detector,
similar to those used for the KLOE drift chamber. In the new implementation we use an hybrid solution:
The first version of DchSimGeom was prepared:
- to setup the full structure of the data base;
- to define completely the materials and the geometry;
- to define the Hit structure;
- to give an accurate geometric response using a multistep tracking approach of the particles in the cell (a fixed minimum step is selected when the particle crosses the Super Layers).
It will be used for the quality control of the semianalitycal approach which will follow (necessary to speed up the simulation).
The current release includes the following files:
Standard Geometry
The standard Geant geometry of the drift chamber is defined through the declaration of materials ( Air, Aluminium, Carbon Fiber, Nomex, Tungsten,
Silicium and a mixture of He and Isobutane) and volumes.
The basic components of the chamber are: forward and backward end plates, inner and outer walls, Super Layers.
The routines DchMatDef.F and DchVolDef.F, declare the media and the volumes in Geant.
Two levels of debug may be used to print the defined volumes calling the routines DchDebVol.F and DchVolDump.F.
The response of the detector is simulated in the Geant Hit structure defining the Super Layers as sensitive detectors and storing in the hit banks all
the values computed during the tracking of the particles in the medium.
The detectors and the hit structure are defined in the routine DchDetDef.F.
All the parameters necessary to store the drift chamber materials, media and volumes are input in bbsim using a dbio database dch.db.
Cell definition
The full structure is defined storing the parameters of the 7 (8) cell wires. The position and the angles of the first cell is used to make all the
other cells in the same layer. The Adam's hex2 file have been used to output all the relevant wire parameters . These parameters, describing for each layer the wires of the first cell, are included in four templates filled in dch.db.
Dedicated tools have been studied to generate run time the wire geometry and to evaluate the hits informations when a particle crosses the cell:
- DchFindCell() Find the layer and the cell using the current position X,Y,Z of the particle;
- DchCellEplt() Find the cell number looking at the Rear End Plate;
- DchPwirEplt() Get the wire phi at the rear endplate;
- DchRwirEplt() Get the wire radius at the rear endplate;
- DchTwirEplt() Get the wire twist at the rear endplate;
- DchPhiWir() Find the wire phi in the plane Z=Const;
- DchRwir() Find the wire radius in the plane Z=Const;
- DchWirEqu() Estimate the equations of the selected wire;
- DchCWirEqu() Estimate the equations of all the wires in the selected cell;
- DchWirDis() Evaluate the distance of the selected wire from the selected point;
The Reference System used to evaluate the geometry responce of the chamber is centered in the Gas volume and its Z axis is superimposed to the axis of
the cilynder.
The names of the wires in the cell are assigned following the M. Kelsey BaBar note # 331.
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Cell response
The response of the Drift chamber to the crossing of charged particle is evaluated in the routine DchStep.F, called when a particle
crosses the sensitive Super Layers.
The hits are evaluated during the tracking of the particles in each cell. For each particle crossing a cell one hit will be stored and Energy loss and multiple scattering both in the gas and in the wires will be taken into account.
A typical B0-B0~ in the chamber may be seen as response of GEANT . The response of the chamber using the cells and wires in the new code is also available. Go Back
Package coordinator: Ernesto Lamanna
Maintained by Ernesto Lamanna, Mario Posocco, Shahram Rahatlou
E-mail lamanna@roma1.infn.it 39-6-49914232 and E-mail posocco@padova.infn.it, Tel. 39-49-8277094 E-mail
rahatlou@roma1.infn.it, Tel. 39-6-49914232
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