Geometry & Materials

Simulation

1. select a file name for the root output:

   	//=======================================================================
   	//  Create the output file
   	sprintf(filename,"myfilename.root");
   	

2. Define your event generator and simulations parameters:

            AliGenCocktail *gener = new AliGenCocktail(); // Cocktail class
            gener->SetPtRange(.02,10.00);                 // Transverse momentum range   
            gener->SetPhiRange(180.,360.);                // Azimuthal angle range  
            gener->SetYRange(-0.25,0.25);                 // Pseudorapidity range
            gener->SetOrigin(0,0,0);                      // Vertex position
            gener->SetSigma(0,0,5.6);                     // Sigma in (X,Y,Z) (cm) on IP position
            gener->Init();                                // Initialize the generator
   	

3. Select the detector seen by the tracking:

            Int_t iPHOS=1;    // PHOS is in
            Int_t iPMD=0;     // PMD  is out
   	

4. Create a PHOS object (GPS2 is so far the unique configuration option, see below):

    
            if(iPHOS) {
            //=================== PHOS parameters =========================== 
            AliPHOS *PHOS  = new AliPHOSv0("PHOS","GPS2");
   	

You van now run the simulation by entering the following command at the aliroot prompt:

       aliroot> gAlice->Run(1,"PHOSConfig_Central.C");  
    

Geometry

Definition

The class AliPHOSv0 ( inheritance tree ) describes this geometry. We have defined also a class AliPHOSv1 ( inheritance tree ) which in addition contains the photodiode response and the light transport through the crystal.

The parameters of the geometry are given in class AliPHOSGeometry ( inheritance tree )

Figure 1.a: GEANT Tree which describes the EMC-PHOS geometry

Figure 1.b: GEANT Tree which describes the PPSD-PHOS geometry

Implementation

Figure 2.: Class diagram for the geometry/simulation package

AliPHOS: This is the base class. It derives from AliDetector. It's only purpose is to describe the materials (à la AliMC) needed for the EMCA and PPSD construction.

AliPHOSv4: It derives from AliPHOS.

• It sets up the geometry for the Root display (AliPHOSv4::BuildGeometry()) and for the GEANT tracking (AliPHOSv4::CreateGeometry()).
• It watches the tracks passing through the active media of EMCA and PPSD (AliPHOSv4::StepManager()).
• It stores the hits (AliPHOSv4::AddHit()), using the AliPHOSHit class.
• It stores the digits (AliPHOSv4::FinishEvent()), using the AliPHOSDigit class.

AliPHOSv1 : derives from AliPHOSv0 and includes the light transport in the crystal and the response of the PIN photodiode à la O. H. Oddland.

AliPHOSvFast : used for fast simulation.

AliPHOSGeometry : It derives from TObject to make it persistent. It is a singleton, i.e., a pointer to the unique instance of this class is obtained by:

        AliPHOSGeometry * Geom = AliPHOSGeometry::GetInstance()
      

• It sets the various parameters for the geometry description and provides the method to access all the parameters. To avoid cumbersome macros at run time these parameters can only be changed manually in the source code.
• It provides the method to convert the absolute detector Id (crystal in EMCA or pad in PPSD) into a relative Id : PHOS module number, PPSD module number, row, column (AliPHOSGeometry::AbsToRelNumbering()) and the reverse operation (AliPHOSGeometry::RelToAbsNumbering()).
• It provides the method to convert an absolute Id into a three-vector giving the position of the detector in ALICE (AliPHOSGeometry::RelPosInAlice()).

AliPHOSHit: It derives from AliHit. It stores the hits as the pair (absolute Id, deposited energy). The hits presently are stored in the hit TTree as one hit per elementary cell (EMC crystal or PPSD gas cell) (See the the AddHit() method in AliPHOSv0).

AliPHOSDigit : It derives from AliDigit. It stores the digits as the pair (absolute Id, energy) in the digit TTree (see the FinishEvent() method in AliPHOSv0).

Usage

     Int_t iPHOS=1;
     if(iPHOS) {
     AliPHOS * phos = new AliPHOSv4("PHOS", char * name) ;
    

• GPS2: will create EMCA plus PPSD
  
  Figure 3a.: ROOT Display of ALICE: All Views

  Figure 3b.: ROOT Display of ALICE: Front Views

  Figure 3c.: ROOT Display of ALICE: All View3

  Figure 4.a: ROOT Display of ALICE: zoom on PPSD, Front Views

  Figure 4.b: ROOT Display of ALICE: zoom on PPSD, Perspective View

  
  
  
• more to come from Protvino (EMCA plus other CPV type)

Result