Vienna, December 2009
paul.buehler@oeaw.ac.at

Due to evaporation of the target material, outgasing of the beam tubes, and
limited pumping speed the beam tube in the vicinity of the target is not empty.
The remaining gas, which mainly consist of Hydrogen and Nitrogen, has an
integrated density (along the z-axis) of a few percent of the target density. It
therefore behaves like a secondary target. Its density profile is peaked
approximately at the nominal target position but is spread over several meters.

This package includes a new class PndRestGas and modifications to the event
generators (evntgen, dpm, urqmd) which allow to simulate the distribution of the
main vertex according to the rest gas distribution in the beam tube. ASCII files
with computed density distributions for Hydrogen and Nitrogen are provided.


. Files affected by these modifications:

  pgenerators/CMakeLists.txt
  pgenerators/PGenLinkDef.h
  pgenerators/PndDpmDirect.cxx
  pgenerators/PndDpmDirect.h
  pgenerators/PndUrqmdSmmGenerator.cxx
  pgenerators/PndUrqmdSmmGenerator.h
  generators/FairEvtGenGenerator.cxx
  generators/FairEvtGenGenerator.h

. New files

  pgenerators/PndRestGas.cxx
  pgenerators/PndRestGas.h
  input/H_densityprofile.txt
  input/N_densityprofile.txt


. New class PndRestGas:

  - reads data from a two-column ASCII file
  - provides a rest gas density profile function


. Modifications:

  - pgenerators/PndDpmDirect
 
    - new constructor with (Mom,Mode,Rsigma,DensityFunction)
		- main vertices are distributed in x/y-plane with a gaussian profile with
			sigma=Rsigma and along the z-axis according to the rest gas density
			profile function DensityFunction
	  - TF1* DensityFunction can be obtained with help of the PndRestGas class
	 
	  example:
	
	  // get gas density function
		char s1[80] = gSystem->Getenv("VMCWORKDIR");
	  char s2[80] = "/input/H_densityprofile.txt";
		PndRestGas *DD = new PndRestGas(strcat(s1,s2));
	  TF1* DDFun = DD->GetDDFun();
	
    // define event generator
		PndDpmDirect *dpmGen=new PndDpmDirect(p,mode,0.1,DDFun);
    primGen->AddGenerator(dpmGen);
		


  - pgenerators/PndUrqmdSmmGenerator
		
    - new constructor with const (fileName,Rsigma,DensityFunction)
		- main vertices are distributed in x/y-plane with a gaussian profile with
			sigma=Rsigma and along the z-axis according to the rest gas density
			profile function DensityFunction
	  - TF1* DensityFunction can be obtained with help of the PndRestGas class
	 
	  example:
	
	  // get gas density function
	  char s1[80] = gSystem->Getenv("VMCWORKDIR");
	  char s2[80] = "/input/H_densityprofile.txt";
		PndRestGas *DD = new PndRestGas(strcat(s1,s2));
	  TF1* DDFun = DD->GetDDFun();
	
    // define event generator
    PndUrqmdSmmGenerator* urqmdGen = new PndUrqmdSmmGenerator(urqmdFile.Data(),0.1,DDFun);
    primGen->AddGenerator(urqmdGen);
		


  - generators/FairEvtGenGenerator
		
    - new constructor with const (fileName,Rsigma,DensityFunction)
		- main vertices are distributed in x/y-plane with a gaussian profile with
			sigma=Rsigma and along the z-axis according to the rest gas density
			profile function DensityFunction
	  - TF1* DensityFunction can be obtained with help of the PndRestGas class
	 
	  example:
	
	  // get gas density function
	  char s1[80] = gSystem->Getenv("VMCWORKDIR");
	  char s2[80] = "/input/H_densityprofile.txt";
		PndRestGas *DD = new PndRestGas(strcat(s1,s2));
	  TF1* DDFun = DD->GetDDFun();
	
    // define event generator
    FairEvtGenGenerator* evtGen = new FairEvtGenGenerator("output.evt",0.1,DDFun);
    primGen->AddGenerator(evtGen);
		


. new input files
  
	- input/*_densityprofile.txt

    - Two column ASCII file (zval / density)
		- zval is distance from nominal target position along z-axis in units of mm
			(<0: upstream, >0: downstream)
	  - densities are given in units of ??


. modifications are contained in tar-file
tar -cvf PndRestGas_091217.tar \
README \
-C $VMCWORKDIR \
pgenerators/CMakeLists.txt \
pgenerators/PGenLinkDef.h \
pgenerators/PndRestGas.cxx \
pgenerators/PndRestGas.h \
pgenerators/PndDpmDirect.cxx \
pgenerators/PndDpmDirect.h \
pgenerators/PndUrqmdSmmGenerator.cxx \
pgenerators/PndUrqmdSmmGenerator.h \
generators/FairEvtGenGenerator.cxx \
generators/FairEvtGenGenerator.h \
input/H_densityprofile.txt \
input/N_densityprofile.txt
gzip -v PndRestGas_091217.tar