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BetafuncEvtVtxGenerator.cc

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// $Id: BetafuncEvtVtxGenerator.cc,v 1.8 2008/04/04 21:38:25 yumiceva Exp $
/*
________________________________________________________________________

 BetafuncEvtVtxGenerator

 Smear vertex according to the Beta function on the transverse plane
 and a Gaussian on the z axis. It allows the beam to have a crossing
 angle (slopes dxdz and dydz).

 Based on GaussEvtVtxGenerator
 implemented by Francisco Yumiceva (yumiceva@fnal.gov)

 FERMILAB
 2006
________________________________________________________________________
*/



#include "IOMC/EventVertexGenerators/interface/BetafuncEvtVtxGenerator.h"
#include "FWCore/Utilities/interface/Exception.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"

#include "CLHEP/Random/RandGaussQ.h"
#include "CLHEP/Units/SystemOfUnits.h"
#include "CLHEP/Units/PhysicalConstants.h"
//#include "CLHEP/Vector/ThreeVector.h"
#include "HepMC/SimpleVector.h"

#include <iostream>



BetafuncEvtVtxGenerator::BetafuncEvtVtxGenerator(const edm::ParameterSet & p )
: BaseEvtVtxGenerator(p)
{ 
  
  fRandom = new CLHEP::RandGaussQ(getEngine());

  fX0 =        p.getParameter<double>("X0")*cm;
  fY0 =        p.getParameter<double>("Y0")*cm;
  fZ0 =        p.getParameter<double>("Z0")*cm;
  fSigmaZ =    p.getParameter<double>("SigmaZ")*cm;
  alpha_ =     p.getParameter<double>("Alpha")*radian;
  phi_ =       p.getParameter<double>("Phi")*radian;
  fbetastar =  p.getParameter<double>("BetaStar")*cm;
  femittance = p.getParameter<double>("Emittance")*cm; // this is not the normalized emittance
  fTimeOffset = p.getParameter<double>("TimeOffset")*ns*c_light; // HepMC time units are mm
 
  if (fSigmaZ <= 0) {
          throw cms::Exception("Configuration")
                  << "Error in BetafuncEvtVtxGenerator: "
                  << "Illegal resolution in Z (SigmaZ is negative)";
  }

  
}

BetafuncEvtVtxGenerator::~BetafuncEvtVtxGenerator() 
{
    delete fRandom; 
}


//Hep3Vector* BetafuncEvtVtxGenerator::newVertex() {
HepMC::FourVector* BetafuncEvtVtxGenerator::newVertex() {

        
        double X,Y,Z;
        
        double tmp_sigz = fRandom->fire(0., fSigmaZ);
        Z = tmp_sigz + fZ0;

        double tmp_sigx = BetaFunction(tmp_sigz,fZ0); 
        X = fRandom->fire(0.,tmp_sigx) + fX0; // + Z*fdxdz ;

        double tmp_sigy = BetaFunction(tmp_sigz,fZ0);
        Y = fRandom->fire(0.,tmp_sigy) + fY0; // + Z*fdydz;
          
        //if (fVertex == 0) fVertex = new CLHEP::Hep3Vector;
        //fVertex->set(X, Y, Z);
        if ( fVertex == 0 ) fVertex = new HepMC::FourVector();
        fVertex->set(X,Y,Z,fTimeOffset);
                
        return fVertex;
}

double BetafuncEvtVtxGenerator::BetaFunction(double z, double z0)
{
        return sqrt(femittance*(fbetastar+(((z-z0)*(z-z0))/fbetastar)));

}


void BetafuncEvtVtxGenerator::sigmaZ(double s) 
{ 
        if (s>=0 ) {
                fSigmaZ=s; 
        }
        else {
                throw cms::Exception("LogicError")
                        << "Error in BetafuncEvtVtxGenerator::sigmaZ: "
                        << "Illegal resolution in Z (negative)";
        }
}

TMatrixD* BetafuncEvtVtxGenerator::GetInvLorentzBoost() {

        //alpha_ = 0;
        //phi_ = 142.e-6;
        
        if (boost_ != 0 ) return boost_;
        
        //boost_.ResizeTo(4,4);
        //boost_ = new TMatrixD(4,4);
        TMatrixD tmpboost(4,4);
        
        //if ( (alpha_ == 0) && (phi_==0) ) { boost_->Zero(); return boost_; }
        
        // Lorentz boost to frame where the collision is head-on
        // phi is the half crossing angle in the plane ZS
        // alpha is the angle to the S axis from the X axis in the XY plane
        
        tmpboost(0,0) = 1./cos(phi_);
        tmpboost(0,1) = - cos(alpha_)*sin(phi_);
        tmpboost(0,2) = - tan(phi_)*sin(phi_);
        tmpboost(0,3) = - sin(alpha_)*sin(phi_);
        tmpboost(1,0) = - cos(alpha_)*tan(phi_);
        tmpboost(1,1) = 1.;
        tmpboost(1,2) = cos(alpha_)*tan(phi_);
        tmpboost(1,3) = 0.;
        tmpboost(2,0) = 0.;
        tmpboost(2,1) = - cos(alpha_)*sin(phi_);
        tmpboost(2,2) = cos(phi_);
        tmpboost(2,3) = - sin(alpha_)*sin(phi_);
        tmpboost(3,0) = - sin(alpha_)*tan(phi_);
        tmpboost(3,1) = 0.;
        tmpboost(3,2) = sin(alpha_)*tan(phi_);
        tmpboost(3,3) = 1.;

        tmpboost.Invert();
        boost_ = new TMatrixD(tmpboost);
        //boost_->Print();
        
        return boost_;
}

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