Gabriele Cosmo
231 lines
8.4 KiB
C++
231 lines
8.4 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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// $Id: G4SingleDiffractiveExcitation.cc 100828 2016-11-02 15:25:59Z gcosmo $
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// ------------------------------------------------------------
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// GEANT 4 class implemetation file
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//
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// ---------------- G4SingleDiffractiveExcitation --------------
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// by Gunter Folger, October 1998.
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// diffractive Excitation used by strings models
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// Take a projectile and a target
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// excite the projectile and target
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// ------------------------------------------------------------
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#include "G4SingleDiffractiveExcitation.hh"
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#include "globals.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4SystemOfUnits.hh"
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#include "Randomize.hh"
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#include "G4LorentzRotation.hh"
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#include "G4ThreeVector.hh"
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#include "G4ParticleDefinition.hh"
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#include "G4VSplitableHadron.hh"
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#include "G4ExcitedString.hh"
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#include "G4Log.hh"
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G4SingleDiffractiveExcitation::G4SingleDiffractiveExcitation(G4double sigmaPt, G4double minextraMass,G4double x0mass)
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: widthOfPtSquare(-2*sqr(sigmaPt)) , minExtraMass(minextraMass), minmass(x0mass)
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{}
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G4SingleDiffractiveExcitation::~G4SingleDiffractiveExcitation()
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{}
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G4bool G4SingleDiffractiveExcitation::
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ExciteParticipants(G4VSplitableHadron *projectile, G4VSplitableHadron *target) const
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{
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G4LorentzVector Pprojectile=projectile->Get4Momentum();
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G4double Mprojectile2=sqr(projectile->GetDefinition()->GetPDGMass() + minExtraMass);
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G4LorentzVector Ptarget=target->Get4Momentum();
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G4double Mtarget2=sqr(target->GetDefinition()->GetPDGMass() + minExtraMass);
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//G4cout << "E proj, target :" << Pprojectile.e() << ", " << Ptarget.e() << G4endl;
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G4bool KeepProjectile= G4UniformRand() > 0.5;
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// reset the min.mass of the non diffractive particle to its value, ( minus a bit for rounding...)
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if ( KeepProjectile )
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{
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//cout << " Projectile fix" << G4endl;
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Mprojectile2 = sqr(projectile->GetDefinition()->GetPDGMass() * (1-perCent) );
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} else {
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//cout << " Target fix" << G4endl;
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Mtarget2=sqr(target->GetDefinition()->GetPDGMass() * (1-perCent) );
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}
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// Transform momenta to cms and then rotate parallel to z axis;
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G4LorentzVector Psum;
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Psum=Pprojectile+Ptarget;
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G4LorentzRotation toCms(-1*Psum.boostVector());
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G4LorentzVector Ptmp=toCms*Pprojectile;
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if ( Ptmp.pz() <= 0. )
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{
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// "String" moving backwards in CMS, abort collision !!
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//G4cout << " abort Collision!! " << G4endl;
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return false;
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}
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toCms.rotateZ(-1*Ptmp.phi());
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toCms.rotateY(-1*Ptmp.theta());
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//G4cout << "Pprojectile be4 boost " << Pprojectile << G4endl;
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//G4cout << "Ptarget be4 boost : " << Ptarget << G4endl;
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G4LorentzRotation toLab(toCms.inverse());
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Pprojectile.transform(toCms);
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Ptarget.transform(toCms);
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G4LorentzVector Qmomentum;
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G4int whilecount=0;
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do {
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// Generate pt
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G4double maxPtSquare=sqr(Ptarget.pz());
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if (whilecount++ >= 500 && (whilecount%100)==0)
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//G4cout << "G4SingleDiffractiveExcitation::ExciteParticipants possibly looping"
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// << ", loop count/ maxPtSquare : "
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// << whilecount << " / " << maxPtSquare << G4endl;
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if (whilecount > 1000 )
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{
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Qmomentum=G4LorentzVector(0.,0.,0.,0.);
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//G4cout << "G4SingleDiffractiveExcitation::ExciteParticipants: Aborting loop!" << G4endl;
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return false; // Ignore this interaction
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}
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Qmomentum=G4LorentzVector(GaussianPt(widthOfPtSquare,maxPtSquare),0);
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// Momentum transfer
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G4double Xmin = minmass / ( Pprojectile.e() + Ptarget.e() );
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G4double Xmax=1.;
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G4double Xplus =ChooseX(Xmin,Xmax);
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G4double Xminus=ChooseX(Xmin,Xmax);
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G4double pt2=G4ThreeVector(Qmomentum.vect()).mag2();
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G4double Qplus =-1 * pt2 / Xminus/Ptarget.minus();
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G4double Qminus= pt2 / Xplus /Pprojectile.plus();
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if ( KeepProjectile )
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{
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Qminus = (sqr(projectile->GetDefinition()->GetPDGMass()) + pt2 )
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/ (Pprojectile.plus() + Qplus ) - Pprojectile.minus();
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} else {
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Qplus = Ptarget.plus() - (sqr(target->GetDefinition()->GetPDGMass()) + pt2 )
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/ (Ptarget.minus() - Qminus );
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}
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Qmomentum.setPz( (Qplus-Qminus)/2 );
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Qmomentum.setE( (Qplus+Qminus)/2 );
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//G4cout << "Qplus / Qminus " << Qplus << " / " << Qminus<<G4endl;
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//G4cout << "pt2 " << pt2 << G4endl;
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//G4cout << "Qmomentum " << Qmomentum << G4endl;
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//G4cout << " Masses (P/T) : " << (Pprojectile+Qmomentum).mag() <<
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// " / " << (Ptarget-Qmomentum).mag() << G4endl;
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} while ( (Ptarget-Qmomentum).mag2() <= Mtarget2 /* Loop checking, 26.10.2015, A.Ribon */
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|| (Pprojectile+Qmomentum).mag2() <= Mprojectile2
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|| (Ptarget-Qmomentum).e() < 0.
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|| (Pprojectile+Qmomentum).e() < 0. );
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//G4double Ecms=Pprojectile.e() + Ptarget.e();
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Pprojectile += Qmomentum;
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Ptarget -= Qmomentum;
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//G4cout << "Pprojectile.e() : " << Pprojectile.e() << G4endl;
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//G4cout << "Ptarget.e() : " << Ptarget.e() << G4endl;
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//G4cout << "end event_______________________________________________"<<G4endl;
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//G4cout << "Pprojectile with Q : " << Pprojectile << G4endl;
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//G4cout << "Ptarget with Q : " << Ptarget << G4endl;
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//G4cout << "Projectile back: " << toLab * Pprojectile << G4endl;
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//G4cout << "Target back: " << toLab * Ptarget << G4endl;
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// Transform back and update SplitableHadron Participant.
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Pprojectile.transform(toLab);
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Ptarget.transform(toLab);
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//G4cout << "G4SingleDiffractiveExcitation- Target mass " << Ptarget.mag() << G4endl;
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//G4cout << "G4SingleDiffractiveExcitation- Projectile mass " << Pprojectile.mag() << G4endl;
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target->Set4Momentum(Ptarget);
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projectile->Set4Momentum(Pprojectile);
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return true;
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}
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// --------- private methods ----------------------
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G4double G4SingleDiffractiveExcitation::ChooseX(G4double Xmin, G4double Xmax) const
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{
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// choose an x between Xmin and Xmax with P(x) ~ 1/x
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// to be improved...
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G4double range=Xmax-Xmin;
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if ( Xmin <= 0. || range <=0. )
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{
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G4cout << " Xmin, range : " << Xmin << " , " << range << G4endl;
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throw G4HadronicException(__FILE__, __LINE__, "G4SingleDiffractiveExcitation::ChooseX : Invalid arguments ");
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}
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G4double x;
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do {
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x=Xmin + G4UniformRand() * range;
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} while ( Xmin/x < G4UniformRand() ); /* Loop checking, 26.10.2015, A.Ribon */
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//cout << "DiffractiveX "<<x<<G4endl;
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return x;
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}
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G4ThreeVector G4SingleDiffractiveExcitation::GaussianPt(G4double widthSquare, G4double maxPtSquare) const
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{
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// @@ this method is used in FTFModel as well. Should go somewhere common!
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G4double pt2;
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const G4int maxNumberOfLoops = 1000;
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G4int loopCounter = -1;
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do {
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pt2=widthSquare * G4Log( G4UniformRand() );
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} while ( ( pt2 > maxPtSquare) && ++loopCounter < maxNumberOfLoops ); /* Loop checking, 26.10.2015, A.Ribon */
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if ( loopCounter >= maxNumberOfLoops ) pt2 = 0.0;
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pt2=std::sqrt(pt2);
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G4double phi=G4UniformRand() * twopi;
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return G4ThreeVector (pt2*std::cos(phi), pt2*std::sin(phi), 0.);
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}
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