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[u/mrichter/AliRoot.git] / EVGEN / AliSlowNucleonModelExp.cxx

/**************************************************************************
 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
 *                                                                        *
 * Author: The ALICE Off-line Project.                                    *
 * Contributors are mentioned in the code where appropriate.              *
 *                                                                        *
 * Permission to use, copy, modify and distribute this software and its   *
 * documentation strictly for non-commercial purposes is hereby granted   *
 * without fee, provided that the above copyright notice appears in all   *
 * copies and that both the copyright notice and this permission notice   *
 * appear in the supporting documentation. The authors make no claims     *
 * about the suitability of this software for any purpose. It is          *
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/

/* $Id$ */

//
// Experimental data inspired Gray Particle Model for p-Pb collisions
// The number of gray nucleons  is proportional to the number of collisions.
// The number of black nucleons is proportional to the number of collisions
// Fluctuations are calculated from a binomial distribution.
// Author: A.Morsch
//

#include "AliSlowNucleonModelExp.h"
#include "AliCollisionGeometry.h"
#include <TRandom.h>
#include <TMath.h>

ClassImp(AliSlowNucleonModelExp)


AliSlowNucleonModelExp::AliSlowNucleonModelExp():
    fP(82),
    fN (126),
    fAlphaGray(2.3),
    fAlphaBlack(3.6),
    fApplySaturation(kTRUE),
    fnGraySaturation(15),
    fnBlackSaturation(28),
    fLCPparam(0.585)
{
  //
  // Default constructor
  //
  //
  fSlownparam[0] = 60.;
  fSlownparam[1] = 469.2;
  fSlownparam[2] = 8.762;
  printf("\n\n ******** Initializing slow nucleon model with parameters:\n");
  printf(" \t alpha_{gray} %1.2f  alpha_{black} %1.2f\n",fAlphaGray, fAlphaBlack);
  printf(" \t SATURATION %d w. %d (gray) %d (black) \n\n",fApplySaturation,fnGraySaturation,fnBlackSaturation);
  printf(" \t LCP parameter %f   Slown parameters = {%f, %f, %f}\n\n",fLCPparam,fSlownparam[0],fSlownparam[1],fSlownparam[2]); 
}


void AliSlowNucleonModelExp::GetNumberOfSlowNucleons(AliCollisionGeometry* geo, 
						      Int_t& ngp, Int_t& ngn, Int_t & nbp, Int_t & nbn) const
{
//
// Return the number of black and gray nucleons
//
// Number of collisions

    Float_t nu = geo->NN() + geo->NwN() + geo->NNw(); 

// Mean number of gray nucleons 

    Float_t nGray         = fAlphaGray * nu;
    Float_t nGrayNeutrons = nGray * fN / (fN + fP);
    Float_t nGrayProtons  = nGray - nGrayNeutrons;

// Mean number of black nucleons 
    Float_t nBlack  = 0.;
    if(!fApplySaturation || (fApplySaturation && nGray<fnGraySaturation)) nBlack = fAlphaBlack * nu;
    else if(fApplySaturation && nGray>=fnGraySaturation) nBlack = fnBlackSaturation;
    Float_t nBlackNeutrons = nBlack * 0.84;
    Float_t nBlackProtons  = nBlack - nBlackNeutrons;

// Actual number (including fluctuations) from binomial distribution
    Double_t p;

//  gray neutrons
    p =  nGrayNeutrons/fN;
    ngn = gRandom->Binomial((Int_t) fN, p);
    
//  gray protons
    p =  nGrayProtons/fP;
    ngp = gRandom->Binomial((Int_t) fP, p);

//  black neutrons
    p =  nBlackNeutrons/fN;
    nbn = gRandom->Binomial((Int_t) fN, p);
    
//  black protons
    p =  nBlackProtons/fP;
    nbp = gRandom->Binomial((Int_t) fP, p);

}

void AliSlowNucleonModelExp::GetNumberOfSlowNucleons2(AliCollisionGeometry* geo, 
						      Int_t& ngp, Int_t& ngn, Int_t & nbp, Int_t & nbn) const
{
//
// Return the number of black and gray nucleons
//
// Number of collisions

   // based on E910 model ================================================================

   Float_t nu = (Float_t) (geo->NN() + geo->NwN() + geo->NNw()); 
   //
   nu = nu+1.*gRandom->Rndm();
   //
   Float_t  poverpd = 0.843; 
   Float_t  zAu2zPb = 82./79.;
   Float_t  nGrayp = (-0.27 + 0.63 * nu - 0.0008 *nu *nu)*poverpd*zAu2zPb;

//  gray protons
    Double_t p;
    p =  nGrayp/fP;
    ngp = gRandom->Binomial((Int_t) fP, p);
    //ngp = gRandom->Gaus(nGrayp, TMath::Sqrt(fP*p*(1-p)));
    if(nGrayp<0.) ngp=0;
    
    //Float_t blackovergray = 3./7.;// from spallation
    Float_t blackovergray = 0.65; // from COSY
    Float_t nBlackp  = blackovergray*nGrayp; 

//  black protons
    p =  nBlackp/fP;
    nbp = gRandom->Binomial((Int_t) fP, p);
    //nbp = gRandom->Gaus(nBlackp, TMath::Sqrt(fP*p*(1-p)));
    if(nBlackp<0.) nbp=0;
    
    if(nu<3.){
      nGrayp = -0.836 + 0.9112 *nu - 0.05381 *nu *nu;
      nBlackp  = blackovergray*nGrayp; 
    }
    
    //printf(" \t Using LCP parameter %f   Slown parameters = {%f, %f, %f}\n\n",fLCPparam,fSlownparam[0],fSlownparam[1],fSlownparam[2]); 
    Float_t nGrayNeutrons = 0.;
    Float_t nBlackNeutrons = 0.;
    Float_t cp = (nGrayp+nBlackp)/fLCPparam;
    
    if(cp>0.){
      Float_t nSlow      = fSlownparam[0]+fSlownparam[1]/(-fSlownparam[2]-cp);
      Float_t paramRetta = fSlownparam[0]+fSlownparam[1]/(-fSlownparam[2]-3);
      if(cp<3.) nSlow = 0.+(paramRetta-0.)/(3.-0.)*(cp-0.);
    
      nGrayNeutrons = nSlow * 0.1; 
      nBlackNeutrons = nSlow - nGrayNeutrons;
    }
    else{
      // Sikler "pasturato" (qui non entra mai!!!!)
      nGrayNeutrons = 0.47 * fAlphaGray *  nu; 
      nBlackNeutrons = 0.88 * fAlphaBlack * nu;      
      printf("nslowp=0 -> ncoll = %1.0f -> ngrayn = %1.0f  nblackn = %1.0f \n", nu, nGrayNeutrons, nBlackNeutrons);
    }
    
//  gray neutrons
    p =  nGrayNeutrons/fN;
//    ngn = gRandom->Binomial((Int_t) fN, p);
    ngn = gRandom->Gaus(nGrayNeutrons, TMath::Sqrt(fN*p*(1-p)));

//  black neutrons
    p =  nBlackNeutrons/fN;
//    nbn = gRandom->Binomial((Int_t) fN, p);
    nbn = gRandom->Gaus(nBlackNeutrons, TMath::Sqrt(fN*p*(1-p)));
    
    
}

void AliSlowNucleonModelExp::SetParameters(Float_t alpha1, Float_t alpha2)
{
    // Set the model parameters
    fAlphaGray  = alpha1;
    fAlphaBlack = alpha2;
}