[u/mrichter/AliRoot.git] / EVGEN / AliGenSlowNucleons.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.                  *
 **************************************************************************/

/* $Id$ */

//
//  Generator for slow nucleons in pA interactions. 
//  Source is modelled by a relativistic Maxwell distributions.
//  This class cooparates with AliCollisionGeometry if used inside AliGenCocktail.
//  In this case the number of slow nucleons is determined from the number of wounded nuclei
//  using a realisation of AliSlowNucleonModel.
//  Original code by  Ferenc Sikler  <sikler@rmki.kfki.hu>
// 

#include <TDatabasePDG.h>
#include <TPDGCode.h>
#include <TH2F.h>
#include <TH1F.h>
#include <TF1.h>
#include <TCanvas.h>

#include "AliCollisionGeometry.h"
#include "AliGenSlowNucleons.h"
#include "AliSlowNucleonModel.h"

ClassImp(AliGenSlowNucleons)

    
AliGenSlowNucleons::AliGenSlowNucleons()
    :AliGenerator(-1),
     fCMS(0.),
     fMomentum(0.),
     fBeta(0.),
     fPmax (0.),
     fCharge(0),
     fProtonDirection(1.),
     fTemperatureG(0.), 
     fBetaSourceG(0.),
     fTemperatureB(0.),
     fBetaSourceB(0.),
     fNgp(0),
     fNgn(0),
     fNbp(0),
     fNbn(0),
     fDebug(0),
     fDebugHist1(0),
     fDebugHist2(0),
     fThetaDistribution(),
     fCosThetaGrayHist(),
     fCosTheta(),
     fSlowNucleonModel(0)
{
// Default constructor
    fCollisionGeometry = 0;
}

AliGenSlowNucleons::AliGenSlowNucleons(Int_t npart)
    :AliGenerator(npart),
     fCMS(14000.),
     fMomentum(0.),
     fBeta(0.),
     fPmax (10.),
     fCharge(1),
     fProtonDirection(1.),
     fTemperatureG(0.05), 
     fBetaSourceG(0.05),
     fTemperatureB(0.005),
     fBetaSourceB(0.),
     fNgp(0),
     fNgn(0),
     fNbp(0),
     fNbn(0),
     fDebug(0),
     fDebugHist1(0),
     fDebugHist2(0),
     fThetaDistribution(),
     fCosThetaGrayHist(),
     fCosTheta(),
     fSlowNucleonModel(new AliSlowNucleonModel())
{
// Constructor
    fName  = "SlowNucleons";
    fTitle = "Generator for gray particles in pA collisions";
    fCollisionGeometry = 0;
}

//____________________________________________________________
AliGenSlowNucleons::~AliGenSlowNucleons()
{
// Destructor
    delete  fSlowNucleonModel;
}

void AliGenSlowNucleons::SetProtonDirection(Float_t dir) {
// Set direction of the proton to change between pA (1) and Ap (-1)
  fProtonDirection = dir / TMath::Abs(dir);
}

void AliGenSlowNucleons::Init()
{
  //
  // Initialization
  //
    Float_t kMass  = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
    fMomentum = fCMS/2. * Float_t(fZTarget) / Float_t(fATarget);
    fBeta     = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
    if (fDebug) {
	fDebugHist1 = new TH2F("DebugHist1", "nu vs N_slow", 100, 0., 100., 20, 0., 20.);
	fDebugHist2 = new TH2F("DebugHist2", "b  vs N_slow", 100, 0., 100., 15, 0., 15.);
    	fCosThetaGrayHist = new TH1F("fCosThetaGrayHist", "Gray particles angle", 100, -1., 1.);
    }
    //
    // non-uniform cos(theta) distribution
    //
    if(fThetaDistribution != 0) {
	fCosTheta = new TF1("fCosTheta",
			    "(2./3.14159265358979312)/(exp(2./3.14159265358979312)-exp(-2./3.14159265358979312))*exp(2.*x/3.14159265358979312)",
			    -1., 1.);
    }
}

void AliGenSlowNucleons::FinishRun()
{
// End of run action
// Show histogram for debugging if requested.
    if (fDebug) {
	TCanvas *c = new TCanvas("c","Canvas 1",400,10,600,700);
	c->Divide(2,1);
	c->cd(1);
	fDebugHist1->Draw();
	c->cd(2);
	fDebugHist2->Draw();
	c->cd(3);
	fCosThetaGrayHist->Draw();
    }
}


void AliGenSlowNucleons::Generate()
{
  //
  // Generate one event
  //
  //
  // Communication with Gray Particle Model 
  // 
    if (fCollisionGeometry) {
	Float_t b   = fCollisionGeometry->ImpactParameter();
	//	Int_t  nn   = fCollisionGeometry->NN();
	//      Int_t  nwn  = fCollisionGeometry->NwN();
	//      Int_t  nnw  = fCollisionGeometry->NNw();
	//      Int_t  nwnw = fCollisionGeometry->NwNw();

	fSlowNucleonModel->GetNumberOfSlowNucleons(fCollisionGeometry, fNgp, fNgn, fNbp, fNbn);
	if (fDebug) {
	    printf("Slow nucleons: %d grayp  %d grayn  %d blackp  %d blackn \n", fNgp, fNgn, fNbp, fNbn);
	    fDebugHist1->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), fCollisionGeometry->NwN(), 1.);
	    fDebugHist2->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), b, 1.);
	    //printf("AliGenSlowNucleons: Impact parameter from Collision Geometry %f %d %d %d %d\n", b, nn, nwn, nnw, nwnw);
	}
    }     

   //
    Float_t p[3], theta=0;
    Float_t origin[3] = {0., 0., 0.};
    Float_t time = 0.;
    Float_t polar [3] = {0., 0., 0.};    
    Int_t nt, i, j;
    Int_t kf;
    
    if(fVertexSmear == kPerEvent) {
	Vertex();
	for (j=0; j < 3; j++) origin[j] = fVertex[j];
	time = fTime;
    } // if kPerEvent
//
//  Gray protons
//
    fCharge = 1;
    kf = kProton;    
    for(i = 0; i < fNgp; i++) {
	GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p, theta);
	if (fDebug) fCosThetaGrayHist->Fill(TMath::Cos(theta));
	PushTrack(fTrackIt, -1, kf, p, origin, polar,
		 time, kPNoProcess, nt, 1.);
	KeepTrack(nt);
    }
//
//  Gray neutrons
//
    fCharge = 0;
    kf = kNeutron;    
    for(i = 0; i < fNgn; i++) {
	GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p, theta);
	if (fDebug) fCosThetaGrayHist->Fill(TMath::Cos(theta));
	PushTrack(fTrackIt, -1, kf, p, origin, polar,
		 time, kPNoProcess, nt, 1.);
	KeepTrack(nt);
    }
//
//  Black protons
//
    fCharge = 1;
    kf = kProton;    
    for(i = 0; i < fNbp; i++) {
	GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p, theta);
	PushTrack(fTrackIt, -1, kf, p, origin, polar,
		 time, kPNoProcess, nt, 1.);
	KeepTrack(nt);
    }
//
//  Black neutrons
//
    fCharge = 0;
    kf = kNeutron;    
    for(i = 0; i < fNbn; i++) {
	GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p, theta);
	PushTrack(fTrackIt, -1, kf, p, origin, polar,
		 time, kPNoProcess, nt, 1.);
	KeepTrack(nt);
    }
}


void AliGenSlowNucleons::GenerateSlow(Int_t charge, Double_t T, 
	Double_t beta, Float_t* q, Float_t &theta)

{
/* 
   Emit a slow nucleon with "temperature" T [GeV], 
   from a source moving with velocity beta         
   Three-momentum [GeV/c] is given back in q[3]    
*/

 //printf("Generating slow nuc. with: charge %d. temp. %1.3f, beta %1.2f\n",charge,T,beta);
 
 Double_t m, pmax, p, f, phi;
 TDatabasePDG * pdg = TDatabasePDG::Instance();
 const Double_t kMassProton  = pdg->GetParticle(kProton) ->Mass();
 const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
 
 /* Select nucleon type */
 if(charge == 0) m = kMassNeutron;
 else m = kMassProton;

 /* Momentum at maximum of Maxwell-distribution */

 pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m)));

 /* Try until proper momentum                                  */
 /* for lack of primitive function of the Maxwell-distribution */
 /* a brute force trial-accept loop, normalized at pmax        */

 do
 {
     p = Rndm() * fPmax;
     f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
 }
 while(f < Rndm());

 /* Spherical symmetric emission for black particles (beta=0)*/
 if(beta==0 || fThetaDistribution==0) theta = TMath::ACos(2. * Rndm() - 1.);
 /* cos theta distributed according to experimental results for gray particles (beta=0.05)*/
 else if(fThetaDistribution!=0){
   Double_t costheta = fCosTheta->GetRandom();
   theta = TMath::ACos(costheta);
 }
 //
 phi   = 2. * TMath::Pi() * Rndm();

 /* Determine momentum components in system of the moving source */
 q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
 q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
 q[2] = p * TMath::Cos(theta);

 /* Transform to system of the target nucleus                             */
 /* beta is passed as negative, because the gray nucleons are slowed down */
 Lorentz(m, -beta, q);

 /* Transform to laboratory system */
 Lorentz(m, fBeta, q);
 q[2] *= fProtonDirection; 
}

Double_t AliGenSlowNucleons::Maxwell(Double_t m, Double_t p, Double_t T)
{
/* Relativistic Maxwell-distribution */
    Double_t ekin;
    ekin = TMath::Sqrt(p*p+m*m)-m;
    return (p*p * exp(-ekin/T));
}


void AliGenSlowNucleons::Lorentz(Double_t m, Double_t beta, Float_t* q)
{
/* Lorentz transform in the direction of q[2] */
 
    Double_t gamma  = 1./sqrt((1.-beta)*(1.+beta)); 
    Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]);
    q[2] = gamma * (q[2] + beta*energy);
}
Commit	Line	Data
c9a8628a	1	/**************************************************************************
	2	* Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
	3	* *
	4	* Author: The ALICE Off-line Project. *
	5	* Contributors are mentioned in the code where appropriate. *
	6	* *
	7	* Permission to use, copy, modify and distribute this software and its *
	8	* documentation strictly for non-commercial purposes is hereby granted *
	9	* without fee, provided that the above copyright notice appears in all *
	10	* copies and that both the copyright notice and this permission notice *
	11	* appear in the supporting documentation. The authors make no claims *
	12	* about the suitability of this software for any purpose. It is *
	13	* provided "as is" without express or implied warranty. *
	14	**************************************************************************/
	15
88cb7938	16	/* $Id$ */
c9a8628a	17
f687abfe	18	//
	19	// Generator for slow nucleons in pA interactions.
	20	// Source is modelled by a relativistic Maxwell distributions.
	21	// This class cooparates with AliCollisionGeometry if used inside AliGenCocktail.
	22	// In this case the number of slow nucleons is determined from the number of wounded nuclei
	23	// using a realisation of AliSlowNucleonModel.
	24	// Original code by Ferenc Sikler <sikler@rmki.kfki.hu>
	25	//
c9a8628a	26
	27	#include <TDatabasePDG.h>
	28	#include <TPDGCode.h>
	29	#include <TH2F.h>
5a9b7f8e	30	#include <TH1F.h>
5a9b7f8e	31	#include <TF1.h>
c8f7f6f9	32	#include <TCanvas.h>
c9a8628a	33
	34	#include "AliCollisionGeometry.h"
	35	#include "AliGenSlowNucleons.h"
	36	#include "AliSlowNucleonModel.h"
	37
706938e6	38	ClassImp(AliGenSlowNucleons)
1c56e311	39
c9a8628a	40
1c56e311	41	AliGenSlowNucleons::AliGenSlowNucleons()
	42	:AliGenerator(-1),
	43	fCMS(0.),
	44	fMomentum(0.),
	45	fBeta(0.),
	46	fPmax (0.),
1c56e311	47	fCharge(0),
61cf877f	48	fProtonDirection(1.),
1c56e311	49	fTemperatureG(0.),
	50	fBetaSourceG(0.),
	51	fTemperatureB(0.),
	52	fBetaSourceB(0.),
	53	fNgp(0),
	54	fNgn(0),
	55	fNbp(0),
	56	fNbn(0),
	57	fDebug(0),
	58	fDebugHist1(0),
	59	fDebugHist2(0),
	60	fThetaDistribution(),
	61	fCosThetaGrayHist(),
	62	fCosTheta(),
	63	fSlowNucleonModel(0)
c9a8628a	64	{
c9a8628a	65	// Default constructor
c9a8628a	66	fCollisionGeometry = 0;
	67	}
	68
	69	AliGenSlowNucleons::AliGenSlowNucleons(Int_t npart)
1c56e311	70	:AliGenerator(npart),
	71	fCMS(14000.),
	72	fMomentum(0.),
	73	fBeta(0.),
	74	fPmax (10.),
1c56e311	75	fCharge(1),
61cf877f	76	fProtonDirection(1.),
230d85c6	77	fTemperatureG(0.05),
1c56e311	78	fBetaSourceG(0.05),
230d85c6	79	fTemperatureB(0.005),
1c56e311	80	fBetaSourceB(0.),
	81	fNgp(0),
	82	fNgn(0),
	83	fNbp(0),
	84	fNbn(0),
	85	fDebug(0),
	86	fDebugHist1(0),
	87	fDebugHist2(0),
	88	fThetaDistribution(),
	89	fCosThetaGrayHist(),
	90	fCosTheta(),
	91	fSlowNucleonModel(new AliSlowNucleonModel())
c9a8628a	92	{
	93	// Constructor
	94	fName = "SlowNucleons";
	95	fTitle = "Generator for gray particles in pA collisions";
c9a8628a	96	fCollisionGeometry = 0;
c9a8628a	97	}
	98
	99	//____________________________________________________________
	100	AliGenSlowNucleons::~AliGenSlowNucleons()
	101	{
	102	// Destructor
	103	delete fSlowNucleonModel;
	104	}
	105
83b3cd6c	106	void AliGenSlowNucleons::SetProtonDirection(Float_t dir) {
	107	// Set direction of the proton to change between pA (1) and Ap (-1)
	108	fProtonDirection = dir / TMath::Abs(dir);
	109	}
c9a8628a	110
	111	void AliGenSlowNucleons::Init()
	112	{
	113	//
	114	// Initialization
	115	//
	116	Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
271e6aae	117	fMomentum = fCMS/2. * Float_t(fZTarget) / Float_t(fATarget);
c9a8628a	118	fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
c9a8628a	119	if (fDebug) {
c8f7f6f9	120	fDebugHist1 = new TH2F("DebugHist1", "nu vs N_slow", 100, 0., 100., 20, 0., 20.);
c8f7f6f9	121	fDebugHist2 = new TH2F("DebugHist2", "b vs N_slow", 100, 0., 100., 15, 0., 15.);
5a9b7f8e	122	fCosThetaGrayHist = new TH1F("fCosThetaGrayHist", "Gray particles angle", 100, -1., 1.);
	123	}
	124	//
	125	// non-uniform cos(theta) distribution
	126	//
	127	if(fThetaDistribution != 0) {
	128	fCosTheta = new TF1("fCosTheta",
	129	"(2./3.14159265358979312)/(exp(2./3.14159265358979312)-exp(-2./3.14159265358979312))exp(2.x/3.14159265358979312)",
	130	-1., 1.);
c9a8628a	131	}
	132	}
	133
	134	void AliGenSlowNucleons::FinishRun()
	135	{
f687abfe	136	// End of run action
f687abfe	137	// Show histogram for debugging if requested.
c9a8628a	138	if (fDebug) {
c8f7f6f9	139	TCanvas *c = new TCanvas("c","Canvas 1",400,10,600,700);
	140	c->Divide(2,1);
	141	c->cd(1);
	142	fDebugHist1->Draw();
	143	c->cd(2);
	144	fDebugHist2->Draw();
5a9b7f8e	145	c->cd(3);
5a9b7f8e	146	fCosThetaGrayHist->Draw();
c9a8628a	147	}
	148	}
	149
	150
	151	void AliGenSlowNucleons::Generate()
	152	{
	153	//
	154	// Generate one event
	155	//
	156	//
	157	// Communication with Gray Particle Model
	158	//
1c22a81e	159	if (fCollisionGeometry) {
1c22a81e	160	Float_t b = fCollisionGeometry->ImpactParameter();
230d85c6	161	// Int_t nn = fCollisionGeometry->NN();
	162	// Int_t nwn = fCollisionGeometry->NwN();
	163	// Int_t nnw = fCollisionGeometry->NNw();
	164	// Int_t nwnw = fCollisionGeometry->NwNw();
1c22a81e	165
99f5114f	166	fSlowNucleonModel->GetNumberOfSlowNucleons(fCollisionGeometry, fNgp, fNgn, fNbp, fNbn);
1c22a81e	167	if (fDebug) {
230d85c6	168	printf("Slow nucleons: %d grayp %d grayn %d blackp %d blackn \n", fNgp, fNgn, fNbp, fNbn);
c8f7f6f9	169	fDebugHist1->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), fCollisionGeometry->NwN(), 1.);
c8f7f6f9	170	fDebugHist2->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), b, 1.);
230d85c6	171	//printf("AliGenSlowNucleons: Impact parameter from Collision Geometry %f %d %d %d %d\n", b, nn, nwn, nnw, nwnw);
1c22a81e	172	}
1c22a81e	173	}
c9a8628a	174
c9a8628a	175	//
5a9b7f8e	176	Float_t p[3], theta=0;
c9a8628a	177	Float_t origin[3] = {0., 0., 0.};
21391258	178	Float_t time = 0.;
c9a8628a	179	Float_t polar [3] = {0., 0., 0.};
99f5114f	180	Int_t nt, i, j;
c9a8628a	181	Int_t kf;
99f5114f	182
	183	if(fVertexSmear == kPerEvent) {
	184	Vertex();
	185	for (j=0; j < 3; j++) origin[j] = fVertex[j];
21391258	186	time = fTime;
99f5114f	187	} // if kPerEvent
c9a8628a	188	//
	189	// Gray protons
	190	//
	191	fCharge = 1;
	192	kf = kProton;
1c22a81e	193	for(i = 0; i < fNgp; i++) {
5a9b7f8e	194	GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p, theta);
5a9b7f8e	195	if (fDebug) fCosThetaGrayHist->Fill(TMath::Cos(theta));
642f15cf	196	PushTrack(fTrackIt, -1, kf, p, origin, polar,
21391258	197	time, kPNoProcess, nt, 1.);
c9a8628a	198	KeepTrack(nt);
	199	}
	200	//
	201	// Gray neutrons
	202	//
	203	fCharge = 0;
	204	kf = kNeutron;
1c22a81e	205	for(i = 0; i < fNgn; i++) {
5a9b7f8e	206	GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p, theta);
5a9b7f8e	207	if (fDebug) fCosThetaGrayHist->Fill(TMath::Cos(theta));
642f15cf	208	PushTrack(fTrackIt, -1, kf, p, origin, polar,
21391258	209	time, kPNoProcess, nt, 1.);
c9a8628a	210	KeepTrack(nt);
	211	}
	212	//
	213	// Black protons
	214	//
	215	fCharge = 1;
	216	kf = kProton;
1c22a81e	217	for(i = 0; i < fNbp; i++) {
5a9b7f8e	218	GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p, theta);
642f15cf	219	PushTrack(fTrackIt, -1, kf, p, origin, polar,
21391258	220	time, kPNoProcess, nt, 1.);
c9a8628a	221	KeepTrack(nt);
	222	}
	223	//
	224	// Black neutrons
	225	//
	226	fCharge = 0;
	227	kf = kNeutron;
1c22a81e	228	for(i = 0; i < fNbn; i++) {
5a9b7f8e	229	GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p, theta);
642f15cf	230	PushTrack(fTrackIt, -1, kf, p, origin, polar,
21391258	231	time, kPNoProcess, nt, 1.);
c9a8628a	232	KeepTrack(nt);
	233	}
	234	}
	235
	236
	237
	238
5a9b7f8e	239	void AliGenSlowNucleons::GenerateSlow(Int_t charge, Double_t T,
5a9b7f8e	240	Double_t beta, Float_t* q, Float_t &theta)
f687abfe	241
f687abfe	242	{
c9a8628a	243	/*
	244	Emit a slow nucleon with "temperature" T [GeV],
	245	from a source moving with velocity beta
	246	Three-momentum [GeV/c] is given back in q[3]
	247	*/
	248
230d85c6	249	//printf("Generating slow nuc. with: charge %d. temp. %1.3f, beta %1.2f\n",charge,T,beta);
230d85c6	250
5a9b7f8e	251	Double_t m, pmax, p, f, phi;
c9a8628a	252	TDatabasePDG * pdg = TDatabasePDG::Instance();
	253	const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass();
	254	const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
	255
	256	/* Select nucleon type */
	257	if(charge == 0) m = kMassNeutron;
	258	else m = kMassProton;
	259
	260	/* Momentum at maximum of Maxwell-distribution */
	261
	262	pmax = TMath::Sqrt(2T(T+sqrt(TT+mm)));
	263
	264	/* Try until proper momentum */
	265	/* for lack of primitive function of the Maxwell-distribution */
	266	/* a brute force trial-accept loop, normalized at pmax */
	267
	268	do
	269	{
	270	p = Rndm() * fPmax;
	271	f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
	272	}
	273	while(f < Rndm());
	274
5a9b7f8e	275	/* Spherical symmetric emission for black particles (beta=0)*/
	276	if(beta==0 \|\| fThetaDistribution==0) theta = TMath::ACos(2. * Rndm() - 1.);
	277	/* cos theta distributed according to experimental results for gray particles (beta=0.05)*/
	278	else if(fThetaDistribution!=0){
	279	Double_t costheta = fCosTheta->GetRandom();
	280	theta = TMath::ACos(costheta);
	281	}
	282	//
c9a8628a	283	phi = 2. * TMath::Pi() * Rndm();
	284
	285	/* Determine momentum components in system of the moving source */
	286	q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
	287	q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
	288	q[2] = p * TMath::Cos(theta);
	289
	290	/* Transform to system of the target nucleus */
	291	/* beta is passed as negative, because the gray nucleons are slowed down */
	292	Lorentz(m, -beta, q);
	293
	294	/* Transform to laboratory system */
	295	Lorentz(m, fBeta, q);
83b3cd6c	296	q[2] *= fProtonDirection;
c9a8628a	297	}
	298
	299	Double_t AliGenSlowNucleons::Maxwell(Double_t m, Double_t p, Double_t T)
	300	{
	301	/* Relativistic Maxwell-distribution */
	302	Double_t ekin;
	303	ekin = TMath::Sqrt(pp+mm)-m;
	304	return (pp exp(-ekin/T));
	305	}
	306
	307
	308	void AliGenSlowNucleons::Lorentz(Double_t m, Double_t beta, Float_t* q)
	309	{
	310	/* Lorentz transform in the direction of q[2] */
	311
61cf877f	312	Double_t gamma = 1./sqrt((1.-beta)*(1.+beta));
c9a8628a	313	Double_t energy = sqrt(mm + q[0]q[0] + q[1]q[1] + q[2]q[2]);
	314	q[2] = gamma * (q[2] + beta*energy);
	315	}
230d85c6	316