1 // BeamParticle.h is a part of the PYTHIA event generator.
2 // Copyright (C) 2012 Torbjorn Sjostrand.
3 // PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
4 // Please respect the MCnet Guidelines, see GUIDELINES for details.
6 // Header file for information on incoming beams.
7 // ResolvedParton: an initiator or remnant in beam.
8 // BeamParticle: contains partons, parton densities, etc.
10 #ifndef Pythia8_BeamParticle_H
11 #define Pythia8_BeamParticle_H
15 #include "FragmentationFlavZpT.h"
17 #include "ParticleData.h"
18 #include "PartonDistributions.h"
19 #include "PythiaStdlib.h"
24 //==========================================================================
26 // This class holds info on a parton resolved inside the incoming beam,
27 // i.e. either an initiator (part of a hard or a multiparton interaction)
28 // or a remnant (part of the beam remnant treatment).
30 // The companion code is -1 from onset and for g, is -2 for an unmatched
31 // sea quark, is >= 0 for a matched sea quark, with the number giving the
32 // companion position, and is -3 for a valence quark.
34 // Rescattering partons properly do not belong here, but bookkeeping is
35 // simpler with them, so they are stored with companion code -10.
37 class ResolvedParton {
42 ResolvedParton( int iPosIn = 0, int idIn = 0, double xIn = 0.,
43 int companionIn = -1) : iPosRes(iPosIn), idRes(idIn), xRes(xIn),
44 companionRes(companionIn), xqCompRes(0.), mRes(0.), factorRes(1.),
45 colRes(0), acolRes(0) { }
47 // Set info on initiator or remnant parton.
48 void iPos( int iPosIn) {iPosRes = iPosIn;}
49 void id( int idIn) {idRes = idIn;}
50 void x( double xIn) {xRes = xIn;}
51 void update( int iPosIn, int idIn, double xIn) {iPosRes = iPosIn;
52 idRes = idIn; xRes = xIn;}
53 void companion( int companionIn) {companionRes = companionIn;}
54 void xqCompanion( double xqCompIn) {xqCompRes = xqCompIn;}
55 void p(Vec4 pIn) {pRes = pIn;}
56 void px(double pxIn) {pRes.px(pxIn);}
57 void py(double pyIn) {pRes.py(pyIn);}
58 void pz(double pzIn) {pRes.pz(pzIn);}
59 void e(double eIn) {pRes.e(eIn);}
60 void m(double mIn) {mRes = mIn;}
61 void col(int colIn) {colRes = colIn;}
62 void acol(int acolIn) {acolRes = acolIn;}
63 void cols(int colIn = 0,int acolIn = 0)
64 {colRes = colIn; acolRes = acolIn;}
65 void scalePT( double factorIn) {pRes.px(factorIn * pRes.px());
66 pRes.py(factorIn * pRes.py()); factorRes *= factorIn;}
67 void scaleX( double factorIn) {xRes *= factorIn;}
69 // Get info on initiator or remnant parton.
70 int iPos() const {return iPosRes;}
71 int id() const {return idRes;}
72 double x() const {return xRes;}
73 int companion() const {return companionRes;}
74 bool isValence() const {return (companionRes == -3);}
75 bool isUnmatched() const {return (companionRes == -2);}
76 bool isCompanion() const {return (companionRes >= 0);}
77 bool isFromBeam() const {return (companionRes > -10);}
78 double xqCompanion() const {return xqCompRes;}
79 Vec4 p() const {return pRes;}
80 double px() const {return pRes.px();}
81 double py() const {return pRes.py();}
82 double pz() const {return pRes.pz();}
83 double e() const {return pRes.e();}
84 double m() const {return mRes;}
85 double pT() const {return pRes.pT();}
86 double mT2() const {return (mRes >= 0.)
87 ? mRes*mRes + pRes.pT2() : - mRes*mRes + pRes.pT2();}
88 double pPos() const {return pRes.e() + pRes.pz();}
89 double pNeg() const {return pRes.e() - pRes.pz();}
90 int col() const {return colRes;}
91 int acol() const {return acolRes;}
92 double pTfactor() const {return factorRes;}
96 // Properties of a resolved parton.
99 // Companion code and distribution value, if any.
102 // Four-momentum and mass; for remnant kinematics construction.
104 double mRes, factorRes;
110 //==========================================================================
112 // This class holds info on a beam particle in the evolution of
113 // initial-state radiation and multiparton interactions.
120 BeamParticle() : nInit(0) {resolved.resize(0); Q2ValFracSav = -1.;}
122 // Initialize data on a beam particle and save pointers.
123 void init( int idIn, double pzIn, double eIn, double mIn,
124 Info* infoPtrIn, Settings& settings, ParticleData* particleDataPtrIn,
125 Rndm* rndmPtrIn, PDF* pdfInPtr, PDF* pdfHardInPtr, bool isUnresolvedIn,
126 StringFlav* flavSelPtrIn);
128 // For mesons like pi0 valence content varies from event to event.
129 void newValenceContent();
131 // Set new pZ and E, but keep the rest the same.
132 void newPzE( double pzIn, double eIn) {pBeam = Vec4( 0., 0., pzIn, eIn);}
134 // Member functions for output.
135 int id() const {return idBeam;}
136 Vec4 p() const {return pBeam;}
137 double px() const {return pBeam.px();}
138 double py() const {return pBeam.py();}
139 double pz() const {return pBeam.pz();}
140 double e() const {return pBeam.e();}
141 double m() const {return mBeam;}
142 bool isLepton() const {return isLeptonBeam;}
143 bool isUnresolved() const {return isUnresolvedBeam;}
144 // As hadrons here we only count those we know how to handle remnants for.
145 bool isHadron() const {return isHadronBeam;}
146 bool isMeson() const {return isMesonBeam;}
147 bool isBaryon() const {return isBaryonBeam;}
149 // Maximum x remaining after previous MPI and ISR, plus safety margin.
150 double xMax(int iSkip = -1);
152 // Special hard-process parton distributions (can agree with standard ones).
153 double xfHard(int idIn, double x, double Q2)
154 {return pdfHardBeamPtr->xf(idIn, x, Q2);}
156 // Standard parton distributions.
157 double xf(int idIn, double x, double Q2)
158 {return pdfBeamPtr->xf(idIn, x, Q2);}
160 // Ditto, split into valence and sea parts (where gluon counts as sea).
161 double xfVal(int idIn, double x, double Q2)
162 {return pdfBeamPtr->xfVal(idIn, x, Q2);}
163 double xfSea(int idIn, double x, double Q2)
164 {return pdfBeamPtr->xfSea(idIn, x, Q2);}
166 // Rescaled parton distributions, as needed for MPI and ISR.
167 // For ISR also allow split valence/sea, and only return relevant part.
168 double xfMPI(int idIn, double x, double Q2)
169 {return xfModified(-1, idIn, x, Q2);}
170 double xfISR(int indexMPI, int idIn, double x, double Q2)
171 {return xfModified( indexMPI, idIn, x, Q2);}
173 // Decide whether chosen quark is valence, sea or companion.
174 int pickValSeaComp();
176 // Initialize kind of incoming beam particle.
179 // Overload index operator to access a resolved parton from the list.
180 ResolvedParton& operator[](int i) {return resolved[i];}
182 // Total number of partons extracted from beam, and initiators only.
183 int size() const {return resolved.size();}
184 int sizeInit() const {return nInit;}
186 // Clear list of resolved partons.
187 void clear() {resolved.resize(0); nInit = 0;}
189 // Add a resolved parton to list.
190 int append( int iPos, int idIn, double x, int companion = -1)
191 {resolved.push_back( ResolvedParton( iPos, idIn, x, companion) );
192 return resolved.size() - 1;}
194 // Print extracted parton list; for debug mainly.
195 void list(ostream& os = cout) const;
197 // How many different flavours, and how many quarks of given flavour.
198 int nValenceKinds() const {return nValKinds;}
199 int nValence(int idIn) const {for (int i = 0; i < nValKinds; ++i)
200 if (idIn == idVal[i]) return nVal[i]; return 0;}
202 // Test whether a lepton is to be considered as unresolved.
203 bool isUnresolvedLepton();
205 // Add extra remnant flavours to make valence and sea come out right.
206 bool remnantFlavours(Event& event);
208 // Correlate all initiators and remnants to make a colour singlet.
209 bool remnantColours(Event& event, vector<int>& colFrom,
212 // Pick unrescaled x of remnant parton (valence or sea).
213 double xRemnant(int i);
215 // Tell whether a junction has been resolved, and its junction colours.
216 bool hasJunction() const {return hasJunctionBeam;}
217 int junctionCol(int i) const {return junCol[i];}
218 void junctionCol(int i, int col) {junCol[i] = col;}
220 // For a diffractive system, decide whether to kick out gluon or quark.
221 bool pickGluon(double mDiff);
223 // Pick a valence quark at random, and provide the remaining flavour.
225 int pickRemnant() const {return idVal2;}
227 // Share lightcone momentum between two remnants in a diffractive system.
228 // At the same time generate a relative pT for the two.
229 double zShare( double mDiff, double m1, double m2);
230 double pxShare() const {return pxRel;}
231 double pyShare() const {return pyRel;}
235 // Constants: could only be changed in the code itself.
236 static const double XMINUNRESOLVED;
238 // Pointer to various information on the generation.
241 // Pointer to the particle data table.
242 ParticleData* particleDataPtr;
244 // Pointer to the random number generator.
247 // Pointers to PDF sets.
251 // Pointer to class for flavour generation.
252 StringFlav* flavSelPtr;
254 // Initialization data, normally only set once.
256 int maxValQuark, companionPower;
257 double valencePowerMeson, valencePowerUinP, valencePowerDinP,
258 valenceDiqEnhance, pickQuarkNorm, pickQuarkPower,
259 diffPrimKTwidth, diffLargeMassSuppress;
261 // Basic properties of a beam particle.
262 int idBeam, idBeamAbs;
265 // Beam kind. Valence flavour content for hadrons.
266 bool isUnresolvedBeam, isLeptonBeam, isHadronBeam, isMesonBeam,
268 int nValKinds, idVal[3], nVal[3];
270 // Current parton density, by valence, sea and companion.
271 int idSave, iSkipSave, nValLeft[3];
272 double xqgTot, xqVal, xqgSea, xqCompSum;
274 // The list of resolved partons.
275 vector<ResolvedParton> resolved;
277 // Status after all initiators have been accounted for. Junction content.
279 bool hasJunctionBeam;
282 // Routine to calculate pdf's given previous interactions.
283 double xfModified( int iSkip, int idIn, double x, double Q2);
285 // Fraction of hadron momentum sitting in a valence quark distribution.
286 double xValFrac(int j, double Q2);
287 double Q2ValFracSav, uValInt, dValInt;
289 // Fraction of hadron momentum sitting in a companion quark distribution.
290 double xCompFrac(double xs);
292 // Value of companion quark PDF, also given the sea quark x.
293 double xCompDist(double xc, double xs);
295 // Valence quark subdivision for diffractive systems.
296 int idVal1, idVal2, idVal3;
297 double zRel, pxRel, pyRel;
301 //==========================================================================
303 } // end namespace Pythia8
305 #endif // Pythia8_BeamParticle_H