Geant4 Hadronic |Physics Models

Geant4 Tutorial CERN, 25-27 May 2005 Gunter Folger Overview

„ Parton String Models – QGS Model „ Binary Cascade „ Precompound Model „ Nuclear de-excitation models „ CHIPS „ Capture Parton String Models

„ Quark Gluon String model „ Diffractive String Model

„ Models split into „ Strings excitation part „ String hadronization

„ Damaged nucleus passed to either „ pre-compound model (QGSP physics list) „ CHIPS for nuclear fragmentation (QGSC physics list) Quark Gluon String Model

„ Pomeron exchange model „ Hadrons exchange one or several Pomerons „ Equivalent to color coupling of valence quarks „ Partons connected by quark gluon strings Quark gluon string model Algorithm

„ A 3-dimensional nuclear model is built up „ Nucleus collapsed into 2 dimensions „ The impact parameter is calculated „ Hadron-nucleon collision probabilities calculation based on quasi-eikonal model, using Gaussian density distributions for hadrons and nucleons. „ Sampling of the number of Pomerons exchanged in each collision „ Unitarity cut, string formation and decay. QGSM - Results pi- Mg Æ pi+ X , Plab 320 GeV/c

1 ⎛ E + p ⎞ P 2 [GeV2] Rapidity η = ln⎜ z ⎟ t ⎜ − ⎟ 2 ⎝ E pz ⎠ Binary Cascade

„ Modeling interactions of protons, neutrons, pions with nuclei „ Incident particle kinetic energy 50 MeV – 2GeV „ Extension for light ion reactions

„ Wounded nucleus passed to pre-compound model and nuclear de-excitation models. Binary Cascade

„ Hybrid between classical cascade and full QMD model „ Detailed model of Nucleus „ nucleons placed in space according to nuclear density „ Nucleon momentum according to Fermi gas model „ Collective effect of nucleus on participant nucleons described by optical potential „ Numerically integrate equation of motion Binary Cascade

„ Interactions between primary (or secondary) with nucleon described as two body reactions „ E.g. pp -> ∆(1232) N*(2190)

„ Nucleon and delta resonances up to 2GeV included „ Resonances decay according to lifetime Binary Cascade - results

p Pb -> n X Pre-compound model

„ The pre-compound nucleus is viewed as consisting of two parts „ A system of excitons carrying the excitation energy and momentum „ A nucleus, undisturbed apart from the excitons „ The exciton system is defined by the numbers of excitons, holes, and charged exitons and their total energy and momentum Pre-compound Model

„ The system of excitons and the nucleus evolves through „ Collisions between excitons (∆n=0, -2) „ Collisions between excitons and nucleons (∆n=+2) „ Particle and fragment emission (up to helium) „ Until number of excitons is in equilibrium n = 2gU Nuclear de-excitation models

„ Nucleus is in equilibrium „ System is characterised by number of nucleons (A,Z) and excitation energy „ Excitation energy is distributed over large number of nucleons

„ De-excite nucleus through evaporation Nuclear de-excitation models

„ Weisskopf Ewing evaporation „ GEM evaporation „ Photon evaporation „ Internal conversion „ Fission „ Heavy nuclei (A≥65) „ Fermi break-up „ Light nuclei ( A<17) „ Multifragmentation „ Large excitation energy U/A > 3 MeV Chiral Invariant Phase Space (CHIPS)

„ CHIPS is based on homogeneous invariant phase distribution of mass-less partons „ Quasmon is ensemble of partons

„ Quasmon is characterised by mass MQ

„ Critical temperature TC defines number n of partons in Quasmon

„ TC is only parameter of model

„ MQ ≈ 2n TC „ Nucleus made of nucleon clusters Chiral Invariant Phase Space (CHIPS)

„ Critical temperature defines hadronic masses (EPJA- 14,265) „ Simulation of proton-antiproton annihilation at rest (EPJA-8,217) „ Quasmon creation in vacuum „ quark fusion hadronization mechanism for energy dissipation „ Pion capture and evaporation algorithm (EPJA-9,411) „ Quasmon creation in nuclear matter „ Quasmon can exchange quarks with nuclear clusters „ quark exchange hadronization mechanism „ Photonuclear reactions (EPJA-9, 421) „ Photonuclear absorption cross sections (EPJA-14,377) Chiral Invariant Phase Space (CHIPS)

„ Momentum of primary parton is k=(E-B*m+p)/2 „ B is a baryon number of the secondary hadron, „ E,p are energy and momentum of the secondary hadron „ m is mass of nuclear cluster „ measuring E and p of the hadron with known B, one can reconstruct spectra of primary partons. „ In simplified one dimentional case (q momentum of recoil parton): „ Baryons: k+M=E+q, k=p-q -> k=(E-M+p)/2 (quark exchange) „ Mesons: k+q=E, k-q=p -> k=(E+p)/2 (quark-antiquark fusion) „ Antibaryons: k+q=M+E, k-q=p: k=(E+M+p)/2 (antiquark-antidiquark fusion) „ In CHIPS the hadronization is made in three dimensions p+Ta=h+X, 400 GeV, 90o 2 2

10 10 p, mb/GeV p, mb/GeV 3 3

/d 1 /d 1 σ σ 3 3

-1 -1 10 10 (E/A)*d (E/A)*d

-2 -2 10 10

-3 -3 10 10

-4 -4 10 10

-5 -5 10 10 0 0.5 1 0.25 0.5 0.75 1 1.25

Ekin, GeV k=(E+p-B*M)/2, GeV Nuclear Capture of Negative Particles at Rest „ This simulation does not need any interaction cross- section „ Parameterised+theoretical models for π- and K- „ Absorption parameterised „ De-excitatin of nucleus nuclear de-excitation models „ Core code: CHIPS (Chiral Invariant Phase Space) model „ Valid for µ-,tau-, π-, K-, anti-proton, neutron, anti-neutron, sigma-, anti-sigma+, Xi-, Omega- „ For µ- and tau- mesons this is a hybrid model creating „ Photons and Auger electrons from intra-atomic cascade (electromagnetic process) „ neutrinos radiated when the meson interacts with the nuclear quark (weak process) „ hadrons and nuclear fragments, created from the recoil quark interacting with nuclear matter (hadronic process) Nuclear Capture of Negative Particles at Rest using CHIPS (continued) „ π- and K- mesons are captured by nuclear clusters with subsequent hadronization „ Anti-barions (anti-hyperons) annihilate on the surface of nuclei with quasifree nucleons „ secondary mesons interact with nuclear matter „ neutrons are included for heavy nuclei, which can absorb low energy neutrons and decay. Using Nuclear Capture of Negative Particles at Rest using CHIPS „ The G4QCaptureAtRest process can be used for all negative particles, for negative pions:

G4PionMinusInelasticProcess thePionMinusInelastic; G4LEPionMinusInelastic* theLEPionMinusModel; G4MultipleScattering thePionMinusMult; G4hIonisation thePionMinusIonisation; G4QCaptureAtRest thePionMinusAbsorption;

pManager = G4PionMinus::PionMinus()->GetProcessManager(); pManager->AddDiscreteProcess(&theElasticProcess); theLEPionMinusModel = new G4LEPionMinusInelastic(); thePionMinusInelastic.RegisterMe(theLEPionMinusModel); pManager->AddDiscreteProcess(&thePionMinusInelastic); pManager->AddProcess(&thePionMinusIonisation, ordInActive,2, 2); pManager->AddProcess(&thePionMinusMult); pManager->AddRestProcess(&thePionMinusAbsorption, ordDefault); Validation of CHIPS model for pion Capture at Rest on Carbon Pion capture on 12C nucleus -1 10 „-2 {use attachedneutrons picapC.eps file} deuterons 10 〈 〉 〈 〉 -3 Ekin e/m = 79.8 / 67.8 MeV Ekin e/m = 5.2 / 5.4 MeV 10 -4 10 -5

) 10 -6 -1 10 -7 10 -8 10 -9 protons Capture 10 〈E 〉 = 8.7 / 9.8 MeV -2 kin e/m -1 10 -2 10 tritium Helium-4 -3 〈E 〉 = 2.5 / 1.8 MeV 〈E 〉 = 5.3 / 5.9 MeV 10 kin e/m kin e/m -4 10 -5

dN/pdE (MeV 10 -6 10 -7 10 -8 10 -9 Helium-3 Lithium 〈 〉 10 Ekin e/m = 0.6 / 0.8 MeV 0 200 400 0 200 400

k = (p+Ekin)/2 (MeV) Validation of CHIPS for Anti-Proton Capture at Rest on Uranium Antiproton annihilation on 238U nucleus

-2 protons 10„ {use attached u92146_c.eps file}neutrons deuterons tritons (x 0.1) -3 kaons (x 100) 10 pions (x 100) ) He-3 (x 0.1) -1 He-4 (x 0.001) -4 10

-5 10 Annihilation -2 -6 10

-7 10

dN/pdE (MeV -8 10

-9 10

200 400 600 800 1000

k = (p+Ekin)/2 (MeV) Also…..

„ Inelastic Ion reactions „ Binary Cascade „ Abrasion/Ablation „ Electromagnetic dissociation „ Nuclear elastic „ Coherent elastic nucleon-nucleon scattering „ Muon nuclear „ Leading Particle Bias (partial MARS re-write) „ Radioactive decay „ Biasing Summary

„ Validation of physics list for specific use case important „ For new use cases absolutely needed

„ Further reading: „ Geant4 Physics reference manual „ Navigate from Geant4 home page http://cern.ch/geant4 „ Geant4 «Results&Publications» web page „ “Physics of shower simulation at LHC, at the example of Geant4”, J.P. Wellisch, CERN Academic training March 1-4, 2004. „ http://agenda.cern.ch/fullAgenda.php?ida=a036555