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Assessing Hadronic Shower Parameterizations in GEANT4: Insights and Challenges

This study evaluates the hadronic shower parameterizations implemented in GEANT4, specifically those based on the GHEISHA package. It addresses known issues encountered in GHEISHA and the subsequent implications for energy conservation and particle interactions. By analyzing basic interactions and shower behaviors, and improving energy calculations for hadronic interactions, we aim to enhance the reliability of simulation results. The findings highlight required corrections, potential bugs, and performance discrepancies compared to GEANT3, ultimately advancing our understanding of hadronic processes.

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Assessing Hadronic Shower Parameterizations in GEANT4: Insights and Challenges

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  1. Checking Basic Characteristics of Hadronic Shower Parameterizations in GHEISHA / GEANT4 • David Bailey • University of Toronto • dbailey@physics.utoronto.ca • Geant4 hadronic parameterization based on GHEISHA • GHEISHA known to have problems e.g. See A. Ferrari & P. Sala, ATLAS Note PHYS-96-086 • I couldn’t write such a large subpackage without initial bugs. • Before introducing real geometry, check: • Do basic interactions and showers look sensible? Hadronic Interactions

  2. Basic Parameters • GEANT 4.2.0 ref 2 • PhysicsList based on Example N04 • conserveEnergy = true • GEANT 3.21 • Particles generated at centre of huge uniform cubes • side half-length = 105 km • 1cm step cut • some G4 tracks cut at 1MeV • “Total Energy” is the sum of • step energy losses • cut track energies • neutrino energies (improved since last G4 meeting) Hadronic Interactions

  3. Total Energy for 100 GeV/c2+ in Tungsten Hadronic Interactions

  4. Total Energy for 100 GeV/c2+ in Liquid Deuterium Hadronic Interactions

  5. Total Energy for 1 GeV/c2 hadrons in Hydrogen Hadronic Interactions

  6. GEANT3 GHEISHA • Calculates the target mass in 2 places by counting the             outgoing particles with masses > 0.5 GeV. i.e. If the incoming particle is a baryon, the target is set 1 nucleon mass heavier than it is. • Can be fixed by 1 line of code, inserted twice. • SUBROUTINE TWOCLU(IPPP,NFL,AVERN) / SUBROUTINE GENXPT(IPPP,NFL,AVERN) • C *** GENERATION OF X- AND PT- VALUES FOR ALL PRODUCED PARTICLES *** • … • C** LORENTZ TRANSFORMATION IN LAB SYSTEM • C** • 27 TARG=0. • DO 36 I=1,NT • IF(PV(5,I).GT.0.5) TARG=TARG+1. • CALL LOR(I,MX2,I) • 36 CONTINUE • C*DCB --> David Baileymodification to prevent counting • C*DCB incoming baryon as a target particle • if (amas.gt.0.5) targ=targ-1. Hadronic Interactions

  7. GEANT4 Hadronic Package • Also calculates the target mass by counting outgoing “baryons” • in 1 place checking if mass > 0.5 GeV • Will increase target mass for charm or beauty production. • in 1 place checking if proton or neutron • Will decrease target mass if hyperon produced. • in 4 places by checking if baryon or antibaryon. • Double increase for antibaryon production, even for incident meson. • Corrections require 20 lines of code. • Not impossible that corrections may cause problems elsewhere. For example, there may be some reason for using different methods. • Needs further checking along with solutions to other bugs. Hadronic Interactions

  8. Antinucleons produce too much energy • In both GEANT4 and GHEISHA GEANT3. • Annihilation at rest is okay. • Total Energy for 1 GeV/c2 antineutrons in hydrogen Hadronic Interactions

  9. Kinetic energy modifications • Kinetic energy of antibaryons is increased for input for nuclear evaporation, and not set back. e.g. GEANT3/GHEISHA • SUBROUTINE CORANH(NIHIL,NFL) • … • C** DO NOT BE CONFUSED, THIS HAS NOTHING TO DO WITH RELATIVISTIC KINEMATICS • … • EKCOR=1. • IF(EK.GT.1.) EKCOR=1./EK • EK = 2.*TARMAS + EK*(1.+EKCOR/ATNO2) • … once in GEANT3, 3 times (2 versions) in GEANT4 Hadronic Interactions

  10. Two body scattering not always uniform • void G4ReactionKinematics::TwoBodyScattering( • … • // isotropic decay angle theta • G4double theta=RandFlat::shoot(HepDouble(0.),HepDouble(pi)); • G4double phi =RandFlat::shoot(HepDouble(0.),HepDouble(twopi)); // isotropic decay angle phi • … But two body decays are okay G4GeneralPhaseSpaceDecay::G4GeneralPhaseSpaceDecay( … G4double costheta = 2.*G4UniformRand()-1.0; G4double phi = 2.0*M_PI*G4UniformRand()*rad; Hadronic Interactions

  11. GEANT4 not transverse symmetric? Beam incident along +x axis. asymmetric in y okay in z GEANT3 okay Hadronic Interactions

  12. Partially debugged GEANT4 Total Energy for 1 GeV/c2 antineutrons in Hydrogen • Energy missing in two body interactions • e.g. 0.12 GeV disappears in p-p pN Hadronic Interactions

  13. Total Energy for 100 GeV/c2 π+ Hadronic Interactions

  14. Other questions • It is not yet clear to me whether these are GEANT4 bugs, my bugs, or not bugs at all. • Crashes for some events with • K- absorption in hydrogen • neutrons produced at rest in tungsten • May be because I copied a small mistake in the GEANT4 guide. • GEANT4 hadronic interactions seem slooooow! • My GEANT3 jobs are typically 5 to 20 times faster than my GEANT4 jobs. • even 1 GeV electrons are 7 times faster • Am I doing something dumb? • May be because GEANT4 does much more? • cuts needed to stop some low energy particles bouncing forever(?). • Irrelevant for complex geometry? Hadronic Interactions

  15. Questions (cont’d) • Somebody here probably knows the answer to some of these: • Does Fluka-Geant3 have any nuclear energy losses? • Are GHEISHA-Geant3/4 nuclear evaporation processes and binding energy losses accurate? • They just “eat” much of the energy, so I have not yet checked the losses in detail. • Why do FLUKA showers have much larger size fluctuations than GHEISHA-Geant3/4? • Will look at some events. Hadronic Interactions

  16. Shower size fluctuations Beam on X axis Y and Z the same. Hadronic Interactions

  17. Summary • GEANT4 hadronic parameterization is a translation and extension of Fortran GHEISHA. • Note: GEANT4 also has theory driven models • Much hard (and much appreciated!) work has gone into this by the GEANT4 team, but clearly they have not had time for complete testing. • Unfortunately, several significant GHEISHA problems have been translated. • Some new problems as well. • There may be other less obvious problems. • “The Central Limit Theorem forgives many sins.” • More work needed. Hadronic Interactions

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