Checking Basic Characteristics of Hadronic Shower Parameterizations in GHEISHA / GEANT4

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