Summary of hadronic tests and benchmarks in ALICE Isidro González CERN EP-AIP/Houston Univ. Geant4 workshop Oct

Summary ALICE interest Proton thin-target benchmark – Experimental and simulation set-up – Conservation laws – Azimuthal distributions – Double differential cross sections – Conclusions Neutron transmission benchmark – Expermintal and simulation set-up – Flux distribution – Conclusions

Experimental Setup Beam energies: 113, 256, 597 & 800 MeV Neutron detectors at: 7.5º, 30º, 60º, 120º & 150º Materials: aluminum, iron and lead Detector angular width: 10º Thin target only one interaction Data information from Los Alamos in: Nucl. Sci. Eng., Vol. 102, 110, 112 & 115

ALICE Low momentum particle is of great concern for central ALICE and the forward muon spectrometer because: – has a rather open geometry (no calorimetry to absorb particles) – has a small magnetic field – Low momentum particles appear at the end of hadronic showers Residual background which limits the performance in central Pb-Pb collisions results from particles "leaking" through the front absorbers and beam-shield. In the forward direction also the high-energy hadronic collisions are of importance.

Proton Thin Target Experimental Set-Up

Proton Thin Target Simulation Set-Up Revision of ALICE Note with Geant4.4.1 (patch 01) Processes used: – Transportation – Proton Inelastic: G4ProtonInelasticProcess Models: – Parameterised: G4L(H)EProtonInelastic – Precompound: G4PreCompoundModel Geometry used: – Very low cross sections:  Thin target is rarely “seen”  CPU time expensive – One very large material block  One interaction always takes place  Save CPU time – Stop every particle after the interaction  Store its cinematic properties

GHEISHA Physics List theParticleIterator->reset(); while ((*theParticleIterator)()) { G4String particleName = theParticleIterator->value()->GetParticleName(); G4ProcessManager* pmanager = particle->GetProcessManager(); if (particleName == "proton") { G4ProtonInelasticProcess* theInelasticProcess = new G4ProtonInelasticProcess("Had_Inelastic_proton"); G4LEProtonInelastic* theLEInelasticModel = new G4LEProtonInelastic; G4HEProtonInelastic* theHEInelasticModel = new G4HEProtonInelastic; theInelasticProcess->RegisterMe(theLEInelasticModel); theInelasticProcess->RegisterMe(theHEInelasticModel); pmanager->AddDiscreteProcess(theInelasticProcess); }

Precompound Physics List G4PreCompoundModel* thePreEquilib = new G4PreCompoundModel(new G4ExcitationHandler); theParticleIterator->reset(); while ((*theParticleIterator)()) { G4String particleName = theParticleIterator->value()->GetParticleName(); G4ProcessManager* pmanager = particle->GetProcessManager(); if (particleName == "proton") { G4ProtonInelasticProcess* theInelasticProcess = new G4ProtonInelasticProcess("Had_Inelastic_proton"); theInelasticProcess->RegisterMe(thePreEquilib); pmanager->AddDiscreteProcess(theInelasticProcess); }

Conservation Laws Systems in the reaction: 1. Target nucleus 2. Incident proton 3. Emitted particles 4. Residual(s): unknown in the parameterised model Conservation Laws: 1. Energy (E) 2. Momentum (P) 3. Charge (Q) 4. Baryon Number (B)

Conservation Laws in Parameterised Model The residual(s) is unknown  It must be calculated – Assume only one fragment Residual mass estimation: – Assume B-Q conservation: We found negative values of B res and Q res – Assume E-P conservation E res and P res are not correlated  unphysical values for M res Aluminum is the worst case EnergyQ<0B<0N neu < MeV0.00 % 256 MeV0.38 %0.02 %0.44 % 597 MeV0.77 %0.00 %0.90 % 800 MeV1.20 %0.00 %1.50 %

Conservation Laws in the Precompound Model There were some quantities not conserved in the initial tested versions Charge and baryon number are now conserved! Momentum is exactly conserved Energy conservation: – Is very sensitive to initial target mass estimation  Use G4NucleiProperties – Width can be of the order of a few MeV

Azimuthal Distributions  defined in the plane perpendicular to the direction of the incident particle (x) Known bug in GEANT3 implementation of GHEISHA Expected to be flat Plotted for different types of  and nucleons x y z 

Azimuthal Distributions  distributions are correct! However… Parameterised model: – At 113 & 256 MeV: No  is produced – At 597 & 800 MeV: Pions are produced in Aluminium and Iron (Almost) no  is produced for Lead Precompound model: – Not able to produce , they should be produced by some intranuclear model

Parameterised model:  nucleons for 113 & 256 MeV

Parameterised model:  pions : 597 MeV Before Now

Parameterised model:  nucleons : 597 MeV Now Before

Double differentials Real comparison with data We plot Which model is better?… Difficult to say – GHEISHA is better in the low energy region (E < 10 MeV) – Precompound is better at higher energies (10 MeV < E < 100 MeV) – None of the models reproduce the high energy peak

Double Differentials GHEISHA Precompound

Double Differential Ratio 113 GHEISHA Precompound

Double Differential Ratio 256 GHEISHA Precompound

Double Differential Ratio 256 GHEISHA Precompound

Double Differential Ratio 597 GHEISHA Precompound

Double Differential Ratio 597 GHEISHA Precompound

Double Differential Ratio 800 GHEISHA Precompound

Conclusions Proton Several bugs were found in GEANT4 during proton inelastic scattering test development The parameterised model cannot satisfy the physics we require. Why??? Precompound model agreement with data improved for – Light nuclei – Low incident energies – Low angles An intranuclear cascade model would be very welcome – May solve the double differentials disagreement – May produce correct distribution of particle flavours

Tiara Facility

Target Views Top ViewSide View

Simulation Geometry Block of test shield placed at z > 401 cm Different test shield material and thickness: – Iron: 20 cm 40 cm – Concrete: 25 cm 50 cm 2 incident neutrons energy spectra. Peak at: – 43 MeV – 68 MeV

Simulation Set-up y x Volumes to estimate the flux (“track length” method) x = 0, 20 & 40 cm 401 cm

Energy Spectrum Simulation (Consistency check) Experimental Simulated Experimental Simulated 43 MeV68 MeV

Simulation Physics Electromagnetics: for e ± and  Neutron decay Hadronic elastic and inelastic processes for neutron, proton and alphas – Tabulated (G4) cross-sections for inelastic hadronic scattering – Precompound model is selected for inelastic hadronic scattering Neutron high precision (E < 20 MeV) code with extra processes: – Fission – Capture 1 million events simulated for each case

Preliminary Results: 43 MeV Test Shield: Iron – Thickness: 20 cm

Preliminary Results: 68 MeV Test Shield: Iron – Thickness: 20 cm

Preliminary Results: 43 MeV Test Shield: Iron – Thickness: 40 cm

Preliminary Results: 68 MeV Test Shield: Iron – Thickness: 40 cm

Preliminary Results: 43 MeV Test Shield: Concrete – Thickness: 25 cm

Preliminary Results: 68 MeV Test Shield: Concrete – Thickness: 25 cm

Preliminary Results: 43 MeV Test Shield: Concrete – Thickness: 50 cm

Preliminary Results: 68 MeV Test Shield: Concrete – Thickness: 50 cm

Bonner Sphere Geometry Sensitive volume made of 3 He and Kr Moderator made of Poliethylene Several moderator sizes considered

Bonner Sphere Simulation Need to use: – Spheres (rarely used in HEP) – Boolean solids (Cilinder – Sphere) Bug in tracking with spheres – Already reported We have not yet tested boolean solids

Conclusions Neutron The MC peak, compared to the data, is: – narrower – higher Though the simulation does not match the data: – Iron simulation shows better agreement than Concrete – For concrete 43 MeV seems better than 68 MeV Higher statistics will come soon Bonner Sphere detector simulation could not be done with previous GEANT4 releases Note: Linux gcc 2.95 supported compiler used