Summary of hadronic tests and benchmarks in ALICE Isidro González CERN EP-AIP/Houston Univ. Geant4 workshop 2002 30 - September - 2002

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

ALICE Low momentum particle is of great concern for central ALICE and the forward muon spectrometer because: ALICE has a rather open geometry (no calorimetry to absorb particles) ALICE 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 2001-41 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 Not used yet! Specialised cross section: G4ProtonInelasticCrossSection

Conservation Laws Systems in the reaction: Conservation Laws: Target nucleus Incident proton Emitted particles Residual(s): unknown in the parameterised model Conservation Laws: Energy (E) Momentum (P) Charge (Q) 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 Bres and Qres Assume E-P conservation Eres and Pres are not correlated  unphysical values for Mres Aluminum is the worst case Energy Q<0 B<0 Nneu < 0 113 MeV 0.00 % 256 MeV 0.38 % 0.02 % 0.44 % 597 MeV 0.77 % 0.90 % 800 MeV 1.20 % 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 Include some plots!

Azimuthal Distributions x y z  j 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 p and nucleons

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

Parameterised model: jpions: (p,Al) @ 597 MeV Before Now

Parameterised model: jnucleons: (p,Al) @ 597 MeV Before Now

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 Al @ 113 Precompound GHEISHA

Double Differential Ratio Al @ 256 Precompound GHEISHA

Double Differential Ratio Fe @ 256 GHEISHA Precompound

Double Differential Ratio Fe @ 597 GHEISHA Precompound

Double Differential Ratio Pb @ 597 Precompound GHEISHA

Double Differential Ratio Pb @ 800 Precompound GHEISHA

Conclusions Proton Several bugs were found in GEANT4 during proton inelastic scattering test development. Most of them are currently solved. The parameterised model cannot satisfy the physics we require. 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 View Side 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 Show the plot of the two energy spectra….

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

Energy Spectrum Simulation (Consistency check) 43 MeV 68 MeV Experimental Simulated Experimental Simulated

Simulation Physics Electromagnetics: for e± and g 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 3He 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