Summary of hadronic tests and benchmarks in ALICE

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

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 TargetExperimental 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 Stopevery particle after the interaction Store its cinematic properties Proton Thin TargetSimulation Set-Up

Systems in the reaction: 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

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

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

y  x z Azimuthal Distributions • 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 & 256MeV: No p is produced • At 597 & 800MeV: • 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

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

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

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 Precompound GHEISHA

Double Differential Ratio Fe @ 597 Precompound GHEISHA

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 • 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

Top View Side View Target Views

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

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

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

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 MeVTest Shield: Iron – Thickness: 20 cm

Preliminary Results: 43 MeVTest Shield: Concrete – Thickness: 25 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

Summary of hadronic tests and benchmarks in ALICE

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