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

2. 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

3. 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.

4. Proton Thin Target Experimental Set-Up

5. 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
Not used yet!
Specialised cross section:
G4ProtonInelasticCrossSection

6. 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)

7. 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 %

8. 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!

9. Azimuthal Distributionsx 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

10. 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

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

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

13. 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

14. Double Differentials
GHEISHA
Precompound

15. Double Differential Ratio Al @ 113
Precompound
GHEISHA

16. Double Differential Ratio Al @ 256
Precompound
GHEISHA

17. Double Differential Ratio Fe @ 256
GHEISHA
Precompound

18. Double Differential Ratio Fe @ 597
GHEISHA
Precompound

19. Double Differential Ratio Pb @ 597
Precompound
GHEISHA

20. Double Differential Ratio Pb @ 800
Precompound
GHEISHA

21. 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

22. Tiara Facility

23. Target Views
Top View
Side View

24. 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….

25. 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

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

27. 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

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

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

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

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

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

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

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

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

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

37. 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

38. 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