Summary of hadronic tests and benchmarks in ALICE
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Transcript of 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
Proton Thin TargetSimulation 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
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 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 % 0.00 % 0.00 %
256 MeV 0.38 % 0.02 % 0.44 %
597 MeV 0.77 % 0.00 % 0.90 %
800 MeV 1.20 % 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
p
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:pions: (p,Al) @ 597 MeV
Before Now
Parameterised model:nucleons: (p,Al) @ 597 MeV
NowBefore
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
ΩE dd
d2
Double Differentials
GHEISHA
Precompound
Double Differential Ratio Al @ 113
GHEISHA
Precompound
Double Differential Ratio Al @ 256
GHEISHA
Precompound
Double Differential Ratio Fe @ 256
GHEISHA
Precompound
Double Differential Ratio Fe @ 597
GHEISHA
Precompound
Double Differential Ratio Pb @ 597
GHEISHA
Precompound
Double Differential Ratio Pb @ 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 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
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)
ExperimentalSimulated
ExperimentalSimulated
43 MeV 68 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 MeVTest Shield: Iron – Thickness: 20 cm
Preliminary Results: 68 MeVTest Shield: Iron – Thickness: 20 cm
Preliminary Results: 43 MeVTest Shield: Iron – Thickness: 40 cm
Preliminary Results: 68 MeVTest Shield: Iron – Thickness: 40 cm
Preliminary Results: 43 MeVTest Shield: Concrete – Thickness: 25 cm
Preliminary Results: 68 MeVTest Shield: Concrete – Thickness: 25 cm
Preliminary Results: 43 MeVTest Shield: Concrete – Thickness: 50 cm
Preliminary Results: 68 MeVTest 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
G4_03.wrl
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