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: 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

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

Summary of hadronic tests and benchmarks in ALICE

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