Physics Validation of the Simulation Packages in a LHC-wide effort

Physics Validation of the Physics Validation of the Simulation Packages in a Simulation Packages in a LHC-wide effortLHC-wide effort

Alberto RibonAlberto Ribon

CERN PH/SFT CERN PH/SFT on behalf of the LCG Simulation Physics Validation group

CHEP’04, Interlaken, 27th September 2004

Track 2 “Event Processing” #493

Alberto Ribon, CERN/PH/SFT

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Simulation Project LeaderG.Cosmo

FrameworkA. Dell’Acqua

WPWP

WP

Geant4J.Apostolakis

WPWP

WP

FLUKAIntegration

A.Ferrari

WPWP

PhysicsValidationF.Gianotti

WPWP

WP

ShowerParam

WPWP

GeneratorServicesP.Bartalini

WPWP

Subprojects

Work packages

Geant4Project

FLUKAProject

ExperimentValidation MC4LHC


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LCG physics validation project goals: • compare Geant4, Fluka with the LHC test-beam data

• test coherence of results across experiments and sub-detector technologies

• study simple benchmarks relevant to LHC

• “certify” that simulation packages and framework are ok for LHC physics

• weaknesses and strengths of the packages

More details:

http://lcgapp.cern.ch/project/simu/validation/


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•

• First cycle of electromagnetic physics validation completed at the percent level. We will focus here only on the (most difficult!) hadronic physics validation.

• As for the choice of the Geant4 Physics List, the validation should be targeted to each considered application domain: e.g. for high-energy physics one should consider different observables than, for instance, medical physics, or space science.

• The criteria to consider a simulation “good” or “bad” should be based on the particular application: e.g., for LHC experiments, the main requirement is that the dominant systematic uncertainties for all physics analyses should not be due to the imperfect simulation.

Physics Physics ValidationValidation


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Validation project

Suppose that e.g. for e/ : (G4-test-beam data)~10%

LHC physics simulation

Does this meet LHC physics requirements (e.g. for compositeness) ?

Check with (fast ?) simulations thatthis is good enough

If not :

Needs input/help from the experiment physics groups


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Two main types of test-beam setups:

1. Calorimeters: the typical test-beams (made mainly for detector purposes).

The observables are the convolution of many effects and interactions. In other words, one gets a macroscopic test.

2. Simple benchmarks: typical thin-target setups with simple geometry (made, very often, for validation purposes).

It is possible to test at microscopic level a single interaction or effect.

These two kinds of setup provide complementary information!

Type

Validation Validation setupssetups


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Double-differential neutron production Double-differential neutron production (p,xn)(p,xn)

Proton beam energies: 113, 256, 597, 800 MeV

Neutron detectors (TOF, scintillators) at 5 angles.

Study of the neutron production spectrum (kinetic energy) at fixed angles.


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benchmark studies


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benchmark studies

• ratio simulated / experimental data for data shown on previous slide• error bars include errors from experimental data (stat+syst) and from simulation (stat) - dominated by experimental syst. errors

• typical agreement at level of 1 σ to 2σ

FLUKA

G4: QGSP_BERT

G4: QGSP_BIC


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K. Nakai at al., PRL 44, 1446 (1980)K. Nakai at al., PRL 44, 1446 (1980) D. Ashery et al, PR C23, 2173 (1991)D. Ashery et al, PR C23, 2173 (1991)

pi +/-

thin target (Al, Cu, Au)

detectors

beam monitoring counters

Pion absorption – experimentsPion absorption – experiments

•Nakai – look for gammas emitted after pion absorption

• Ashery – look for transmitted (not absorbed) pions

pi+/- beams ofenergies between

23 – 315 MeV


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Total inelastic cross Total inelastic cross sectionsection


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Absorption Xsection for Absorption Xsection for pi+pi+

both G4 and Fluka show both G4 and Fluka show reasonable agreementreasonable agreement

in some cases Fluka seems in some cases Fluka seems to be a bit betterto be a bit better

difficult to make more difficult to make more conclusions because of big conclusions because of big uncertainties in the uncertainties in the experimental dataexperimental data


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Absorption Xsection for pi-Absorption Xsection for pi-

same remarks as for pi+same remarks as for pi+ for heavy material (Au) the for heavy material (Au) the

shape of the QGSP_BERT shape of the QGSP_BERT quite differentquite different

G4: best agreement for G4: best agreement for ‘medium-weight’ materials‘medium-weight’ materials


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Hadronic interactions in ATLAS pixel Hadronic interactions in ATLAS pixel test-beamtest-beam

180 GeV/c nominal + beam

Geant4 Geometry. Use the same Geometry also with Fluka,using FLUGG (interface between the Transportation and Physics of Fluka and Geant4 Navigation of the Geometry).


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Number of reconstructed tracksNumber of reconstructed tracks


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Pseudorapidity distributionPseudorapidity distribution


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Ratio max Eloss / total ElossRatio max Eloss / total Eloss

QGSP is in excellent agreementwith data.


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Cluster sizeCluster size QGSP producestoo narrow clusters.FLUKA, LHEPand QGSC are in good agreement withdata.

In conclusion,FLUKA, Geant4are in reasonablegood agreementwith the data, but some observables canbe improved.


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:

ATLAS:

HEC : copper + LAr HEC1 + HEC2, 4 longitudinal compartments 6-150 GeV for electrons; 10-200 GeV for charged pions; 120, 150, 180 GeV for muons.

Tilecal : iron + scintillator tile 2 extended barrel + 1 barrel + barrel 0 modules 20-180 GeV electrons and charged pions; 1, 2, 3, 5, 9 GeV charged pions.

CMS:

combined ECAL + HCAL : ECAL : prototype of 7 x 7 PbWO4 crystals HCAL : copper + scintillator tile each tile is read out independently Max magnetic field of 3 T 10-300 GeV muons, electrons, and hadrons.

LHC hadronic calorimeter test-beams


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ATLAS HEC test beam setup


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0.25 0.65

extended barrelmodule

extended barrelmodule

η=0.25η=0.65

ATLAS Tilecal test beam setup


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CMS HCAL & ECAL test beam setup

Crystal 25


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energy resolution of pions

beamtestEsimulationE


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e/π ratio

beamtest

esimulation

e


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ATLAS HEC: leakage


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ATLAS HEC: energy deposition

There are 4 longitudinal segments: 2 in HEC1 and 2 in HEC2.

F is the fraction of the total energy deposition in each layer.


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ATLAS Tile: π shower profile

barrel / Etot

EB + M0 / Etot

M0

barrel

EB

EB


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CMS longitudinal shower profile in HCAL for 100 GeV pions


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Conclusions Geant4 electromagnetic physics has been already

validated at percent level. In the next future, we will try to push it at the permil level.

First round of hadronic physics validation has been completed, with good results.

For the observables we have checked in the case of the simple benchmarks (pixels, neutron double differential, pion absorption) there is a reasonable agreement between data and both Geant4 and Fluka, more or less at the same level.

For the calorimeter test-beams, Geant4 describes well the pion energy resolution, σ/E, and the ratio e/.

The shape of hadronic showers still needs further improvements.

Geant4 studies of radiation background in the LHC caverns are in progress, and they will be soon compared with Fluka.

Physics Validation of the Simulation Packages in a LHC-wide effort

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