TRDTRDMC TuningMC Tuning

(Geant3 vs. Geant4)(Geant3 vs. Geant4)

Wim de Boer, Martin Brückel, Florian Hauler, Levin Jungermann, Mike Schmanau, Valery Zhukov

IEKP - Universität Karlsruhe (TH)

01.04.2003 TRD-Meeting, CERN Wim de Boer, Mike Schmanau, Valery Zhukov 2

Testbeam Testbeam at PS (Nov. 2002)at PS (Nov. 2002)

Testbeam:3 GeV Electrons12.5 GeV Protons 2x4 TRD modules=8 layers

01.04.2003 TRD-Meeting, CERN Wim de Boer, Mike Schmanau, Valery Zhukov 3

MotivationMotivationProblem: Energy loss summed over all layers of the TRD detector well tuned in AMS02 MC, but energy loss for individual layers not good.

Solution: get most realistic physical model (GEANT4) OR get good agreement with some parametrization (GEANT3, present AMS02)

Real problem believed to be: geometry of radiator (fibres) cannot be simulated realistically. Tails of energy loss of protons very important!

Protons x10-5

PositronsBoth Geant3 and 4 not fitting wellelectron data for first 4 layers

Energy loss

01.04.2003 TRD-Meeting, CERN Wim de Boer, Mike Schmanau, Valery Zhukov 4

Geant3 Geant4Geant3 Geant4

Parameters: a table parametrizingdifferential photon spectrum d Nγ /dθγ dΕγ (Used in AMS02 MC)

Geometry: radiation produced inradiator with fluctuating thicknessto simulate fibers. Only parameters:Density ρ and effective foil thickness d(d > fiber thickness due to angle > 0)(Geant4 Class: G4irregularXTRadiator)(Stand Alone Code from GEANT4)

01.04.2003 TRD-Meeting, CERN Wim de Boer, Mike Schmanau, Valery Zhukov 5

Tuning GEANT4 ParametersTuning GEANT4 Parameters

3.4200.0487

3.9200.066

3.4150.0485

5.3100.0484

9.480.0483

2.8150.062

8.8100.061

15.180.060

χ2/dfFoilthickness[µm]

Radiator density [g/cm3]

Parame-ter set

χ2= sum of χ2 for each layer for energy loss between 5 and 35 keV

01.04.2003 TRD-Meeting, CERN Wim de Boer, Mike Schmanau, Valery Zhukov 6

Comparison with dataComparison with data

01.04.2003 TRD-Meeting, CERN Wim de Boer, Mike Schmanau, Valery Zhukov 7

Chi2 vs Layer for 8 different parameter sets

01.04.2003 TRD-Meeting, CERN Wim de Boer, Mike Schmanau, Valery Zhukov 8

ConclusionConclusion

For understanding proton background in positron flux,energy loss needs to be understood (especially tails of proton!)

Geant4 has more realistic model, but needs tuning as well. To believe in MC over large energy range, one needs not only good fit of total energy loss, but also of energy loss per layer.

Would like to see tuning effort of both GEANT3 and GEANT4to large TRD test data set of 2001, which covers largeenergy range.