Data/MC comparison with G4.81 at Very Low Energies

1. Data/MC comparison withG4.81 at Very Low Energies Tancredi.Carli@cern.ch Atlas Combined Test Beam 2004 (slice of ATLAS detector) Period 8, Energies: 1, 2, 3, 5 and 9 GeV, negative pion beam, electrons removed with TRT/Cerenkov), Off-axis muons removed by timing cut, for low energies need cut on last Tile Layer  applied to all energies here… Data are very preliminary ATLAS MC is preliminary (e.g. we are investigating need of Birks law in LAr Calo) 24/1/2007 10k event for each run with 4 different physics list based on G4.81

2. Close to what was in G3-Geisha, uses measured reaction cross-section and spectra from final state from fits to data (likely to have correlations wrong) LHEP : E>25 GeV LEP: <25 GeV Monte Carlo Data Set LHEP (LHEP’ is LHEP with upgraded cross-sections) QGSP (Quark Gluon String-Model) Upgraded production cross-sections + theory driven model for final state, e.g. pi p-> X Bertini cascade Model for intra-nuclear nucleon-nucleon scattering Binary cascade Model for intra-nuclear nucleon-nucleon scattering: only 22 reactions LHEP LHEP LEP 25 GeV QGSP LEP’ QGSP smooth transition between models (decided by random number in certain range) 25 GeV QGSP_BERT LEP’ QGSP Bertini-cascade 25 GeV QGSP_BERT-MODIF 9 LEP’ QGSP Bertini-cascade 5 25 GeV QGSP_BIC LEP’ QGSP Binary-cascade 9 25 GeV

3. Lar-Back Layer Energies first cluster – E = 9 GeV LAr-Middle Lar-Strips Lar-PS Tile-A Tile-BC Tile-D Elay6<0.15 GeV Good description by models, except in Lar2 where there is clear shift Bertini is off (starts and ends too late), Bertini with Emax 9 5 better

4. Layer Energies first cluster – E = 5 GeV Elay6<0.15 GeV Models start and end earlier, again shift in LAr2 QGSP-Bertini = QGSP-BERT-MODIF, decrease Emax a bit down ?

5. Layer Energies first cluster – E = 3 GeV Elay6<0.15 GeV Bertini very good. Why peak in TileBC ? …more mips, nor reaching last layer

6. Layer Energies first cluster – E = 2 GeV Elay6<0.15 GeV BIC start too early, Bertini good

7. Layer Energies first cluster – E = 1 GeV Elay6<0.15 GeV Data sample pretty small…, models more or less identical, probably dominated by ionisation

8. Total Energy in first and second cluster MC shifted to high values Need solve Lar2 problem Birks law ?

9. Lateral Profile in Layer 1 – Eta Direction All MC pretty good Pion shower has e.m. like core Model dependence small

10. Lateral Profile in Layer 1 – Eta Direction All MC pretty good Pion shower has e.m. like core Model a bit too wide ? Note: radial profile correlated with long profile em shower contained in +- 8 strips

11. Lateral Profile in Layer 2 – Eta Direction All MC pretty good Pion shower has e.m. like core Model a bit too wide ? Note: radial profile correlated with long profile em shower contained in +- 3 cells

12. Lateral Profile in Layer 2 – Eta Direction em shower contained in +- 3 cells

13. Conclusion Generally the description of the data by the MC models is not too bad However, there is a shift in Lar2 (also seen in analysis of higher energies) Birk’s law ? …presently investigated ! Bertini cascade gives good description of the data for E<=3 GeV, but fails at for E>9 GeV, shifting upper limit from 9 GeV to 5 GeV gives overall better agreement with data Binary cascade model gives also reasonable description Next steps: Move to version: G4.8.2 Test-out: Birks law Do you suggest something ?