Incoherent pairs and γγ  hadrons at 500 GeV and 3 TeV WG-6 meeting 17. May 2011

1. Incoherent pairs andγγ hadronsat 500 GeVand 3 TeVWG-6 meeting17. May 2011 Dominik Dannheim,André Sailer(CERN) Updated 18. May for gghadrons: added information on hadronisationmodels; added 2d color plots for pt vs. theta

2. Geometry optimisation using incoherent pairs • 1 bunch train worth of incoherent pairs • Only look at direct hits, therefore apply cuts: • pT>8 MeV • θ > 2o • Resulting sample sizes: • √s=3 TeV: 7.72M particles • √s=500 GeV: 2.75M particles • Fast simulation of direct hits: follow particles on heliceswith CLIC_ILD geometry and B-field • Move straight section of beam pipe closer to IP for 500 GeV,keeping projective beam pipe in forward region • New radius of beam pipe and inner vertex layer is given byconstraint that occupancies in critical regions are similarfor 500 GeV as for the 3 TeV geometry • Critical regions are: • Edge where beam pipe becomes conical • Most forward region of innermost vertex layer Backgrounds at 500 GeV

3. Occupancies at 3 TeV Critical regions Backgrounds at 500 GeV

4. Occupancies at 500 GeV Backgrounds at 500 GeV

5. Occupancies at 500 GeV and 3 TeV  Acceptable occupancies at 500 GeV in critical regions, when moving beam pipe and innermost vertex layer closer to IP by 6 mm Backgrounds at 500 GeV

6. γγhadrons samples • sqrt(s)=3 TeV sample • Daniel Schulte 2010 • GUINEA-PIG + Pythia • Default hadronisation parameters in Pythia • Mγγ>2 GeV • 67k events, 3.2 events / bx • Standard sample for CDR production • sqrt(s)=500 GeV sample • Daniel Schulte 2011 • GUINEA-PIG + Pythia • OPAL tuning for hadronisation parameters in Pythia • Mγγ>2 GeV • 298k events, 0.3 events / bx Backgrounds at 500 GeV

7. Invariant mass of final-state particles Backgrounds at 500 GeV

8. Transverse momentum and polar angle (3 TeV) Backgrounds at 500 GeV

9. Transverse momentum and polar angle (500 GeV) Backgrounds at 500 GeV

10. Polar angle of charged particles Backgrounds at 500 GeV

11. Momentum of charged particles Backgrounds at 500 GeV

12. Number of particles per bx Backgrounds at 500 GeV

13. Visible energy per bx Backgrounds at 500 GeV

14. Total energy + occupancy per bx at 3 TeV =============================================================== Pythia 3 TeV sample (D. Schulte) 3.2 events / bx CLIC_ILD_CDR, B = 4 T =============================================================== Section E_vis/bx [GeV] # part./bx # ch. part./bx =============================================================== no cuts 1365.2 102.42 50.05 |theta| > 5.73 deg 62.1 58.69 27.60 --------------------------------------------------------------- LUMI-CAL 101.5 18.76 9.13 --------------------------------------------------------------- Pixel-Forward - 29.86 14.33 Pixel-Barrel - 42.36 19.61 Pixel-all - 54.07 25.30 --------------------------------------------------------------- CAL-PLUG+EC 59.8 41.96 18.00 CAL-Barrel 3.6 11.02 0.25 CAL-all 62.2 50.03 18.18 --------------------------------------------------------------- TRK-Forward - 41.28 15.50 TRK-Barrel - 24.58 11.85 TRK-all - 50.58 21.51 =============================================================== Note: 70% more background now in ECAL, after including the plug with Ri=242 mm Backgrounds at 500 GeV

15. Total energy + occupancy per bx at 500 GeV =============================================================== Pythia 500 GeV sample (D. Schulte) 0.3 events / bx CLIC_ILD_CDR modified vertex region, B = 4 T =============================================================== Section E_vis/bx [GeV] # part./bx # ch. part./bx =============================================================== no cuts 13.3 5.01 2.54 |theta| > 5.73 deg 3.5 3.89 1.91 --------------------------------------------------------------- LUMI-CAL 3.5 0.76 0.40 --------------------------------------------------------------- Pixel-Forward - 1.88 0.95 Pixel-Barrel - 3.22 1.56 Pixel-all - 3.65 1.78 --------------------------------------------------------------- CAL-PLUG+EC 3.2 2.62 1.17 CAL-Barrel 0.2 0.78 0.01 CAL-all 3.4 3.20 1.18 --------------------------------------------------------------- TRK-Forward - 2.81 1.10 TRK-Barrel - 1.50 0.77 TRK-all - 3.37 1.48 =============================================================== ~20x less energy and occupancy at 500 GeV, compared to 3 TeV Backgrounds at 500 GeV

16. Cell occupancies at ECAL+plug front • Consider only direct hits from γγhadrons • Fast simulation for CLIC_ILD_CDR geometry: • Follow all final state particles in B-field through detector • No energy loss in material • Simplified geometry for ECAL plug cells: • ΔR x ΔRφ x Δz = 5 mm x 5 mm x 6 mm • Create one hit if particle crosses the corresponding cell •  overestimation of real hit rate Backgrounds at 500 GeV

17. Cell occupancies at ECAL+plug front face Backgrounds at 500 GeV

18. Cell occupancies at ECAL+plugbottom face Backgrounds at 500 GeV

19. Conclusions • Performed optimization of beam pipe and vertex region,based on direct hits from incoherent pairs • New detector layout for 500 GeVwith outerradius of central beam pipe at 24 mm, cf. André’s presentation for details • Validated γγhadrons sample for 500 GeV • 20x less energy and occupancy in the detector, compared to the 3 TeVsample • Up to 40% cell-occupancy per train in ECAL plug at 3 TeVin fast simulation Backgrounds at 500 GeV