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

Dominik Dannheim,André Sailer (CERN)

Incoherent pairs andγγ hadrons

at 500 GeV and 3 TeV

WG-6 meeting17. May 2011

Updated 18. May for gghadrons: added information on hadronisation models; added 2d color plots for pt vs. theta

215. May 2011 Backgrounds at 500 GeV

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


Occupancies at 3 TeV

Critical regions


Occupancies at 500 GeV


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


γγhadrons 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


Invariant mass of final-state particles


Transverse momentum and polar angle (3 TeV)


Transverse momentum and polar angle (500 GeV)


Polar angle of charged particles


Momentum of charged particles


Number of particles per bx


Visible energy per bx


Total energy + occupancy per bx at 3 TeV===============================================================Pythia 3 TeV sample (D. Schulte) 3.2 events / bxCLIC_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


Total energy + occupancy per bx at 500 GeV===============================================================Pythia 500 GeV sample (D. Schulte) 0.3 events / bxCLIC_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


Cell occupancies at ECAL+plug front

• Consider only direct hits from γγhadrons• 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


Cell occupancies at ECAL+plug front face


Cell occupancies at ECAL+plug bottom face

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• Performed optimization of beam pipe and vertex region,based on direct hits from incoherent pairs

• New detector layout for 500 GeV with outer radius of central beam pipe at 24 mm, cf. André’s presentation for details

• Validated γγhadrons sample for 500 GeV• 20x less energy and occupancy in the detector, compared

to the 3 TeV sample• Up to 40% cell-occupancy per train in ECAL plug at 3 TeV

in fast simulation


Conclusions

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

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