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Lead glass simulations

Lead glass simulations. Collaboration Meeting XXI. Eliane Epple, TU Munich Kirill Lapidus, INR Moscow. March 2010 GSI. Outline. Cherenkov light tracing Lookup table Physical application. HADES EMC. Hardware: Cherenkov light EM calorimeter 142 * 6 lead glass blocks Physics:

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Lead glass simulations

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  1. Lead glass simulations Collaboration Meeting XXI Eliane Epple, TU Munich Kirill Lapidus, INR Moscow March 2010 GSI

  2. Outline • Cherenkov light tracing • Lookup table • Physical application

  3. HADES EMC Hardware: Cherenkov light EM calorimeter 142 * 6 lead glass blocks Physics: e/h separation at high momentum π0, ηreconstruction Sesimbra meeting status: EMC is implemented in HGeant First simulations were started

  4. The challenge • Realistic studies require simulation of the electron/gamma and hadron response • Hadron response is complex and can’t be simulated simply via energy deposit in the module • Need for proper Cherenkov light tracing • Previously obtained results are not satisfactory: γ in reality: γ in simulation: ~5% / sqrt(E) 8.7% / sqrt(E) old simulations Opal results

  5. The solution • Use the Light Transport code written by Mikhail Prokudin, ITEP (CBM ECal) • Standalone program outside HGeant • Tuning of the parameters • Light attenuation length in the lead glass • PMT geometry and quantum efficiency • Reflective properties of the lead glass wrapping

  6. Tuning results Experimental reference for the tuning • Energy resolution for γ • Same response shown by γ 580 MeV and cosmics γ580 MeV cosmics

  7. Single lead glass module response to different particle species e γ π p n Cherenkov thresholds Pπ = 98 MeV/c Pp = 700 MeV/c

  8. e/pi separation at 95% electron efficiency

  9. Making things faster: Lookup table instead of the light tracing • Light tracing is very slow: 1.2 s/event for 1 GeV γ • Prepare a lookup table for the probability of the p. e. production • 4D lookup table: t = (x2 + y2)1/2, z, θ, energy • Make use of THnSparse class as a container • Binning: 30 * 30 * 180 * 30 = 5·106, populated by 3·109 trial photons • 2D projections: (z, t) and (energy, z) pmt glass

  10. Testing the approach: Full tracing vs Lookup table Tracing Lookup table gamma, p = 0.1 GeV/c gamma, p = 1 GeV/c pion, p = 0.3 GeV/c neutron, p = 2 GeV/c

  11. Testing the approach: Full tracing vs Lookup table Tracing Lookup table gamma, p = 0.1 GeV/c gamma, p = 1 GeV/c 4% 4.5% • In general Lookup table works well • A bit more effort is needed for correct gamma width • Increase the bin numbers/statistics in the table

  12. What is the profit from the Lookup table? Computational time, seconds per event γ 1 GeV CC 8 AGeV AuAu 1.25 AGeV no EMC — 0.2 0.7 Tracing 1.2 4.9 10.2 Lookup < 0.1 0.6 1.7

  13. Application: light system at high energies • Pluto cocktail for C + C at 8 AGeV Mp = Mn = 8.9 Mπ+= Mπ– = Mπ0 = 1.86 Mη = 0.093 • Full HADES geometry in front of EMC • Simple reconstruction software was written Digitization Clustering RPC matching Pair making

  14. Diphoton invariant mass in CC at 8 AGeV CC 8 AGeV • Employ only calorimeter data • Overwhelming background from hadron misidentification

  15. Diphoton invariant mass in CC at 8 AGeV • Cluster matching with RPC hits to reject charged hadrons • Significant background suppression • Clear π0-peak • ηis not visible, more statistics is mandatory CC 8 AGeV

  16. Diphoton invariant mass in CC at 8 AGeV • Cluster matching with RPC hits to reject charged hadrons • Significant background suppression • Clear π0-peak • ηis not visible, more statistics is mandatory CC 8 AGeV

  17. Summary • New approach to Cherenkov light tracing • Reasonable response both to gamma and hadrons • Working Lookup table • Simulation software is complete • First realistic diphoton spectra for the light systemat high energies (π0reconstruction is shown) • Outlook: • — Further development of the reconstruction software • — ηreconstruction • — Attack heavy systems

  18. Additional slides

  19. Integral Lookup table test Reconstructed diphoton invariant mass for CC 8 AGeV 10k events Tracing Lookup table

  20. Calibrations and corrections for the simulation (to be done)

  21. Correlation of energy deposition and Cherenkov photon yield ~ 10K Cherenkov photons tracked in each module Limited energy range was investigated due to extreme hit multiplicities Deposited energy in module, MeV N_pe = 1785 * (E/GeV) OPAL paper NIM A290 76-94 N_pe = 1800 * (E/GeV)

  22. Study of response to single photons: energy deposition in EMC Deposited energy for 1 GeV photon Energy dependence — whole EMC — 3x3 cluster ▼whole EMC ▼ 3x3 cluster

  23. EMI 9903B quantum efficiency

  24. Lead glass interaction lengths Lead glass QuantityValue Units Value Units <Z/A> 0.42101 Density 6.22 g cm-3 Nuclear collision length 95.9 g cm-2 15.42 cm Nuclear interaction length 158.0 g cm-2 25.40 cm Pion collision length 122.2 g cm-2 19.64 cm Pion interaction length 190.0 g cm-2 30.55 cm Radiation length 7.87 g cm-2 1.265 cm

  25. EMC geometry Top view of one sector 142 identical modules Technical drawing by Polish group

  26. Simple simulation:geometry and Pluto input EMC geometry Pluto Position as present Shower phi (0, 2pi) theta (18, 45) L = 240 cm d x d = 9.2 x 9.2 cm2 sigma_theta = d/L/sqrt(12) sigma_phi = sigma_theta sigma_E/E = 5% / sqrt(E/GeV) C+C @ 8 AGeV 10M events Multiplicities (min. bias) M_pi0 = 1.86 M_eta = 0.093 Diphoton decays only

  27. Diphoton invariant mass • EMC acceptance • spatial & energy smearing of photon pγ > 300 MeV pγ > 500 MeV sigma_eta = 25 MeV sigma_eta = 25 MeV S/B = 11% S/B = 10% M, GeV M, GeV

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