Lead glass simulations

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