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

2. 2 1.Cherenkov light tracing 2.Lookup table 3.Physical application Outline

3. 3 HADES EMC Hardware: Cherenkov light EM calorimeter 142 * 6 lead glass blocks Physics: e/h separation at high momentum π 0, η reconstruction Sesimbra meeting status: EMC is implemented in HGeant First simulations were started

4. 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: 8.7% / sqrt(E) ~5% / sqrt(E) γ in simulation: γ in reality: old simulations Opal results

5. 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. 6 Tuning results γ 580 MeV cosmics Experimental reference for the tuning  Energy resolution for γ  Same response shown by γ 580 MeV and cosmics

7. 7 Single lead glass module response to different particle species eγπpneγπpn Cherenkov thresholds P π = 98 MeV/c P p = 700 MeV/c

8. 8 e/pi separation at 95% electron efficiency

9. 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 = (x 2 + y 2 ) 1/2, z, θ, energy Make use of THnSparse class as a container Binning: 30 * 30 * 180 * 30 = 5·10 6, populated by 3·10 9 trial photons 2D projections: (z, t) and (energy, z) glass pmt

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

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

12. 12 What is the profit from the Lookup table? 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 Computational time, seconds per event

13. 13 Application: light system at high energies  Pluto cocktail for C + C at 8 AGeV M p = M n = 8.9 M π+ = M π– = M π0 = 1.86 M η = 0.093  Full HADES geometry in front of EMC  Simple reconstruction software was written DigitizationClusteringPair makingRPC matching

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

15. 15 Diphoton invariant mass in CC at 8 AGeV  Cluster matching with RPC hits to reject charged hadrons  Significant background suppression  Clear π 0 -peak  η is not visible, more statistics is mandatory CC 8 AGeV

16. 16 Diphoton invariant mass in CC at 8 AGeV  Cluster matching with RPC hits to reject charged hadrons  Significant background suppression  Clear π 0 -peak  η is not visible, more statistics is mandatory CC 8 AGeV

17. 17 Summary 1.New approach to Cherenkov light tracing 2.Reasonable response both to gamma and hadrons 3.Working Lookup table 4.Simulation software is complete 5.First realistic diphoton spectra for the light system at high energies (π 0 reconstruction is shown ) Outlook: — Further development of the reconstruction software — η reconstruction — Attack heavy systems

18. 18 Additional slides

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

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

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

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

23. 23 EMI 9903B quantum efficiency

24. 24 Lead glass interaction lengths Lead glass Quantity ValueUnitsValueUnits 0.42101 Density 6.22 g cm-3 Nuclear collision length95.9g cm-215.42 cm Nuclear interaction length158.0g cm-225.40 cm Pion collision length122.2g cm-219.64 cm Pion interaction length190.0g cm-230.55 cm Radiation length 7.87 g cm-21.265 cm

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

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

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