Photon reconstruction and calorimeter software

1. Photon reconstruction and calorimeter software Mikhail Prokudin

2. Outline • Calorimeter software development • photon reconstruction • cluster finder • simple reconstruction • UrQMD events • matching • Calorimeter drawing tools • Cluster fitting • requirements • Conclusions • Next steps

3. Photon reco. Requirements • Robust reconstruction of single photons • Two close photons case: • robust reconstruction of parameters in case two separate maximums • separation one/two photons in case of one maximum • Fast!

4. Cluster formation Remove maximums near charged tracks real tracking Precluster: formed near local maximum cut on maximum energy find maximum 2x2 matrix near maximum add a neighbor to local maximum cell with minimal energy deposition to add inromation check precluster energy >0.5GeV Cluster: group of preclusters with common cells Requirements Clusters should be large information for unfolding Clusters should be small hadrons background Cluster finder 4870 Central UrQMD Au+Au 25GeV CbmEcalClusterFinderV1. At SVN

5. Cluster finder performance Benchmark • 2x1 GeV photons • 3x3 cm cells • inner calorimeter region • 2-10° angle • geometry of inner calorimeter region

6. Simple reconstruction • Energy: • calibration • only energy in scintillator is visible • Position: • S-curves • χ2 calculation for reconstructed photon CbmEcalRecoSlow. At SVN

7. UrQMD events with simple reco Gamma spectra Invariant mass spectra True Mixed Subtraction of mixed events is necessarily!

8. Simple reconstruction • Robust reconstruction of single photons • Two close photons case: • occupancy • robust reconstruction of parameters in case two separate maximums • separation one/two photons in case of one maximum • Fast! • Need more complex reconstruction!

9. Why? check origin of cluster neutron clusters physics processes π0 and η decays prompt photons … Most simple method at moment Energy deposition in the cluster > 70% of cluster energy γ/e is secondary also look for mother showers started before the calorimeter treated correctly loss clusters with more than one maximums Matching CbmEcalMatching. At SVN

10. Matching. Usage example π0 η π0 born after IP (conversion)

11. Calorimeter drawing tool • Draw • calorimeter structure • energy deposition in calorimeter • reconstructed tracks • and energies • reconstructed photons • energies • and matched MC particles • clusters • found approximation quality • and χ2 of cluster • MC tracks • type (photon, neutron …) • energy • …and all at one picture!

13. Calorimeter drawing tools • Photons • MC • Reconstructed • * • (Anti) neutrons • Charged tracks • Reconstructed • * • MC • Secondary • Photons • Electrons CbmEcalQualityCheck. At SVN

14. Robust reconstruction of single photons Two close photons case: robust reconstruction of parameters in case two separate maximums separation one/two photons in case of one maximum χ2 criteria all analyzed approaches have failed to reconstruct photons energy/position correctly χ2 shape should not depend on photon’s energy same value for efficiency cut separation power of one/two photons in case of one maximum as a criteria example: with 95% efficiency for clusters formed by single photon Fitter requirements

15. CbmEcalRecoSlow current version at SVN no so slow actually! 40 sec per UrQMD event first approximation CbmEcalRecoSimple χ2minimization minimizer TFitterMinuit shower shape (Epred) shower lib σ2 formula Realization of fitter

16. Shower width h4 • Energy deposition in cluster cells are not independent • storing of RMS in shower library useless • Analytical formula • with correlation • ALICE • σ2=c0(Emeas+c1) • no correlations! • PHENIX • σ2=c0(Emeas(1-Emeas/Ecluster)(1+k  sin4θEcluster)+c1) • correlations are in • Angle dependence • shower library h5 h5 h4

17. σ2 formula declared in configuration file … and parameters too for easy change without recompilation different formulas for different cell types … to maintain commonness Sum of photon’s energies fixed to energy of cluster a switch in configuration file Parameters space is huge σ2 formula best cn could be computed if σ2 formula is fixed also parameters of cluster finder # Number of cells types for reconstruction types=4 #Number of constants for each type consts=2 # Use Ecluster, Emeas and Epred for measured cluster energy, measured cell energy and predicted cellenergy respectively c0_1=0.008 c1_1=0.0016666 c0_2=0.008 c1_2=0.00345 c0_3=-1111 c1_3=-1111 c0_4=0.008 c1_4=0.0043333 sigma_1=c1*(Emeas*(1-Emeas/Ecluster)+c0) sigma_2=c1*(Emeas*(1-Emeas/Ecluster)+c0) sigma_3=-1111 sigma_4=c1*(Emeas*(1-Emeas/Ecluster)+c0) # if chi2 for cluster is less than no fitting chi2th=-1111 # Max iterations in fitting process maxiterations=1000 # Steps for calculation of gradients estep=0.0001 cstep=0.0005 # Fix sum of energies of cluster particles to energy of cluster fixclusterenergy=1 # # Cluster finder stuff # # Maximums belong to charged tracks should excluded? removecharged=1 # Minimum precluster energy minclustere=0.3 # Minimum energy of precluster maximum minmaxe=0.2 # An algorithm for preclustering: 0 --- default, 1 --- PHENIX like, # 2 --- ALICE like, 3 --- default, but remove low energy cells preclusteralgo=0 # Minimum cell energy mincelle=0.020 # Minimum size of precluster minsize=4 # Attach to cluster nearby cells with Edep>fMinCellE attachcells=0.1 σ2 formula Example of configuration file

18. Photon reconstruction. Merged photons Simple reconstruction Cluster fitting Fitting of clusters with two maximums allows us disentangle photons! σ2 formula and parameters does not require much tuning!

19. Robust reconstruction of single photons Two close photons case: robust reconstruction of parameters in case two separate maximums separation one/two photons in case of one maximum χ2 criteria all analyzed approaches have failed to reconstruct photons energy/position correctly χ2 shape should not depend on photon’s energy same value for efficiency cut separation power of one/two photons in case of one maximum as a criteria example: with 95% efficiency for clusters formed by single photon Fitter requirements

20. χ2distributions. Single photons σ2=c0(Emeas+c1) σ2=c0(Emeas(1-Emeas/Ecluster)+c1) c1=0.0005 95% 1 GeV 95% 4 GeV 95% 1 GeV 95% 4 GeV Shape of χ2 for each energy looks Ok, but cut with 95% efficiency has different value! Need a different σ2 formula!

21. Rejection power. Inner region σ2=c0(Emeas+c1) σ2=c0(Emeas(1-Emeas/Ecluster)+c1)

22. Rejection power. Outer region σ2=c0(Emeas+c1) σ2=c0(Emeas(1-Emeas/Ecluster)+c1) Reconstruction in outer region is most sensible to σ2 formula!

23. Conclusions • Calorimeter software development in progress • Cluster finder: CbmEcalClusterFinderV1 • Reconstruction: CbmEcalRecoSimple • and CbmEcalRecoSlow • Matching: CbmEcalMatching • Quality check: CbmEcalQualityCheck

24. Conclusions • Photons reconstruction • simple procedures are ready to use • more complicated procedures • not too slow • fit clusters with more than one maximum • still have limited usability • σ2 formula • bad cluster rejection • not trivial • All presented calculations done using 2 computers • UrQMD transport, reconstruction, etc. • 3.0 GHz Core 2 Duo • 2.0 GHz Core 2 Duo (My laptop)

25. Next steps • Reconstruction tuning • Detector optimization • geometry • segmentation • Detailed sensitivity studies for process with photons • π0, η,χc … • e/π separation with real tracking • Detailed detector geometry • construction details • light collection efficiency