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Reconstruction of photons for CBM CALO system

Reconstruction of photons for CBM CALO system. Prokudin Mikhail, ITEP. First approximation energy calibration position S-curves Cluster unfolding shower shape shower library. LHCb like methods Pure γ , no background Simple and easy to check Test site for shower library routines

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Reconstruction of photons for CBM CALO system

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  1. Reconstruction of photons for CBM CALO system Prokudin Mikhail, ITEP

  2. First approximation energy calibration position S-curves Cluster unfolding shower shape shower library LHCb like methods Pure γ, no background Simple and easy to check Test site for shower library routines Could be done in few month Procedure of γ reconstruction • ALICE-like methods • Require much more effort • CALO parameters should be fixed? We are starting from simple algorithms!

  3. Why calibration for MC? Visible energy/energy of γ depends on cluster size currently we use maximum 2x2 cells of 3x3 cluster to minimize the background incident angle (θ) energy with different energies (0.49,1, 4, 9, 16,25 GeV) withθ uniformly distributed between θmin and θmax to cover all possible incident angles for each calorimeter section Calibration procedure • γsources • Directγgeneration in front of the calorimeter • UrQMD: most of γ’s from π0 decays • see below Automated procedure exists! See ECAL WiKi page: http://cbm-wiki.gsi.de/cgi-bin/view/Ecal/WebHome

  4. Angle dependence Energy in ECAL+PS scintillator for 2x2 cluster vs. tanθ. E=16GeV • Fitted p0+tan(θ) p1 • One fit for each energy/calorimeter section • P0 and P1 depend on energy! GeV

  5. P0 and P1energy dependence P0 P1 a=0.002833±1.59e-4 b=0.08788±5.03e-5 a=0.003398±4.61e-4 b=-0.005302±1.36e-4

  6. UrQMD calibration. Procedure • Full UrQMD event • Select γ’s via MC information • Find appropriate cell in calorimeter • Fit signal for each energy/θ • iterative fitting • unsymmetrical ranges • left boundary is fixed • right is function of energy/θ • occupancies!!! • a lot of fine tuning!!! • [-3δ,+1.2δ] in example This procedure is not used in γreconstruction at the moment

  7. Position reconstruction • Asymmetry • A=(ER-EL)/E3x3 • S-curve • x=f(A, θx, Energy) • θx=ATan(xcell/z) • splines are used for approximation • regularization to decrease statistical errors • Large amount of data required • use one shower several times

  8. S-curve and independence of coordinates S-curve for Ys. X[60,90] −S-curve for Ys. X[150,180] X Asymmetry X,Y can be reconstructed independently with same data!

  9. S-curve dependence on energy and θ X X Asymmetry Asymmetry S-curves information already available with CbmRoot2 framework. Usage example: CbmEcalAnalysisDS class

  10. Position reconstruction precision single photons with energy=1GeV single photons with energy=9GeV RMS 0.6576 RMS 0.3492

  11. Precision for different cells RMS 0.228 RMS 0.419 RMS 0.809 3x3 6x6 12x12

  12. Reconstruction: first attempt • Calibration with single photons used for energy reconstruction • S-curves used for position reconstruction • CbmEcalSCurveLib class • No cluster unfolding • 20k UrQMD central events Au+Au 25GeV • MC information for photon presence used • no peak searching • only photons with energy > 0.5GeV in

  13. Energy reconstruction quality Ereco-EMC<1.5δ Only photons with energy>0.5GeV in front of the calorimeter. Unfolding procedure is necessary!

  14. Results… • Calibration procedures • S-curves • CbmEcalSCurveLib • Quality of first approximation … and next steps • Shower library • Cluster unfolding

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