Angular resolution study of isolated gamma with GLD detector simulation

1. Angular resolution study of isolated gamma with GLD detector simulation 2007/Feb/5 ACFA ILC Workshop M1 ICEPP, Tokyo Hitoshi HANO On behalf of the Acfa-Sim-J Group

2. Contents • Introduction • Angular Resolution Study • Position Resolution of ECAL cluster • Direction of Reconstructed gamma • Calorimeter Component Dependence • Cell size Dependence • Material Dependence • Summary

3. Measurement of the direction of non-pointing photon is important for GMSB (gauge mediated supersymmetry breaking) scenarios. IP Motivation and PFA Analysis decay length : [m] • To identify a non-pointing photon, we need to know angular resolution of the detector (EM Calorimeter). We have studied angular resolution using full-simulator (Jupiter) ECAL In this study, we have used single-gamma coming from IP to evaluate angular resolution.

4. GLD Detector Geometry in Jupiter • GLD detector has large-radius and fine-segmented Calorimeter. Calorimeter cell size and absorber material can be changed. It’s important to optimize Cost vs. Physics Performance. ECAL geometry in Jupiter ： R [m] Z [m] Structure W/Scinti./gap3/2/1(mm) x 33 layers cell size 1x1(cm2) barrel endcap 2.1-2.3 0.4-2.3 0-2.8 2.8-3.0 ECAL

5. Method of Gamma Reconstruction • Clustering • Find an energy-weighted central point of each layer • Fit each point with least-square method • Evaluate an angle between gamma-line and reconstructed gamma Calorimeter γ IP (generated point) reconstructed gamma

6. Angular Resolution Study ~ Position Resolution of Cluster ~

7. θ（φ）resolution [rad] = θ（φ）meas – θ（φ）MC Method (position resolution study of aaaaaaa isolated gamma cluster) • Generate single-gamma from IP with random direction • Clustering (more details in next page) • Search energy-weighted central point of cluster • Evaluate θ, φ of a central point • Compare with MC truth ECAL central point (θ,φ) IP (generated point) γ clustering

8. Clustering Method • Find the highest energy deposit cell • Make a cone around the cell • Define cells which are inside of the cone as one cluster (around all layers) • Find energy-weighted central point highest energy deposit cell central point clustering angle = 10° IP (generated point) γ@10GeV

9. Position Resolution of Cluster (cell : 1 cm) barrel endcap barrel endcap 1 GeV 2 GeV 5 GeV 10 GeV σ [mrad] σ [mrad] |cos(θ)| |cos(θ)| θ resolution is better for larger cos(θ) φ resolution is worse for larger cos(θ) ECAL geometrical effect Position resolution ： ~0.1 [cm] IP (generated point) gamma@10GeV

10. EnergyDependentResult of position resolution 1GeV 2GeV σ [mrad] σ [mrad] 5GeV 10GeV 1/√E 1/√E θ barrel： [mrad] φ barrel： [mrad] θ endcap： [mrad] φ endcap： [mrad]

11. Angular Resolution Study ~ Direction of Reconstructed gamma ~

12. Method (angular resolution study of reconstructed gamma) • Clustering • Find an energy-weighted central point of each layer • Fit each point with least-square method • Evaluate an angle between gamma-line and reconstructed gamma Calorimeter γ IP (shot point) reconstructed gamma

13. r d Histogram and Angular Resolution γ central point of cluster IP d r reconstructed gamma angle [rad] = r/d • r histogram F(r) fitting function σ = 48.3 ± 0.3 [mrad] gamma@10GeV

14. [mrad] Energy Dependence (1,2,5,10,50GeV) 1GeV 2GeV σ [mrad] Average over full acceptance 10GeV 5GeV 50GeV 1/√E

15. IP ECAL Shoot from another point gamma@10GeV • Shoot from x=y=20cm, z=0 reconstructed gamma • Shoot from IP IP ECAL σ= 48.3±0.3[mrad] σ= 48.6±0.3[mrad] If gamma has been shot from another position, we could not observe significant difference.

16. Calorimeter Component Dependence

17. Structure (cell size dependence) gamma : E = 10GeV 33 layers How about cell size dependence?

18. Cell size dependence 1 [cm] ： 48.3 ± 0.3 [mrad] 0.5 [cm] ： 46.4 ± 0.3 [mrad] <5% gamma @10GeV We could not observe significant improvement from 1cm to 0.5cm

19. Structure (energy dependence) gamma : E = 1~10GeV 33 layers How about energy dependence between 1cm and 0.5cm?

20. Energy Dependence (1,2,5,10GeV) 1GeV 2GeV 5GeV 10GeV No significant difference has been observed between 1cm and 0.5cm around all of energy.

21. Structure (Absorber dependence) gamma : E = 10GeV 33 layers How about absorber dependence?

22. Absorber Dependence (Tungsten, Lead) Tungsten[3mm] Lead[4.8mm] Same total radiation length Lead[3mm] Tungsten [3mm] ： 48.3 ± 0.3 [mrad] Lead [4.8mm] ： 45.5 ± 0.3 [mrad] @1x1 [cm] Angular resolution with Lead is better than Tungsten

23. Hit Distribution reconstructed gamma Angular resolution is better than Tungsten, since shower length is longer in Lead gamma MC depth gamma MC reconstructed gamma depth

24. Summary • Angular resolution of default-GLD Calorimeter (W:1cm) • The angular resolution is estimated to be 125mrad/√(E/GeV) • Dependence on cell size granularity and material dependence (W, Pb) has been studied • No significant difference has been observed between 1cm and 0.5cm • Lead is better than Tungsten for isolated gamma • Energy resolution is same • How about energy resolution for jet ? Next speaker T.Yoshioka

25. Backup

26. Fitting method Find a central point of each layer by energy weighted mean Fitting 2-dimentions (x-y) y y’ x Fitting new 2-dimentions (y’-z) weighted by energy deposit z y’ Distance[cm]

27. Hitting distribution and Average

28. Hit Distribution reconstructed gamma gamma MC gamma MC reconstructed gamma depth depth Angular resolution is better than Tungsten, since Lead has geometrical deeper distribution.