1. Electromagnetic Showers with the MST Algorithm Niels Meyer The University of Iowa Matthew Charles, Wolfgang Mader, Usha Mallik ILC Workshop, Snowmass August 17, 2005 ● The MST algorithm ● Classifying photons ● Status on efficiency & purity

2. The Minimum Spanning Tree Algorithm Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 2 ● Recursive algorithm ● Any two hits with distance below a threshold end up in the same cluster ● User has to define distance definition and a threshold Implementation for hep.lcd available in CVS (Matthew Charles, Wolfgang Mader, N.M.) More details: “Calorimeter algorithms” sessions (Friday afternoon / Saturday morning)

3. The Minimum Spanning Tree Algorithm Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 3 ● Recursive algorithm ● Any two hits with distance below a threshold end up in the same cluster ● User has to define distance definition and a threshold Example: pion with ~4 GeV use 3D distance threshold = 0.75cm

4. Finding Photons – Optimizing the MST Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 4 ● Let's start simple, use 3D distance (no energy, angle,...) Control sample: single particles (~1000 each) 1-10GeV in ECal barrel, SDFeb05 detector ● Find MIP tracks first, don't use these hits ● Optimize threshold by energy collected 2cm threshold ~97% energy 1 2 3 cm Energy fraction picked up

5. MST Output Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 5

6. MST Output Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 6

7. Identify Photons Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 7 ● Look at cluster properties, try to find simple cuts Goal: keep it simple for now! Size Content Shape Position

8. Identify Photons Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 8 ● Look at cluster properties, try to find simple cuts Size Content Shape Position

9. Identify Photons Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 9 ● Look at cluster properties, try to find simple cuts Size Content Shape Position

10. Identify Photons Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 10 ● Look at cluster properties, try to find simple cuts Size Content Shape Position

11. Identify Photons ● Look at cluster properties, try to find simple cuts Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 11 Size Content Shape Position

12. Performance – Single Particles Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 12 ● Photon efficiency: ● Accepts 5% pions, 10% neutrons, 10% K 0 L 98% mean: 97%

13. First Look at Overlap Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 13 ● Life is always easy with single particles ● Try pi0 (two close-by photons)

14. First Look on Overlap Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 14 ● Life is always easy with single particles ● Try pi0 (two close-by photons)

15. First Look on Overlap Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 15 ● High energy efficiency is simple with single particles ● Try pi0 (two close by photons)

16. First Look on Overlap Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 16 ● High energy efficiency is simple with single particles ● Try pi0 (two close by photons)

17. Test: Tighter Threshold Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 17 ● Try threshold=0.75cm (continuous cluster)

18. Test: Tighter Threshold Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 18 ● Try threshold=0.75cm (continuous cluster)

19. Test: Tighter Threshold Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 19 ● Try threshold=0.75cm (continuous cluster) Find ways to pick up more hits - but now photon cores are known

20. Summary and Outlook Niels MeyerILC Workshow, Snowmass August 17, 2005 Page 20 ● Use MST algorithm to find electromagnetic showers ● Promising results on single particles and pi0 ● Work in progress: ● Stay tuned... Optimize energy collection efficiency Find criteria for low-E photons Study overlap with pions, neutral hadrons... Put together a 'photon finder'