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Electromagnetic Showers with the MST Algorithm
Niels Meyer
The University of IowaMatthew Charles, Wolfgang Mader, Usha Mallik
ILC Workshop, Snowmass
August 17, 2005
● The MST algorithm● Classifying photons
● Status on efficiency & purity
The Minimum Spanning Tree Algorithm
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 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)
The Minimum Spanning Tree Algorithm
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 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 GeVuse 3D distancethreshold = 0.75cm
Finding Photons – Optimizing the MST
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 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
MST Output
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 5
MST Output
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 6
Identify Photons
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 7
● Look at cluster properties, try to find simple cutsGoal: keep it simple for now!
SizeContentShapePosition
Identify Photons
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 8
● Look at cluster properties, try to find simple cuts
SizeContentShapePosition
Identify Photons
Niels Meyer ILC Workshow, Snowmass August 17, 2005Page 9
● Look at cluster properties, try to find simple cuts
SizeContentShapePosition
Identify Photons
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 10
● Look at cluster properties, try to find simple cuts
SizeContentShapePosition
Identify Photons
● Look at cluster properties, try to find simple cuts
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 11
SizeContentShapePosition
Performance – Single Particles
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 12
● Photon efficiency:
● Accepts 5% pions, 10% neutrons, 10% K0L
98%
mean: 97%
First Look at Overlap
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 13
● Life is always easy with single particles● Try pi0 (two close-by photons)
First Look on Overlap
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 14
● Life is always easy with single particles● Try pi0 (two close-by photons)
First Look on Overlap
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 15
● High energy efficiency is simple with single particles● Try pi0 (two close by photons)
First Look on Overlap
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 16
● High energy efficiency is simple with single particles● Try pi0 (two close by photons)
Test: Tighter Threshold
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 17
● Try threshold=0.75cm (continuous cluster)
Test: Tighter Threshold
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 18
● Try threshold=0.75cm (continuous cluster)
Test: Tighter Threshold
Niels Meyer ILC Workshow, Snowmass August 17, 2005 Page 19
● Try threshold=0.75cm (continuous cluster)
Find ways to pick up more hits -
but now photoncores are known
Summary and Outlook
Niels Meyer ILC 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'
