electromagnetic showers with the mst algorithm niels meyer the university of iowa matthew charles,...
TRANSCRIPT
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'