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

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'