analog vs. digital hadron calorimetry for the...

Analog vs. DigitalAnalog vs. DigitalHadronHadron CalorimetryCalorimetry

for the ILCfor the ILCDhiman Chakraborty

for the NIU/NICADD ILC detector group

International Linear ColliderLarge Detector Meeting

LLR, Paris, January 13-15, 2005

ILC LD meeting, 14-01-2005

Analog vs. Digital HCal for ILC Dhiman Chakraborty 2

IntroductionIntroduction

We consider a hadronic calorimeter with a few thresholds (1-3).Compare gas and scintillator as live media:

Single particle energy resolution,Shower width,Clustering.

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Geometries ConsideredGeometries Considered

Scint HCal

Steel 20mmPolystyrene 5mm

Gas Geom1

Steel 20mm

Gas 5mm

Gas Geom2

G10

Glass 1mm

Gas 1mm

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Number of cells hit by Number of cells hit by ππ++s of s of 2, 5, 10, 20, 30, 50 GeV2, 5, 10, 20, 30, 50 GeV

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ππ++ energy resolution as function of energy resolution as function of energy for different (linear) cell sizesenergy for different (linear) cell sizes

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EEnergy resolution for 10 GeV nergy resolution for 10 GeV ππ++ss

σ/E=0.183 σ/N=0.166

9cm2 cells

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EEnergy resolution for 50 GeV nergy resolution for 50 GeV ππ++ss

σ/E=0.101 σ/N=0.153

9cm2 cells

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Nhit Nhit correlations for different correlations for different cell energy thresholdscell energy thresholds

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Nhit correlations for different cell Nhit correlations for different cell energy thresholdsenergy thresholds

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Nhit correlations for different cell Nhit correlations for different cell energy thresholdsenergy thresholds

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Alternatively,Alternatively,

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CompensationCompensation

Cell counting has its own version of the compensation problem (in scintillators).With multiple threshold this can be overcome by weighting cells differently (according to the threshold they passed).In MC, 3 thresholds seem to be adequate

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After semiAfter semi--digital treatmentdigital treatment

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Energy resolution:Energy resolution: 5050 GeV GeV ππ++ss

σ/E=0.101 σ/E=0.092

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Energy resolution: 10 GeV Energy resolution: 10 GeV ππ++ss

σ/E=0.183 σ/N=0.164

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ππ++ energy resolution vs. energyenergy resolution vs. energy

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Time of flightTime of flight

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ToF dependenceToF dependence

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CrossCross--talktalk(10% of cell E leaks equally to 4 neighbors)

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Nhit vs. fraction of Nhit vs. fraction of ππ++ E in cells with E>10 MIP:E in cells with E>10 MIP:1cm1cm x 1cm x 1cm scintillator cellsscintillator cells

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Nhit vs. fraction of Nhit vs. fraction of ππ++ E in cells with E>10 MIP:E in cells with E>10 MIP:GasGas vs. scintillatorvs. scintillator

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ππ++ energy resolution vs. energyenergy resolution vs. energyM

ultip

le th

resh

olds

not

use

d

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NonNon--linearitylinearityNhit/GeV varies with energy.This will introduce additional pressure on the “constant” term.For scintillator the non-linearity can be effectively removed by “semi-digital” treatment.

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Density of hitsDensity of hits

Need a hierarchy in the absence of an energy measurementLocal density of hits is an obvious candidate. A simple-minded density variable:

di = Σ (1/Rij),where Rij is the angular distance between cells i & j.

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Position resolutionPosition resolutionM

easu

red

rela

tive

to th

e en

ergy

wei

ghte

d re

solu

tions

unweighted

Density weightedEnergy weighted

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Density vs. Density vs. EnergyEnergy

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WidthWidthFind centroid {Σwixi/Σwi}‘width’ = sqrt(ΣwiR2

i/Σwi)Three weights were used:

Unweighted (wi=1)

Energy weighted (wi=Ei)

Density weighted (wi=nearest-neighbor occupancy in a 5x5 window in lyrs k-1,k,k+1)

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Distance to Distance to farthestfarthest cellcell

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Density Density of farthestof farthest cellcell

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Distance to farthest cellDistance to farthest cell

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Density of farthest cellDensity of farthest cell

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BackscatterBackscatter

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Shower Shower widthwidth for 10GeVfor 10GeV ππ±±

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Shower width for 50GeVShower width for 50GeV ππ±±

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π± angular widthrms shown as bars

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ππ±± angular width: energy weightedangular width: energy weighted

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ππ±± angular width: density weightedangular width: density weighted

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CommentsCommentsThere is no clear cut case either way at the moment; detailed studies of assessing impact needed.Will look at cluster separability next.Need to evaluate this in the global context of calorimeter performance.

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ClusteringClusteringClustering based on local densityworks well.It is an alternative to track-seeded clustering.Can be used in the ECal and HCal.Full PFlow implementation givesencouraging results.

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10 GeV10 GeV ππ0 0 →→ γγγγD

ensi

ty w

eigh

ted

θ−φ

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ΣΣ++ →→ ppππ0 0 →→ ppγγγγ

p

π0

Den

sity

wei

ghte

dθ−

φ

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SummarySummaryLarge parameter space in the nbit-segmentation-medium plane for hadron calorimetry. Optimization through cost-benefit analysis?Scintillator and Gas-based ‘digital’ HCalsbehave differently.Need to simulate detector effects (noise, x-talk, non-linearities, etc.)Need verification in test-beam data.More studies underway.