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Tianchi Zhao

University of Washington

Concept of

an Active Absorber CalorimeterA Summary of LCRD 2006 Proposal

A Calorimeter Based on Scintillator and Cherenkov Radiator Plates Readout by SiPMs

Tianchi Zhao

University of Washington

Adam Para

Fermilab

March 12, 2006, LCWS06 Bangalore, India

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Energy Compensation

Reference:1. “Compensating hadron calorimeters with Cerenkov light” Winn, D.R. Worstell, W.A. , IEEE Trans. NS Vol 36 (1989) 334 2. “Hadron Detection with a Dual-Readout Calorimeter” N. Akchurina et al., NIM A 537 (2005) 537-5613. “Cherenkov Compensated Calorimetry”, Yasar Onel et al., 2004 LCRD Proposal

factorn compesatio : 1

sc

chsch E

EEE

Hadron energy Eh is given by:

Eh : Compensated hadron energy

Esc : Energy measured by plastic scintillators

Ech : Energy measured by cherenkov radiators

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Basic Idea of Active Absorber CalorimeterIn a sampling calorimeter based on active detector (scintillator)

+ absorber layers, partially replace absorber plates by cherenkov radiator and

read out both scintillation light and cherenkov light.• Thin plastic scintillator plates: Measure energy of both hadron and EM components of

hadron showers as in a standard sampling calorimeter

Cherenkov radiator

Plastic scintillator

Heavy structural layer

• Thick Cherenkov radiator plates: Measure mostly energies of EM components in hadron

showers in an active absorber calorimeter

• Both readout by WLS fiber and SiPM/MPPC

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Configuration Example Consider a 40 layer arrangement

Material LayersT

(cm)

Layer Thickness

(cm)No. of T

Plastic scintillator 40 80 40 0.5 = 20 0.25

Lead glass 30 30 30 2 = 60 2

Iron 30 16.8 30 0.5 = 15 0.89

Iron 10 16.8 10 2.5 = 25 1.49

TOTAL 40 120 4.63

20 mm lead glass

5 mm steel

~1.3 X0 25 mm steel

Last 10 layersFirst 30 layers 5 mm plastic scintillator

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Options for EM Calorimeter Section

15 mm PbF2

3 mm scintillator

2 mm tungsten

15 mm PbF2

3 mm scintillator

2 mm tungsten

20 layers

• Good EM energy resolution• Maintaining energy compensation

1. Any other EM calorimeter considered for ILC 2. A segmented active absorber calorimeter with dual energy readout

Example

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Transverse Segmetation

• Need Monte Carlo simulation to optimize the choice of segmentation for - EM section - Front part of hadron section - Back part of hadron section

• Minimum size of plates mainly limited cost considerations 3 cm × 3 cm (?)

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Number of p.e. measured by using cosmic ray muons

Lead glass: 2.4 0.5 p.e.

Bicron 408: 27 4 p.e. Ralph Dollan, 2004 Thesis

Cherenkov Light Readout by WLS Fiber

• Groove along 40 mm length

• White paper wrapped

• 1 mm BCF-91AWSL fiber

• One end open

• XP1911 PMT

(Average Q.E. ~ 13% for BCF-91A )

Bicron 408

6 x 6 x 30 mm3

P.E. yield of lead glass is about 5% of plastic scintillator

Lead glass SF57

10 x 10 x 40 mm3

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Cherenkov Light Yield of 1 Charged Particles

Forward

Cherenkov Radiator Density X0

(cm)

(cm)

Index of refractio

n

Absorption Edge (nm)

SF2 lead glass 3.85 2.76 38 1.65 330

SF6 lead glass 5.2 1.7 30 1.81 360

SF57 lead glass 5.5 1.5 28 1.85 370

PbF2 crystal 7.8 0.93 20 1.82 250

UVT acrylic 1 40 80 1.5 250• Lead glass was popular calorimeter material in LEP experiments

• Cast or extruded lead glass has the same light yield as cut/polished crystals

Plastic scintillator light yield

~ 10,000 photons/cm

Chrenkov light yield:

200 – 300 photons/cm

Isotropic

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Cherenkov Plate Readout by MPPC or SiPM

MPPC or SiPM WLS fiber

Cherenkov Radiator

2 cm

Target: Combined efficiency = η1 × η2 × η3 × η4 >1%

• η1 : probability of a photon hitting the core of a WLS fiber

• η2 : conversion efficiency of WLS fiber

• η3 : light trapping efficiency in WLS fiber

• η4 : MPPC/SiPM quantum efficiency

Cherenkov photon Photoelectrons

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Signals from a 1 Charged Particle

Number of P.E. = N0 x η1 x η2 x η3 x η4 = 400 x 1.6 % = 6.4

• Cherenkov light yield: N0 = 400 ’s in 2cm radiator

• Light collection efficiency by WLS fiber: η1 ~ 50%

• WLS fiber efficiency: η2 ~ 80%

• Assume η3 ~ 10% with mirror at far end of fiber

• MPPC Q.E.: η4 ~ 40 % (100 pixel device may be sufficient)

MPPCMirro

r

WLS fiber: high efficiency for blue light; emits green/yellow light to match MPPS

WLS fiber

Should be able to make reasonable measurements for high energy EM showers

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Basic structure

An Alternative Configuration

Material LayersT

(cm)

Layer Thickness

(cm)

No. of

T

Plastic scintillator 40 80 40 0.5 = 20 0.25

UVT Lucite 30 70.3 30 2 = 60 0.85

Uranium 30 10.5 30 0.5 = 15 1.43

Iron 10 16.8 10 2.5 = 25 1.49

TOTAL 40 30 120 4.02

20 mm lucite

5 mm uranium

25 mm steel

Last 10 layersFirst 30 layers

5 mm plastic scintillator

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Potential Advantages• Energy compensation for hadron showers on event by event basis

as demonstrated by the DREAM Project, but allowing for fine transverse and longitudinal segmentation

• Performance should be better than the dual r eadout calorimeter of Dream project since cherenkov radiator in our implementation is 2/3 of total volume!!

• Energy resolution should be better than a calorimeter based only on scintillator plates and should achieve the “required” jet energy resolution

• Tighter spatial spread of hadron showers recorded by Cherenkov radiator may help correctly assigning energy clusters in HCal to tracks that produced them, therefore, improving the results of PFA.

• Very flexible design options for material choices and segmentations

E/%30

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Disadvantages

• Significant cost increase compared to HCal that uses plastic scintillator plates only

• Density of calorimeter is reduced compared to a design that uses passive absorber only. Using a heavy metal such as uranium or tungsten may solve this problem.