1

LumiCal Optimization and Design

Takashi Maruyama

SLAC

SiD Workshop, Boulder, September 18, 2008

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• Geometry– Location and angular acceptance– Centered on the outgoing beam or the solenoid axis– Beampipe

• Tungsten thickness and no. of layers– Default is ECAL 20 layers of 2.5 mm+10 layers of 5.0mm

• Segmentation• Electronics dynamic range

– MIP sensitivity– KPiX

• Occupancy– Bhabha event rate– Pairs, ee+had, ee– 4 buffer storage of KPiX

• Luminosity precision goal• LHCAL

– Do we need it?

LumiCal related issues

3

references

• Bill Morse: SiD LumiCal notes

• David Strom: all about luminosity measurement.

• FCAL collaboration

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Simulations• EGS

– Simple geometry– Study EM shower

characteristics• FLUKA

– Forward region geometry• LumiCal/BeamCal

centered on out beam

• Include Endcap Cal

– LumiCal simulation• OPAL r- segmentation

– Study angular resolution

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 0.5 1 1.5 2 2.5 3 3.5 4

250 GeV e- 30 ~ 50 layers of W + Si (0.032 cm) + G10 (0.068 cm) + Air (0.025 cm)

LumiCal BeamCal

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FLUKA Geometry

R=6 cm hole displaced by x=-158 cm * 0.007 and centered on out beam

LumiCalLHCAL

ECAL

LumiCal LHCAL

New Conical beampipe design

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LumiCal Z-location

• Move LumiCal ~10 cm w.r.t. EMCal

250 GeV e-EMCal

LumiCal

1 cm gap

Ene

rgy

Dep

ositi

on in

Si L

ayer

s (G

eV)

cos

LumiCalEMCal

BeamCal

0 cm

-5

-10

-15

-20

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Energy Deposition in Si Layers

• Energy containment

• 20 lyrs of 2.5mm + 10 lyrs of 5.0mm looks good.

• Shower max.– Layer #13 is shower max for

2.5 mm W

0.20

0.15

0.10

0.05

0.00

Ene

rgy

Dep

ositi

on in

Si L

ayer

(G

eV)

403020100

Si Layer

2.0 mm 2.5 mm 3.0 mm 3.5 mm 4.0 mm 2.5 mm (20 layers) +

5.0 mm (10 layers)

250 GeV e- normal incident

W Thickness (mm)

No Layers

2.0 50

2.5 40

3.0 35

3.5 30

4.0 25

~240 MeV/layer

W thickness

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Energy Resolution

• Energy resolution improves as W gets thinner.• As long as the energy containment is satisfied.• 20 lyrs of 2.5mm + 10 lyrs of 5.0mm yields an

optimum resolution for 30 layers.

2.5 mm W

Energy in Si Layers (MeV)

50 layers45403530

0.4

0.3

0.2

0.1

0.0

Ene

rgy

Res

olut

ion

4.03.53.02.52.0

W Thickness (mm)

50 layers 45 layers 40 layers 35 layers 30 layers

,

E / E = / E

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More on 20 lyrs (2.5mm)+10 lyrs (5.0mm)

• Energy resolution parameter is dependent on energy– 15%/E at low energy– 20%/ E at high energy

• Energy leakage is small even at 500 GeV.

1.4x10-3

1.2

1.0

0.8

0.6

0.4

0.2

0.0

De

po

site

d E

ne

rg

y /

Ein

2520151050

Layer

1 GeV 10 GeV 50 GeV 100 GeV 250 GeV 500 GeV

0.25

0.20

0.15

0.10

0.05

0.00

Energ

y R

eso

lutio

n

5004003002001000

Energy (GeV)

Good configuration for the LumiCalα

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Luminosity measurement

• Luminosity precision L / L:– 10-3 106 W+W- events in 5 years (500 fb-1)– 10-4 GigaZ

L/L=(Nrec - Ngen)/Ngen

– Bhabha d/d ~ 1/3

L/L~2 /min , is a systematic error.

must be less than ~20rad to reach L/L = 10-3.– Detector radial location must be know within 30m.

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LumiCal simulation• Segment Si layer equally

into r and N, perfect alignment and no dead space.

• Non-projective geometry– Same detector in depth-

wise

• Collect dE/dX in each channels.

• Output lyr, ir, iphi, edep.• Reconstruct rec and

compare with gen

OPAL Luminometer: 14 lyrs of 3.5mm + 4 lyrs of 7.0mm

OPAL achieved L/L = 3.4 10-4

R- segmentationr = 2.5 mm = 11.25 (=360/32)

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250 GeV Pseudo-Bhabha events

(mrad) (mrad)

E (

GeV

) 44 mrad 112 mrad

1/3

• Although good Bhabha generator is available, real Bhabha events obscure the angular resolusion issue.– Bhabhas need to be separated from radiative Bhabhas.– Shower finder needs to be optimized for different segmentation.

• Genetate 250 GeV e- with 1/3 distribution

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Angular resolution and bias

(rec)(gen) (mrad)

Wi = Log energy weight*

Max{0, const.+ln(Ei/Etot)}

i

ii

w

w Bias

=0.017 mrad

Resolution()=0.046 mrad

* Linear energy weight is much worse. Awes et al, NIM A311, 130 (1992)

r=2.5mm, N=32

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L/L vs. segmentation

r

(mm)

(mrad)

(mrad)

L/L

2.0 0.008 0.042 3.310-4

2.5 0.017 0.046 7.910-4

3.0 0.023 0.050 1.010-3

4.0 0.036 0.058 1.710-3

5.0 0.049 0.069 2.210-3

(mrad)

(mrad)

L/L

16 0.017 0.046 7.710-4

32 0.017 0.046 7.910-4

48 0.017 0.045 7.610-4

64 0.014 0.045 6.610-4

Radial segmentation

segmentation

N = 32

r = 2.5 mm

2.0x10-3

1.5

1.0

0.5

dL / L

5.04.54.03.53.02.52.0

Radial Segmentation (mm)

L / L < 10-3 can be reached by r < 3mm.

• Finer segmentation helps, but not much.

– Finer segmentation will help shower separation.

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Radial segmentation

• When misalignment and dead space are considered, r = 2 mm is probably required.– D. Strom: All biases in the radial coordinate must be

measured in a test beam and not calculated from Monte Carlo.

• A tracking detector like MAPS in front of the LumiCal– Precise polar angle measurement– Fine LumiCal segmentation is not necessary

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Max Energy Deposition in Si channel

• Max energy deposition– 160 MeV (7010 fC*)

• MIP– MPV~0.0925 MeV (4.1 fC)

• Bhabha ~ 1710 MIP• If we want S/N ~ 10 for MIP,

we need 17,000 dynamic range.– 2 gains + 10 bit ADC

Max Energy Deposition (MeV)

250 GeV e-

250 GeV -

Energy Deposition (MeV)

160 MeV

* 3.65 eV to generate e-h pair

KPiX (2 gains + 13 bits) can handle it.

r = 2.5mmN = 32

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Occupancy

• Bhabha event rate– Nev per BX @ILC 500 Nominal=

5.9 [1/2min – 1/2

max] ( in mrads)

– 7 ev/train for min=44 mrad, max=112 mrad

• Backgrounds– Pairs hadrons

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Pairs in LumiCal

1.5 e+/e- / BX hit LumiCal

282 BXs (10% train)R=6 cmANTI-DID

Pairs @ ILC 500 Nominal are confined within ~4 cm. However, there are pairs outside the ring of death, and >4000 e+/e-/train hit the LumiCal.

X (cm)

Y (

cm)

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Pair occupancy in LumiCal

• 1.5 e+/e- / BX reaching LumiCal

• Hits are mostly in the front ~10 layers.

• Inner most channels have more than 4 hits.

Hits per Train

r = 2.5 mm, N = 32

Inner most channels

KPiX has only 4 buffers.Need a new chip being developed for the BeamCal.

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Possible LumiCal design

• 6” wafer can be used if Rout < 20 cm

• 12 petals are all different; need different Masks.

• Non-projective geometry; same detector in depth-wise.

• Each petal is held by four alignment pins at the corners.

Oriunno

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LHCAL

• Original SiD did not have LHCAL.

• LDC introduced LHCAL.– Hermiticity– Veto capability of ee+had,

ee• The solid angle coverage

of LHCAL is miniscule, ~210-3.

• As long as the LumiCal has 100% MIP sensitivity, LHCAL is not needed.

LHCAL