Design Studies and Sensor Test for the Beam Calorimeter of the ILC Detector

E. Kuznetsova DESY Zeuthen

a facility for precision measurements

International Linear Collider (ILC) – why?e+e- √s = 500 GeV in ~2015

H f (Z, W-)

f (Z, W+)

-

e+

e-

Z0

-

~

χ0

+~ +

χ0

LC

(hep-ph/0510088)

International Linear Collider (ILC)

√s [GeV] 500

Charge per bunch, N 2x1010

Beam size, x [nm] 655

Beam size, y [nm] 5.7

Bunch length, z [m] 300

Luminosity, L [cm-2s-1] 2x1034

Nominal parameters (Aug.2005)e+e-, e-e- (e, )

90 GeV ≤ √s ≤ 500 GeV (1 TeV)

polarized beams

2-20 mrad crossing angle

ILC Detector - Large Detector Concept (LDC)

“Particle flow method” (PFLOW) : TPC + calorimetry

Ejet/Ejet ≈ 30%/√E

B = 4 T

Beamstrahlung at ILCN = 2x1010; x = 655 nm; y = 5.7

nm

n = 1.26 (ILC)

TESLA; z = 365 cm

B = 4 T

Per bunch crossing @ 500 GeV:

TESLA 22 TeV20 mrad crossing angle design

66 TeV

~20 mrad

~1 mrad

Very Forward Region of the LDC

Detector hermeticityLuminosity measurements (LumiCal)Fast Beam diagnostics (BeamCal)

LumiCal and luminosity measurementsLuminosity accuracy goal L/L ~ 2x10-4

3

1

d

d

dd

dL

dt

dNmax

min

if min = 30 mradmax = 75 mrad

1 year:~109 events (L/L)stat ~ 10-4

Cross section calculation

polar angle measurements

~ 2()sys/

(L/L)sys

Si/W calorimeter(26-141) mrad

BeamCal: motivation

Beam diagnostics:

Low angle detection:

ILC; z = 355 cm

+ vertical offset of 10nm

(5.6-26.6) mrad

σ ~ 102 fb (SPS1a) σ ~ 106 fb

-

e+

e-

Z0

-

~

χ0

+

~ +

χ0 e+

e-

e+

e-

+

-

BeamCal: requirements

Diamond-Tungsten sandwich calorimeter

•High radiation hardness (up to 10 MGy/year)•Small Moliere radius and high granularity•Wide dynamic range

 Silicon Diamond

Band gap [eV] 1.12 5.47

Resistivity, W×cm 2.3×105 1013-1016

Breakdown field, V/cm 3×105 107

Dielectric constant 11.9 5.7

Energy/(e--h pair), eV 3.6 13

Average e--h number per 100 mm (for MIP) 9200 3600

Mobility, cm2/(V×s)

e- 1350 up to 4500

h 480 up to 3800

T.Behnke et al., 2001

Why diamond?

•Resistant enough to e/m radiation (at least for low energy)

•Comparison with silicon:

Simulation studies of the calorimeter performance•TESLA Detector design

Z - segmentation :

tungsten 3.5 mm Layer = = 1 X0

diamond 0.5 mm

(r,) - segmentation :

tungsten absorber + -> RM ~ 1 cm

diamond sensor

cell size ~ 0.5 cm

Simulation Studies of the calorimeter performanceEvent – 50-250 GeV e-

Background – pairs from 1 bunch crossing (“Guinea-Pig”)Full detector simulation – BRAHMS (GEANT3)

Statistics: 500 bunch crossings

Simulation studies: efficiency

Simulation studies: fake rate

~2% of “fake” e- of E > 50 GeVfor the chosen parameters

• In 10% of bunch crossing a “high” energy e- occurs• BG fluctuations • The reconstruction is not ideal

pure BGE> 20 GeV

pure BGafter reco

Simulation studies: energy resolutionintrinsic /E=22%/√E

with BG (example)

Requirements from the simulation studies:• Dynamic range – 10-105 MIP/cm2

• Digitization - 10 bit (considered segmentation)

Sensor tests: pCVD diamonds

Polycrystalline Chemical Vapour Deposition Diamonds

Typical growth rate : ( 0.1 – 10 ) m/hr

Si

•Defects at the grain boundaries•Graphite phase presence•Si, N impurities

substrate side

growth side

Sensor tests: samples

Requirements:- stability under irradiation- linearity of response

Samples:Fraunhofer IAF, Element

Six

First step - Fraunhofer IAF (Freiburg) :

• CVD diamond 12 x 12 mm2

• 300 and 200 m thickness• Different wafers and different surface treatment (3 samples/group):

•#1 – substrate side polished; 300 m•#2 – substrate removed; 200 m•#3 – growth side polished; 300 m•#4 – both sides polished; 300 m

0 < |V| < 500 V0 < |F| < ~2 V/m

Shielded box•Light tight•N2 flow

Sensor tests: Current-Voltage characteristics

+ open circuit measurements: |I| < 0.05 pA for 0 < |V| < 500 V

Dia

mo

nd

Ke

ith

ley

48

7

HV

N2

Sensor tests: Current-Voltage characteristics

“ohmic” behaviour, “low” current

“non-ohmic” behaviour, “high” current

No correlation with group# (wafer, surface treatment)R ~ (1011-1014 ) at F = 1 V/m

Sensor tests: Charge Collection Distance (CCD)

Polycrystalline material with large amount of charge traps

Qinduced < Qcreated

= Qinduced/Qcreated

CCD ≈ L

L

Sensor tests: CCD measurementsMIP:

Qcreated/L= 36 e-/m

CCD = L x Qmeasured/Qcreated

CCD[m] = Qmeasured[e-]/36

CCD range = f(wafer), but no correlation with surface treatment

Fast measurements - in 2 minutes after the voltage applied…

Sensor tests: CCD vs dose

Group#2 (wafer#2, cut substrate) Group#3 (wafer#3, untreated substrate)

F = 1 V/m

Group#3 (wafer#3, untreated substrate)

Sensor tests: more samples!Fraunhofer sample Element Six

I < 0.3 nA

• Stabilizes after ~20 Gy!• CCD ~ 30 m• dose rate influence…

Sensor tests: linearity testHadronic beam, 3 & 5 GeV (CERN PS)Fast extraction mode

~104-107 / ~10 ns

ADC

Diamond Scint.+PMT&

signal gate

10 ns

17 s

Linearity test – relative intensity measurements

+ offline PMTs calibration

+ absolute intensity measurement (Thermoluminescence dosimetry)

wide intensity range

PM

T1,

PM

T2

Beam intensity

“Rel

ativ

e In

ten

sity

”

Beam intensity

Linearity test – particle flux estimation

+ absolute calibration for one of the runs

1 RI = (27.3±2.9) 103 MIP/cm2

Linearity of the corrected PMT response(at a reduced range)

Linearity of the diamond response

30% deviation from a linear response for a particle fluence up to ~107 MIP/cm2

The deviation is at the level of systematic errors of the fluence calibration

E64 FAP2

Fraunhofer sampleElement Six sampley = p[0]x

•diamond-tungsten sandwich design of the BeamCal is feasible•For Ee~ √s/2 an efficient detection is possible for most of • For lower Ee: > 15 mrad • (E/E)intr = 22%/√E; E/E = f(BG)• ~ 10-4 rad; φ ~ 10-2 rad - for low BG density• Dynamic range 10-105 MIP/cm2 (TESLA)

• pCVD diamond – a promising sensor material• A set of measurements is established to test the sensor quality• A feedback to Fraunhofer IAF allows to improve quality• We already have samples

• with CCD of ~30 m• with a stable response• with a ~linear response for a fluence up to 107 MIP/cm2

Conclusions

-> Sensor studies

-> Simulation studies

Reserve

Simulation studies: efficiency

Ngen = 500Nreco = 521E = 100 GeV

Simulation studies: energy resolution

Simulation studies: angular resolution

Simulations:Sr + diamond

CCD – irradiation studies – results

Group #1 (substrate side polished). HV = 300V

Group #2 (substrate side removed). HV = 200V

CCD – irradiation studies – results

Group #3 (growth side polished). HV = 300V

Group #4 (both sides polished). HV = 300V

Linearity test – PMT calibration

),(),(),(

),(),(

)tan(,

1)(

202

0

2200

2/12

HVQdHVQdd

dHVQ

ddHVQddHVQ

Rd

Dd

ddI

PMT

LED

Raman spectroscopy

Resolution ~ 1 cm-1

Result = S(diam)/S(graphite)*1000