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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