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+ e-e- Z0Z0 -- ~ χ0χ0 ++ ~ ++ χ0χ0 LC (hep-ph/ )

International Linear Collider (ILC) √s [GeV]500 Charge per bunch, N2x10 10 Beam size,  x [nm] 655 Beam size,  y [nm] 5.7 Bunch length,  z [  m] 300 Luminosity, L [cm -2 s -1 ]2x10 34 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 /E jet ≈ 30%/√E B = 4 T

Beamstrahlung at ILC N = 2x10 10 ;  x = 655 nm;  y = 5.7 nm n  = 1.26 (ILC) TESLA; z = 365 cm B = 4 T Per bunch 500 GeV: TESLA22 TeV 20 mrad crossing angle design 66 TeV ~20 mrad ~1 mrad

Very Forward Region of the LDC Detector hermeticity Luminosity measurements (LumiCal) Fast Beam diagnostics (BeamCal)

LumiCal and luminosity measurements Luminosity accuracy goal  L/L ~ 2x10 -4 if  min = 30 mrad  max = 75 mrad 1 year: ~10 9 events (  L/L) stat ~ 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 ( ) mrad σ ~ 10 2 fb (SPS1a) σ ~ 10 6 fb -- e+e+ e-e- Z0Z0 -- ~ χ0χ0 ++ ~ ++ χ0χ0 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

SiliconDiamond Band gap [eV] Resistivity, W×cm2.3× Breakdown field, V/cm3× Dielectric constant Energy/(e - -h pair), eV3.613 Average e - -h number per 100 mm (for MIP) Mobility, cm 2 /(V×s) e-e- 1350up to 4500 h480up 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 + -> R M ~ 1 cm diamond sensor cell size ~ 0.5 cm

Simulation Studies of the calorimeter performance Event – 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 GeV for the chosen parameters In 10% of bunch crossing a “high” energy e - occurs BG fluctuations The reconstruction is not ideal pure BG E> 20 GeV pure BG after reco

Simulation studies: energy resolution intrinsic  /E=22%/√E with BG (example)

Requirements from the simulation studies: Dynamic range – MIP/cm 2 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 mm 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 V 0 < |F| < ~2 V/  m Shielded box Light tight N 2 flow Sensor tests: Current-Voltage characteristics + open circuit measurements: |I| < 0.05 pA for 0 < |V| < 500 V Diamond Keithley 487 HV N2N2

Sensor tests: Current-Voltage characteristics “ohmic” behaviour, “low” current “non-ohmic” behaviour, “high” current No correlation with group# (wafer, surface treatment) R ~ (  ) at F = 1 V/  m

Sensor tests: Charge Collection Distance (CCD) Polycrystalline material with large amount of charge traps Q induced < Q created  = Q induced /Q created CCD ≈  L L

Sensor tests: CCD measurements MIP: Q created /L= 36 e - /  m CCD = L x Q measured /Q created CCD[  m] = Q measured [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 test Hadronic beam, 3 & 5 GeV (CERN PS) Fast extraction mode ~ / ~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 PMT1, PMT2 Beam intensity “Relative Intensity” Beam intensity

Linearity test – particle flux estimation + absolute calibration for one of the runs 1 RI = (27.3±2.9) 10 3 MIP/cm 2 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 ~10 7 MIP/cm 2 The deviation is at the level of systematic errors of the fluence calibration E64 FAP2 Fraunhofer sampleElement Six sample y = p[0]x

diamond-tungsten sandwich design of the BeamCal is feasible For E e ~ √ s/2 an efficient detection is possible for most of  For lower E e :  > 15 mrad (  E /E) intr = 22%/√E;  E /E = f(BG)   ~ rad;  φ ~ rad - for low BG density Dynamic range MIP/cm 2 (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 10 7 MIP/cm 2 Conclusions -> Sensor studies -> Simulation studies

Reserve

Simulation studies: efficiency N gen = 500 N reco = 521 E = 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 

Raman spectroscopy Resolution ~ 1 cm -1 Result = S(diam)/S(graphite)*1000