Introduction Test results standard tests Test results extended tests Conclusions

Transcription

1 Production and Tests of Hybrid Photon Detectors for the LHCb RICH Detectors, University of Edinburgh On behalf of the LHCb experiment Introduction Test results standard tests Test results extended tests Conclusions LHCb RICH1 RICH2

2 LHCb RICH RICH1 side view RICH = Ring Imaging CHerenkov detector 3 radiator media aerogel, C 4F 1,, CF 4 cos(θ ) c = 1 n v c RICH2 Flat mirrors Spherical Mirrors Support Structure spherical mirrors focusing ring image tilt outside acceptance secondary flat mirrors magnetic shielding 7.2 m acceptance RICH1: 25-3mrad RICH2 :15-12mrad 12mrad Central Tube Photon Funnel + Shielding 2

3 RICH Photondetector Requirements 6 4 RICH1 1 6 RICH 2 4 RICH2 2 2 y (c cm) y (c cm) -2-2 C 4 F 1 (small) -4 Aerogel (large) x (cm) x (cm) single event ent in the full GEANT3 based simulation used in performance studies photodetector area: 2.6 m 2 active area fraction: 65% single photon sensitivity: 2-6 nm # of electronic channels: 5k quantum efficiency: >2% LHCb DAQ rate: 4MHz good granularity: 2.5 x 2.5 mm 2 rad. tolerant: 3kRad/year CF 4 answer: 484 3

4 Specifications Anode Photon detector: Quartz window, S2 photocathode Typical QE de >.7eV Cross-focussing optics (tetrode structure): De-magnification by ~5 Active diameter 72mm 484 tubes for overall RICH system 2 kv operating voltage (~5 e [eq. Si]) Vacuum photon detector Anode: pixel Si-sensor array ( Alice mode ) small pixels low noise bump-bonded to binary readout chip assembly encapsulated in vacuum tube LHCb readout mode : 8-fold binary OR effective pixel array pixel size 5μm 5μm sufficient 4

5 Photon Detector Test Facilities Photon Detector Test Facilities (PDTF): (Edinburgh & Glasgow) 2 test stations per site design test rate: 1 / day / site standard preparation and test programme per : ~6hrs extended tests: on ~1% of s Quantum Efficiency (Edinburgh) Backpulse Signal (Glasgow) Storage: under He-free atmosphere: N 2 gas flow (.2 l/min) PDTF station Dark box flat & pointing light source Electronics & Power supplies DAQ PC 5

6 Testing Programme 6

7 Classification System guideline for usability in RICH: 161x class A+ : exceed specifications significantly 282x class A : clear pass in all aspects 6x class B : may fail specs, but recommended for usage s with slightly increased dark count 42x class E : flagged with an issue, still usable in RICH s with increased LC or 1 5% dead pixels 12x class F : clear fail reject 12 failed s: 9x replaced with good 3x accepted as failure within LHCb responsibility misc: 4x repaired, retested and accepted as good 2x anode problem, but usable, under study, not classified pass: of 559 > 97.8% fail: 12 of 559 < 2.2% 282 category 6 A+ A B E F

8 Mechanical Tests t 555 passed 2 failed on first test leaned by ~.4mm tubes repaired to pass as well point of first possible contact PDTF: mechanical test jig : 83.mm +.mm -.1mm Teflon tape:.1mm Jig : 83.4mm gap:.1mm any contact = failure 8

9 Pixel Chip Threshold and Noise excellent signal over noise: specification <measured> average signal 2kV: C = 5 e - average threshold: T = < 2 e e - average electronic noise: N = < 25 e e - signal over noise: S/N = (C-T)/N > (min, max) = (21,33) 16 global threshold setting 16 electonic noise of pixel chip 14 signal-over-noise of pixel chip <threshold>: 12 <noise>: <S/N>: e e threshold [e-] noise [e-] S/N

10 Anode Channel Yields very good yields for response of individual pixels: in Alice mode 8192 pixels / <dead pixels>: 12.4 pixels / <poor pixels>: 1.6 pixels / dead pixels per <dead pixels>: 12.4 pixels signal response < 5% <noisy pixels>: 2.1 pixels / need masking pixels noisy pixels per 45 poor pixels per <noisy ypixels>: 2.1 pixels <poor pixels>: 1.6 pixels pixels pixels bias of averages 1

11 Anode Leakage Current goal: typical value of: LC ~ 1μA achieved for all bare chips when unpowered with bias of 8V in : bad heat dissipation anode heat up by ~12-15 C increase in leakage current: ~*2 for 6 C found two classes: low 8V (<1μA): quadratic behaviour up to 9V bias medium 8V (~1μA 3μA): turn up point between: 4 6V Bias Curre ent [arbitrary units] IV scans for sample of s normalised Bias Voltage [V] Anode Leakage Current: at 8V bias class E & F ((corresponds to two sensor batches)) Leakage Current [μa] 11

12 . Imaging g pulsed LED run (2k events, ~3 npe/event) fit of sensor position batch 1-7 batch 8-25 Distribution of image centres cylindrical reflection: reflection on Al coating -5 fit of image diameter linear demagnification Deviation from centre of chip [μm] Y circles: LHCb pixel Ø -15 X Deviation from centre of chip [μm] sensor displacement: due to positioning error linear demagnification: <D> = x >1mm (2 LHCb pixel): signal loss possible in magnetic field linear demagnification 12

13 Photoelectron Response HV scan: look for photon yield onset of response onset of charge sharing between pixels slope due to increasing efficiency for back-scattered e- Dark Count settling: typical decay: factor 2 in 3min after initial ramp-up time constants vary 13

14 Anode Response Bias Voltage Scan Bias voltage scan: look for photon yield very sensitive to timing: onset of response charge signal vs. strobe pulse bias of full depletion drift time in sensor bias V plateau of over-depletion >5V test stations tuned to: 4ns lised) optimal timing 8ns to fast 8ns too slow working point photo oelectrons (norma bias voltage [V] 14

15 Ion Feed Back due to e - ionising residual gas atoms ion produces bunch of photoelectrons at PC cluster of hits with 2-3ns delay we find: very low IFB very good tube vacuum Hits Per Ev vent 4 4. Strobe Scan H5244 response to LED pulses with varied delay Very low IFB <<1% Raw hits Clusters Poisson estimate Ion Feedback x Ion Feed Back from Strobe Scan <IFB> =.4% spec: max. 1% Delay [ns] Ion Feed Back [% ] 15

16 Dark Count specification: DC < 5kHz/cm 2 H5169: 7.3 khz/cm 2 H51618: 1. khz/cm 2 safety margin: ~ factor 1 before we exceed 1% occupancy 3 Dark Count from 5M events high red sensitivity increased IFB prob out of 557 s exceed 5 khz/cm 2 : accepted outside spec: class B two types: high red sensitivity increased IFB probability accepted range: 5 2 khz/cm perfectly fine to be used in RICH Dark Count [khz/cm2] 16

17 Quantum Efficiency DEP Data Excellent blue sensitivity: 27nm> = 3.8% increase due to process tuning at DEP single most helpful improvement to RICH performance typical: average QE [%] <QE> per batch running <QE> (batch -25) 27 nm (per batch) RMS of batch spread 23.3% minimum: 2.% batch no. more tuning improvements: fill of sensitivity dip between UV and visible reduction of red 8nm anti-correlated to blue sensitivity cause of thermal e - -emission (dark count) 17

18 QE PDTF Test Setup Dark Box measurement of the photocurrent, referenced with calibrated photodiode Reference Photodiode Filter System Quartz-Tungsten Halogen Lamp photocurrent: <16nA image Ø: ~ 5mm Interlock Fused Silica Lens R L I [pa] I PD [pa] Shutter, 1nm BP filter, IR or VIS block, ND filter η q ( λ) = η PD q ( λ) I I ( PD ( λ) ( λ ) Bias [V] default: 1V cross-check: 22V (just below He ionisation i threshold) h differing DEP parameters: Bias: 9V Ø: 1-15mm large photo currents 18

19 QE LHCb Verification PDTF measurement: 7 wavelengths, 1nm bandpass filter error: 2% 76 measured.2 PDTF QE measurements typically matches DEP values within 3% PDTF measurements confirm shape of spectra & absolute values full trust in DEP measurements complication for few (9) production : atypical large IFB fakes higher QE corrected from measurements as 22V bias QE, ηq, (n no units) Quantum Efficiency - typical sample H6485: DEP H6485: PDTF H61211: DEP H61211: PDTF H653: DEP H653: PDTF H5452: DEP H5452: PDTF Wavelength λ / nm extreme case for illustration 22V 19

20 Photoelectron Efficiency Backpulse comparison of binary to analog event yield with constant light source binary: through readout chip npe analog: measurement of the charge pulse on the bias line Poisson <μ> capacity of whole chip: noise*1 4 wrt. single pixel Poisson fit to analog spectrum Results: efficiency = npe / <μ> strobe length efficiency 25ns 5ns PDTF 27 88% 94% events (production s) 1 CERN 24 84% 92% (prototype s) error estimation pending pedestal subtracted analog ph.el. spectrum photo electrons data fit an almost perfect match fit yields Poisson <μ> ADC counts 2

21 Conclusions Production & testing of >55 s has finished rigorous test programme with >97.8% of s accepted s meet requirements of LHCb RICH detectors Very good results for vacuum quality and Dark Count Excellent results on QE and S/N DEP QE results confirmed by PDTF commissioning is underway with 288 installed in RICH2 21