Vancouver Linear Collider Workshop University of British Columbia, Canada July 20 th 2006 Scintillator/WLS Fiber Readout with Geiger-mode APD Arrays Pablo Bauleo, Rey Nann Ducay, Eric Martin, David Warner, Robert J. Wilson, Qinglin Zeng, Department of Physics Colorado State University Stefan Vasile aPeak Inc. 63 Albert Road, Newton, MA

R.J.Wilson, Colorado State University Overview Motivation Recap 7-GPD cluster measurements with MINOS-type bars Recap single square GPD measurements New single-chip 64-fiber readout Summary

R.J.Wilson, Colorado State University Motivation WLS readout of scintillator strips basic component of several existing detectors (MINOS, CMS-HCAL); option for LC muon/calorimeter systems Geiger-mode Avalanche photodiodes (GPDs) –Pros: Large pulse (~volt); high quantum efficiency; relatively fast; compact; low mass; low voltage operation (~10s volts); modest physical plant; magnetic field insensitive; compatible with CMOS -> cheap? –Cons: High dark count rate; small pixels ( microns); unproven. Growing number of developers… –SiPM: Dolgoshein et al., Russia – some production level; tested by several groups –MRS APD (Metal Resistor Silicon APD): INR, Moscow; manufactured by CPTA, Russia – few hundreds; tested by several groups –MPPC (Multi-Pixel Photon Counters): Hamamatsu Photonics, Japan – a few R&D devices; one group? (possibly others in Japan) –GPD: aPeak, USA – a few R&D devices; examined at CSU

R.J.Wilson, Colorado State University 7-pixel GPD cluster (2005) Seven 150  m GPDs; ~16% of 1 mm fiber area Individual readout of each pixel Response to cosmic rays measured at CSU with modified MINOS bar + WLS Average individual pixel Detector Efficiency, DE ~14% Cluster DE ~65% GPD cluster Clear fibers Active Quenching Circuit (AQC)

R.J.Wilson, Colorado State University Single 162 x 162  m 2 Square GPD (2005) DE – measured detection efficiency DCR – Dark Count Rate DE1000 – effective DE if the quenching time is 1000 ns (typical of unquenched devices) Single 162  m x 162  m GPD  5 photons/event

R.J.Wilson, Colorado State University New 64-fiber Readout (16-GPD/pixel) aPeak goal is high efficiency, high- density, compact, cheap WLS/fiber readout primarily for non-calorimetric use 64 x 1 mm 2 fiber readout on one chip Each pixel is a cluster of sixteen 160x160  m 2 GPDs on 240  m centers Geometrical efficiency for 1.2 mm diameter fiber ~ 0.36 (0.45 for 1 mm) Signal out proportional to number of hit GPDs; allows hit threshold tuning (not optimized for calorimetry) No active quenching circuitry 1.2 mm 10 mm

R.J.Wilson, Colorado State University GPD Testing/Comparison Use PMT (EMI 911B) response to cosmics & 550 nm LED as a reference PMT used to read out WLS fiber embedded in MINOS bar (courtesy FNAL); fiber extends 22” beyond end of the bar Charge spectrum collected for ~vertical cosmic rays Same PMT fitted with a mask with 1 mm diameter circular hole; placed 80 cm from 550 nm LED LED voltage and pulse width adjusted to replicate cosmic ray charge spectrum; process repeated with different LED settings to produce range of intensities Replace the PMT with GPD array at same position LED allows testing at much higher event rates and controllable range of intensities

R.J.Wilson, Colorado State University PMT Cosmic Ray/LED charge distributions Charge spectrum of ~ vertical cosmic rays (VCR) in 300 ns gate; use this to define unit of 1 VCR; mean charge ~11 pC (PMT gain ~10 7 ) Same PMT fitted with a mask with 1 mm diameter circular hole; placed 80 cm from 550 nm LED LED voltage (2.5 V) and pulse width (14.5 ns) adjusted to ~ replicate charge spectrum of 1 VCR (180 ns gate) LED distribution lacks high tail of cosmic ray sample LED settings adjusted to shift peak for range VCR; shape and spectrum of true multiple VCRs unknown No absolute calibration; Approx. 1 VCR = 200 “photons“ out of WLS 1 ADC bin = 0.25 pc Charge (ADC bins) Cosmics g180-s V - ADC0 LED

R.J.Wilson, Colorado State University GPD Signal GPD bias V 550 nm LED illumination 10x linear amplifier DC offset – origin unclear, depends on bias Single shotAverage many triggers

R.J.Wilson, Colorado State University GPD Cluster LED charge distributions 10x amplifier on the GPD output for timing measurements 29dB attenuator used to bring the signal into the ADC range LED rate – 30 Hz 500 ns ADC gate; pedestal 20 pC (bin 80) GPD cluster charge spectrum for ~ 1 & 4 VCR equivalent LED intensity; ~ 200 & 800 incident “photons”; ~ 4 & 16 “photons”/individual GPD 1,000 1,100 1,200 1,300 PIXEL45_g500ns_30dB_3vcr_325V_18ns_30hz - ADC0 1 VCR 4 VCR GPD bias V

R.J.Wilson, Colorado State University Pixel Charge vs. Intensity Linear for VCR Rollover corresponds to all GPDs in the cluster registering a hit; shape consistent with a model based on earlier single GPD DE measurements; Similar distribution seen if average peak voltage used instead of charge GPD bias V corrected for -29 dB attenuator but not 10x amplifier

R.J.Wilson, Colorado State University Detection Efficiency/Dark Count Rate For signal threshold voltage, V th –Dark Count Rate (DCR) from scaler –Detection Efficiency (DE) calculated from comparing discriminated pixel signal rate with/without pulse generator Fall off of at low V th due to high DCR and signal width Product of signal width (w) and dark count rate (DCR) reduces effective detection efficiency by factor ~(1-w*DCR) –e.g. for 300 ns & 1 MHz DE_eff = 0.7*DE Improve by lowering temperature Detection Efficiency & Dark Count Rate V th ( mV ) DE & DCR (MHz) DCR Note: GPD signal with 10x amplifier GPD bias V 95% DE 0.9 VCR 2.6 VCR 5.2 VCR Signal overlap

R.J.Wilson, Colorado State University Detection Efficiency vs. Charge

R.J.Wilson, Colorado State University Summary New aPeak high density readout (64 fibers/chip) Modest “calorimetric” response demonstrated; useful for threshold tuning High efficiency demonstrated but only for relatively high light levels at room temperature due to high dark count rate/long pulses Temperature dependence to be measured soon (starting this week) Progress, but not yet demonstrated to be competitive with other options Funding –LCRD funding - $14k = 4 weeks Dave Warner + trip to midwest –aPeak phase II funding: no-cost extension 7/06 -> 4/07; goal to test 64 fiber r/o with muon prototype (Dave planning a Fermilab trip soon) Related news – CSU group now part of T2K collaboration –ND280 (Near-Detector) will use Russian MRS APD and Japanese (HPK) MPPC –Testing of >10,00 at CSU; good training for LCD muon system!