Silicon Photomultiplier tests in LN, LAr Janicsk o J ozsef - PowerPoint PPT Presentation

Silicon Photomultiplier tests in LN, LAr Janicsk´ o J´ ozsef February 6, 2009

GERmanium Detector Array (GERDA) Is a double beta decay experiment • We operate HPGe detectors in LN/LAr. • Low countrate low background experiment, extreme radiopurity required • LAr is a well known scintillator  1 . cooling liquid  2 . passive shielding • LAr is: 3 . scintillator  February 6, 2009 1/31

February 6, 2009 2/31

Ar scintillation spectrum ρ (LAr) = 1.4 g/cm 3 n(LAr)= 1.24, 40000 photon/MeV February 6, 2009 3/31

Heidelberg setup LArGe@MPI-K: * LAr LAr Schematic system description GAr GAr • Dewar Ø 29 cm, h=65 cm (43 L – total volume ) • Light detection: WLS (VM2000 + PST/TPB) stainless HV signal steel optical + PMT(8“, ETL 9357-KFLB ) fiber • Active volume Ø 20 cm, h=43 cm § 19 kg LAr (13,5 L) lead shield • Shielding: 5 cm lead (+ 10 cm BP for n) PMT +15 mwe underground Measurements: Internal source WLS source tube vis UV NaI – detector used for: 1) coincidence measurements; 2) reference measurements. External source Dewar February 6, 2009 4/31

Goals PMT’s, in general are: • ”Dirty” (radioactive), not suitable for low background experiments • They don’t work at cryogenic temperatures • Requires HV (problems in Ar atmosphere) SiPM could be a replacement of PMT’s with higher radiopurity, no HV, UV sensitive etc. Goal is to reproduce the results of the Heidelberg (GERDA) group with SiPM’s : at least 1000 p.e. / MeV February 6, 2009 5/31

Hamamatsu MPPC February 6, 2009 6/31

Photon Detection Efficiency February 6, 2009 7/31

Setup • Bias circuit and amplifier built on one PCB • Preamp. works in LN • works with a coax. cable between the SiPM and the PCB • in the final setup SiPM in LN, preamp. at RT February 6, 2009 8/31

SiPM properties at LN temperature February 6, 2009 9/31

Dark rate v. temperature The main reason for cooling down a Si device is the thermal noise. We don’t have cryostat, I just wait until the temperature stabilizes in the dewar. A Pt-100 is attached to the SiPM S10365-11-100 dark rate [cps] 6 10 5 10 4 10 3 10 2 10 10 100 150 200 250 300 temperature [K] Effect of ambient light is not excluded, during overnight measurement the rate dropped below 1Hz. = ⇒ Up to 6 orders of magnitude reduction in dark rate. February 6, 2009 10/31

Xtalk Simply recording the dark counts h1_tmp h1_tmp Dark counts at RT Entries 1906180 Entries 1906180 Mean Mean 277 277 RMS RMS 181.3 181.3 4 10 3 10 2 10 10 1 RT: 0 500 1000 1500 2000 2500 3000 ADC counts hps0 hps0 hps1 hps1 hps0 hps1 Entries Entries 4698 4698 Entries Entries 4698 4698 Mean Mean 0.982 0.982 Mean Mean 1.127 1.127 2 2 10 10 RMS RMS 1.38 1.38 RMS RMS 1.488 1.488 10 10 1 1 LN: -1 0 1 2 3 4 5 6 7 8 9 -1 0 1 2 3 4 5 6 7 8 9 RT: I estimate 21% LN: 40 - 50% or is not dark rate (can not be measured) February 6, 2009 11/31

Relative efficiency RT LN IR laser at RT h2 h2 IR laser in LN h2 h2 Entries Entries 10000 10000 Entries Entries 10000 10000 Mean Mean 116.7 116.7 Mean Mean 114.8 114.8 counts RMS RMS 89.23 89.23 120 RMS RMS 69.66 69.66 200 100 80 150 1.9 p.e. 2.1 p.e. 60 100 40 50 20 0 850nm IR laser 0 0 50 100 150 200 250 300 350 400 450 500 50 100 150 200 250 300 350 400 450 500 a.u. 400nm Blue LED No visible efficiency drop at LN temperature (compared to RT) Looks like we can have low dark rate and high QE in the same time February 6, 2009 12/31

Pulse shape in LN RT LN Can be explained by structure of the SiPM. The polysilicon resistor is temperature dependent. February 6, 2009 13/31

Photon counting RT LN Photon counting h2 h2 Photon counting h2 h2 Entries Entries 10000 10000 Entries Entries 10000 10000 Mean Mean 0.01105 0.01105 Mean 0.007811 Mean 0.007811 a.u. a.u. 90 RMS RMS 0.006868 0.006868 RMS RMS 0.00307 0.00307 250 80 70 200 60 150 50 40 100 30 20 50 10 0 0 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 Amplitude (V) Amplitude (V) February 6, 2009 14/31

Photon counting • The peak amplitude cannot be measured accurately • By integrating the area under the pulse (offline analysis) I could restore the resolution RT LN Photon counting Photon counting h3 h3 h2 h2 Entries Entries 10000 10000 Entries Entries 10000 10000 Mean Mean 0.01105 0.01105 180 Mean Mean 0.941 0.941 a.u. RMS RMS 0.006868 0.006868 RMS RMS 0.3588 0.3588 250 160 140 200 120 100 150 80 100 60 40 50 20 0 0 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Amplitude (V) Area (a.u.) February 6, 2009 15/31

DAQ and SiPM • PIXIE4 DAQ (75 MHz, 14 bit) can record the pulse-shape without any “ charge amplifier ” • Cooling the SiPM gives longer pulse, better for the DAQ Typical pulse shapes for the 1600 and 100 pixel Si PM in LN. Recorded with the DAQ. February 6, 2009 16/31

DAQ and SiPM • The resolution is not so good as with the oscilloscope, but I still can distinguish 20 photon peaks. • Amplitude calculated with trapezoidal energy filter. hpx hpx Photon number Entries Entries 4.161728e+07 4.161728e+07 Mean Mean 20.17 20.17 RMS RMS 11.17 11.17 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 5 10 15 20 25 30 35 40 Nb. of Photons MCA spectrum recorded with the DAQ. The light intensity (LED) was increased in more (4) steps. February 6, 2009 17/31

DAQ and SiPM Charge-sensitive preamplifier February 6, 2009 18/31

DAQ and SiPM Resolution with the charge-sensitive preamplifier Photon spectrum with charge preamplifier and DAQ February 6, 2009 19/31

... but the resolution deteriorates too fast htmp htmp Cha_MCAEnergy[0] Entries Entries 20000 20000 Mean Mean 3801 3801 RMS RMS 3036 3036 3 10 2 10 10 1 -1 10 -2 10 0 2000 4000 6000 8000 10000 12000 14000 February 6, 2009 20/31

Pulseshape analysis • Time resolution is important to distinguish slow and fast scintillation. Delayed signal expected up to 2-3 µ s 15000 600 14000 500 13000 400 12000 300 11000 10000 200 9000 100 8000 0 7000 50 100 150 200 250 300 50 100 150 200 250 300 February 6, 2009 21/31

Damage caused by LN Si PM is held in place by soft epoxy resin, which doesn’t like LN temperatures. One with 100 pixels is gone ... Still, survived many ( ∼ 100) cooling cycles February 6, 2009 22/31

Light detection in LAr (preliminary) February 6, 2009 23/31

Direct light detection 178 nm, -95 o C February 6, 2009 24/31

Direct light detection 2 SiPM’s in LAr at 5 cm distance from a Th228 source. Dark counts removed by coincidence trigger. Overnight measurement (about 14 h) h2 h2 h2 h2 Entries Entries 2165 2165 Entries Entries 258 258 Mean Mean 434.4 434.4 Mean Mean 404.8 404.8 12 4 RMS RMS 985.4 985.4 RMS RMS 363.3 363.3 3.5 10 3 8 2.5 6 2 1.5 4 1 2 0.5 0 0 0 5000 10000 15000 20000 25000 30000 0 5000 10000 15000 20000 25000 30000 ADC counts ADC counts LAr + Th source left, right LN with no source compared to LN • LN + Th source 2-3 fold increase • LAr, no source 2 fold increase • LAr + Th source ∼ 10 fold increase in the countrate with coincidence trigger February 6, 2009 25/31

Two step WL shifting Idea: 128 nm = ⇒ Blue scintillator ( ∼ 400 nm) = ⇒ Green WLS fiber • Blue scintillator: VM2000 foil coated with TPB → high efficiency • Green WLS fiber → 3% trapping efficiency 3.5 m attenuation length February 6, 2009 26/31

Principle Number of photons detected: N = Y F (1 − S ) Ce − l/λ R 1 /S Q where: • Y = 50000, photon yield / MeV in LAr • F = 1.35 TPB fluor efficiency • S = 0.1 - 0.05 surface covered by the fibers • C = 0.034 - 0.07 WLS trapping efficiency • l = 10 m (one fiber) • λ > 3 . 5 m, attenuation length • R = 0.2 - 0.99 reflectivity of TPB or VM2000 • Q = 0.4 QE of the SiPM at 500 nm February 6, 2009 27/31

My Setup • 2 x 10m WLS fiber total surface: 2 x 314 cm 2 • effective area: 4 x 110 cm 2 • 4 x SiPM • linear preamps integration done by the DAQ • 1) Al foil with TPB coating (home-made) • 2) VM2000 foil from CREST February 6, 2009 28/31

Th228 spectrum + VM2000 Preliminary: th228 + VM2000 + WLS a.u. Background 0.007 0.006 0.005 0.004 0.003 0.002 0.001 0 0 10 20 30 40 50 Nb. of Photons February 6, 2009 29/31

Conclusion SiPM’s: • they are easy to use • excellent resolution • they do work in LN • I could see some light in LAr A more serious test-setup is under construction: • Gas tight dewar is under construction • mechanical parts being prepared in the workshop • electronics under development February 6, 2009 30/31

? • Joint project for development of the read-out electronics ? • Could we have SiPM optimized for LN temperature ? • improoved UV sensitivity ? • LARGE area SiPMs ? February 6, 2009 31/31