SiPM photosensor development for nEXO Thomas Brunner McGill - PowerPoint PPT Presentation

SiPM photosensor development for nEXO Thomas Brunner McGill University and TRIUMF TAUP 2019 – Toyama September 10, 2019

Searching for 0nbb in 136 Xe with liquid Xe TPC Liquid-Xe Time Projection Chamber (TPC) Cathode • Xe is used both as the source and detection medium. • Monolithic detector structure, excellent background Scintillation rejection capabilities. • Cryogenic electronics in LXe. • Detection of scintillation light and secondary charges. e- e- e- e- e- Ionization e- • 2D read out of secondary charges at segmented anode. e- e- e-e- e- e- e- • Full 3D event reconstruction using also scintillation light: 1. Energy reconstruction 2. Position reconstruction 3. Event Multiplicity Segmented Anode September 10, 2019 Thomas Brunner – TAUP 2019 2

Energy measurement (EXO-200 data) Scintillation vs. ionization, 228 Th calibration: Reconstructed energy, 228 Th calibration: ALPHA CUT Q ββ = 2458 keV • Anticorrelation between scintillation and ionization in LXe known since early EXO R&D and now standard in LXe detectors [E.Conti et al. Phys Rev B 68 (2003) 054201] Rotation angle determined weekly using 228 Th source data, defined as angle which gives best rotated resolution • • EXO-200 has achieved ~ 1.15% (arxiv:1906.02723) energy resolution at the double-beta decay Q value in Phase II September 10, 2019 Thomas Brunner – TAUP 2019 3

Searching for 0nbb in 136 Xe in LXe EXO-200: nEXO: • • EXO-200 first 100-kg class ββ experiment. Proposed 5-ton liquid Xe TPC. • • ~110kg active volume, LXe TPC with ~80% Xe-136. Enriched in Xe-136 at ~90%. • • Located at the WIPP mine in NM, USA. Designed to take full advantage of LXe TPC concept. Aim to reach sensitivity of ~10 28 years. • • Operated 2011 – 2018 → demonstrated key performance parameters for 0nbb search. • SNOLAB cryopit preferred location by collaboration. Lower limit on half-life of 3.5 x 10 25 years with its • • Design of nEXO well advanced. entire dataset (arxiv:1906.02723). Neutrino #20: A. Pocar – nEXO design R. Saldanha – nEXO sensitivity Neutrino #7: M. Jewell – EXO-200 results September 10, 2019 Thomas Brunner – TAUP 2019 4

The nEXO detector • Next-generation neutrinoless double beta decay detector • 5 t liquid xenon TPC similar to EXO-200 (50x the size) • SiPM for 175nm scintillation light detection, ~5m 2 SiPM array in LXe • Tiles for charge read out • In-cold electronics inside TPC in liquid Xe • 3D event reconstruction • Combine charge and light readout. Goal → s /E of 1% at Q-value. Picture: 10 x 10 cm 2 tile prototype JINST 13, P01006 (2018) charge Tile simulation: arXiv:1907.07512. readout pads (anode) Field shaping rings Cathode 14 130 m cm SiPM ‘staves’ covering the barrel Ø13 m September 10, 2019 Thomas Brunner 5 nEXO at the SNOLAB Cryopit nEXO pre-CDR, arXiv:1805.11142 nEXO TPC

Choice of Photosensor for nEXO EXO-200 used 500 Bare APDs VUV sensitive SiPM for nEXO • • ~ 1500 V bias 30 - 80 V bias High Gain (10 5 – 10 6 ) • • Low gain (G~200) • • Large (dG/G)/dT ~ 5%/K Lower (dG/G)/dT ~ 0.6%/K • • Large (dG/G)/(dV/V) ~ 15 Lower (dG/G)/(dV/V) ~ 0.3 • • VUV photon detection efficiency per VUV photon detection efficiency per area, up to 15% area, 25%* • • Low leakage current at LXe temperature Dark noise and correlated noise * Accounting for inactive area Individual photon counting with high gain and low Noise goes up with increased capacitance, while signal noise. Resolution limited by dark counts and size remains constant, difficult to reach σ/E ~ 1%. correlated avalanches September 10, 2019 Thomas Brunner – TAUP 2019 6

Photon Detection Efficiency Requirements To achieve 1% energy resolution, an overall 3% photon detection efficiency is required, consisting of two parts: • Photon detection efficiency (PDE) of SiPM • Determined by filling factor, transmittance, quantum efficiency and trigger efficiency. • Can be measured by a standalone setup. • Photon transport efficiency (PTE) • Detector geometry • Reflective electrodes in TPC • Reflectivity of SiPM ε light > 3% For VUV photons, more than 50% will be reflected on SiPM surface, assuming Si-SiO 2 interface. Light Detection Efficiency [%] September 10, 2019 Thomas Brunner – TAUP 2019 7 arxiv:1805.11142

SiPM R&D for nEXO • SiPM PDE (at VUV region) and nuisance parameters (in cold) o Stanford U. o TRIUMF o Erlangen o BNL o IHEP o U. Mass. IEEE TRANS. NUC. SCIENCE, VOL. 62, NO. 4, AUGUST 2015 • Reflectivity of SiPM o In vacuum or N 2  Tested SiPMs • IHEP • TRIUMF ➢ FBK o In liquid xenon • NUV, VUV-LF-HD, VUV-STD-HD • U. Alabama ➢ Hamamatsu • Erlangen • VUV3, VUV4 • UMASS September 10, 2019 Thomas Brunner – TAUP 2019 8 Nuclear Inst. and Methods in Physics Research, A 940 (2019) 371

PDE Measurements nEXO key parameters (1805.11142): A, Jamil, et al. IEEE Trans.Nucl.Sci. 65, 2823 (2018) G. Gallina et al. Nucl. Instrum. Meth., 940, 371 (2019) • Center of wavelength: 180 nm. • FBK-VUV-LF shows higher PDE, comparing with VUV4 from Hamamatsu. • The uncertainty is dominated by quantum efficiency of the reference PMT. September 10, 2019 Thomas Brunner – TAUP 2019 9

Dark Noise and Correlated Avalanches nEXO key parameters (1805.11142): HPK VUV4 HPK VUV4 A, Jamil, et al. IEEE Trans.Nucl.Sci. 65, 2823 (2018) G. Gallina et al. Nucl. Instrum. Meth., 940, 371 (2019) • To achieve 1% energy resolution, the SiPM correlated avalanches (CA) need to be below 20%. • VUV4 from Hamamatsu has low CA than FBK-VUV-LF, thus can be operated at a higher over-voltage. • Dark noise rates for both type devices are comfortably below nEXO requirement of < 50Hz/mm 2 . September 10, 2019 Thomas Brunner – TAUP 2019 10

Reflectivity Measurements SiPM reflectivity in vacuum SiPM reflectivity in liquid xenon Hamamatsu VUV4 • • 252 Cf fission sources used to produce Oscillation due to SiO 2 layer, negligible in LXe. scintillation light in LXe. • Lower specular reflectivity for VUV4, comparing • to FBK SiPMs. Specular reflectivity decreases with angle of incidence. • Similar diffuse reflections between VUV4 and FBK SiPMs. September 10, 2019 Thomas Brunner – TAUP 2019 11

SiPM Performance under E-field η PDE Gain JINST 13, T09006, 2018 η PDE CT • In nEXO, SiPMs will be exposed to external E-fields up to ~20 kV/cm. • SiPM performance in various E-fields at cryogenic temperatures (~150K) have been tested in CF 4 . η PDE • The tested SiPMs show good stability under the influence of PDE different electric field strengths. • Need to test in LXe and understand if surface charge buildup is an issue. 0 5 10 15 20 25 30 E [kV/cm] September 10, 2019 Thomas Brunner – TAUP 2019 12

Large Area SiPM Readout • Requirements • Single photoelectron detection capability. R= 0.19 SPE • Low electronics noise (< 0.1 p.e.) • Analog readout prototype testing • Up to 6 cm 2 SiPMs can be read out with a single front end channel in either parallel or series configuration. • 2.5 mW/ch front end power meets the power requirement. • Provides valuable information for the ASIC design. Six 1 cm 2 R= 0.12 SPE FBK SiPM on a ceramic carrier board September 10, 2019 Thomas Brunner – TAUP 2019 13

Analog SiPMs - baseline solution for nEXO Prototype SiPM Tile • Integrate SiPMs into ‘tiles’ (~10 x 10 cm 2 ). ASIC (ZENON) for SiPM readout under design (BNL) • ASIC chip to read out tile. • System on Chip • 16 channel • • Tiles mounted on ‘stave’ (~20 x 120 cm 2 ). Peak detection • Analog to digital conversion • On-chip LDOs • Staves mounted inside LXe behind field cage. Prototype silicon interposer Conceptual design of the photo detector system underway September 10, 2019 Thomas Brunner 14

Beyond baseline nEXO R&D – 3DdSiPMs • A SPAD is a Boolean detector: digital information available at the sensor level • With a digital SiPM , each SPAD is coupled one-to-one with its individual readout circuit. • • Photon to bit conversion at the sensor level Control over each SPAD: faulty or radiation damaged • Improved noise immunity = shut off • • Output capacitance is not an issue (compared to SiPM) Lower dead time (sense-quench-recharge < 10 ns) • • Single photon counting mitigated No trigger = Low power consumption September 10, 2019 Thomas Brunner – TAUP 2019 15

Summary and Outlook • VUV sensitive SiPM is the photodetector of choice for the nEXO experiment. • R&D efforts in the collaboration show that some devices can already meet the nEXO requirements on PDE and correlated noise. • Reflectivity of the SiPM in vacuum and LXe is actively being investigated. • R&D on SiPM performance in high electric field and large area readout are underway. • nEXO is moving quickly towards a conceptual design for the photodetector system. • R&D ongoing for beyond-baseline technology. September 10, 2019 Thomas Brunner – TAUP 2019 16