The nEXO detector: design overview Andrea Pocar University of - PowerPoint PPT Presentation

TAUP 2019 — 16th International Conference on Topics in Astroparticle and Underground Physics 9-13 September, 2019 — Toyama, Japan The nEXO detector: design overview Andrea Pocar University of Massachusetts, Amherst Andrea Pocar - UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019

Outline β • Neutrinoless double beta decay • Tonne-scale experiments: nEXO • The nEXO detector • concept and design • from EXO-200 to nEXO: new technology • sensitivity • Outlook β Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 2

0 νββ decay and neutrino mass (Seesaw I mechanism) current experiments 
 (~100 kg, T 1/2 ~10 26 y) “tonne-scale” 
 ( T 1/2 ~10 28 y ) observation of 0 νββ decay • massive, Majorana neutrinos • lepton number violation ( Δ L = 2) • new mass mechanism • new mass scale 1 = G 0 ν ( Q, Z ) | M 0 ν | 2 < m ββ > 2 0 νββ rate T 0 ν 1 / 2 • absolute neutrino mass 
 (model dependent) Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 3

Dura lex, sed lex N A = 6 . 022 × 10 23 Amedeo Avogadro • DBD candidate isotopes: 48 → 150 grams/mole • 10 28 nuclei = 16,600 moles → 800—2,500 kg • Real-life non-idealities: 
 detection efficiency, isotopic fraction, backgrounds, detector live time, …. • Need ~tonne(s) of DBD-decaying isotope Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 4

The nEXO detector (artist view in the SNOLAB cryopit) Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 5

Liquid Xenon Time Projection Chambers (TPCs) • Monolythic 2.5MeV γ • In-line purification of xenon attenuation length: 8.5cm: Liquid xenon TPC’s • active self-shielding (improves with size) • good energy resolution 
 β , ββ combining ionization+scintillation • particle ID (scintillation vs. ionization) • event topology (single-/multi-site events) γ Scale-up: EXO-200 (200 kg) ➔ nEXO (5,000 kg) see R Saldanha, in Neutrino #20 for details on the physics case for nEXO Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 6

from EXO-200 to nEXO see M. Jewell, in Neutrino #7 for latest EXO-200 results EXO-200 concluded its operations in Dec 2018 Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 7

nEXO: a 5-tonne LXe TPC charge readout in-xenon cold pads (anode) electronics (charge and SiPMs) SiPM ‘staves’ coating the barrel (behind the cathode field cage) 1.3 m electron drift d i a m e t e r 
 ( 1 . 3 m ) Cathode placed at one end of the cylinder to maximize the continuous volume of LXe Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 8

Cryogenics, xenon purity Cryogenics LXe vessel immersed in >30 tonnes of HFE7000 fluid 
 (design inherited from EXO-200) • light-weight xenon vessel • gamma-ray and neutron shielding • thermal stability Xenon purity (chemical and radioactive) • >10 ms drifting electron lifetime …… minimal use of plastics • ~5 ms reached by EXO-200 (with thin teflon reflectors) • 600 steady-state radon atoms in the bulk • ~200 steady state atoms achieved in EXO-200 • need to limit decays of radon progeny at the cathode Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 9

nEXO publications: detector, sensitivity, R&D - "Simulation of charge readout with segmented tiles in nEXO" arXiv:1907.07512 - "Characterization of the Hamamatsu VUV4 MPPCs for nEXO" arXiv:1903.03663, Nucl Inst Meth A 940 371 (2019) - “Imaging individual Ba atoms in solid xenon for barium tagging in nEXO” Nature 569 (2019) 203 * - "Study of Silicon Photomultiplier Performance in External Electric Fields“ JINST 13 (2018) T09006 - “VUV-sensitive Silicon Photomultipliers for Xe Scintillation Light Detection in nEXO” IEEE Trans NS 65 (2018) 2823 - “nEXO pCDR” arXiv:1805.11142 (2018) - "Sensitivity and Discovery Potential of nEXO to 0 νββ decay" Phys. Rev. C 97 065503 (2018) - "Characterization of an Ionization Readout Tile for nEXO“ J.Inst. 13 P01006 (2018) - "Characterization of Silicon Photomultipliers for nEXO“ IEEE Trans. NS 62 1825 (2015) * Not nEXO baseline Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 10

nEXO TPC: highlights 10 cm charge collection tiles ~6 cm SiPM arrays Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 11

Ionization charge detection JINST 13, P01006 (2018) Prototype 3mm pitch, crossed strips deposited on a 10 cm x 10 cm quartz tile produced and tested in liquid xenon. 80 fF at crossings 0.86 pF between 10 μ m adjacent strips 3 mm no shielding Frisch grid Bi-207 source Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 12

Ionization charge readout details arXiv:1907.07512 Flow chart of the simulation of electron drift and readout in nEXO The sensitivity only mildly depends on the chosen pitch of the strips Proper inclusion of the induction signals allows a ~20-30% sensitivity boost Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 13

Scintillation light detection EXO-200 used 500 Bare LAAPDs. nEXO uses VUV-sensitive SiPMs • 30 - 80 V bias • High Gain (10 5 – 10 6 ) • Lower (dG/G)/dT ~ 0.6%/K • Lower (dG/G)/(dV/V) ~ 0.3 • ~ 1500 V bias • Low gain (G~200) • VUV photon detection efficiency • Large (dG/G)/dT ~ 5%/K per area, up to 15% • Large (dG/G)/(dV/V) ~ 15 • Dark noise and correlated noise • VUV photon detection efficiency per area, 25%* Individual photon counting with • Low leakage current at LXe temperature high gain and low noise. Resolution * Accounting for inactive area limited by dark counts and Noise increases with capacitance, correlated avalanches while signal size remains constant, difficult to reach σ /E ~ 1%. Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 14

Photon detection efficiency 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, an overall 3% photon detection efficiency is required, consisting of two parts: • PDE of SiPMs • Photon transport efficiency nEXO goal Some 1cm 2 VUV devices meet nEXO specs, with a bias of ~30V see T. Brunner, in New Technologies #1 for more details on photosensor development for nEXO Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 15

Scintillation light mirrors The absence of a traditional’ teflon reflector together with the placement of SiPMs on the xenon vessel barrel behind the TPC field cage requires the electrodes, especially the field shaping rings, to be made reflective Losses in photon transport efficiency need to be compensated with increased SiPM PDE Looking at thin-film aluminized electrodes Measurements of SiPM reflectivity in LXe also ongoing see T. McElroy, in DM 14 New Ideas in Sub-GeV dark see T. Brunner, in New Technologies #1 for more matter for “post-nEXO” ideas on light detection details on photosensor development for nEXO Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 16

Cold, in-LXe readout electronics Charge Light Six 1cm2 FBK SiPM on a ceramic carrier board prototype charge readout system <1% energy resolution R= 0.12 SPE p r e background discrimination l i m i n 200 electrons rms a r y 2 MS/s ASIC development at BNL and SLAC (alternative approach developed at IHEP) Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 17

nEXO sensitivity vs. exposure (preliminary baseline) see J Orrell, poster 422 for details on the background models and control for nEXO 5.0x10 25 yr 
 arXiv1906.02723 - g A = g Afree =-1.2723 - Band is the envelope of NME: EDF: T.R. Rodríguez and G. Martínez-Pinedo, PRL 105, 252503 (2010) ISM: J. Menendez et al., Nucl Phys A 818, 139 (2009) IBM-2: J. Barea, J. Kotila, and F. Iachello, PRC 91, 034304 (2015) QRPA: F. Š imkovic et al., PRC 87 045501 (2013) SkyrmeQRPA: M.T. Mustonen and J. Engel PRC 87 064302 (2013) Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 18

stay hungry, Outlook my friend • The search for LNV and 0 νββ decay continues to be a central mission of the nuclear/particle/fundamental symmetries community worldwide • Xenon is a prime candidate for a tonne-scale 0 ν DBD experiment • EXO-200 was the first 100-kg -scale experiment to run. 
 It has inspired the 25-fold scale up, nEXO, and concluded its run in December 2018 with rich analysis still ongoing • Liquid xenon TPC’s have successfully scaled up 100-fold in ~15 years • The nEXO design is mature and grounded in proven technology. The nEXO design is ready and mature and aims at becoming a leading technology with very substantial US and international support • nEXO has developed a firm 5-tonne detector ‘baseline’, inclusive of a detailed background model and solid (somewhat conservative) sensitivity estimation. 
 R&D on critical detector items steadily progressing Andrea Pocar — UMass Amherst TAUP — Toyama, Japan — 9-13 September 2019 � 19