EXO-200 and nEXO - vip-doll.ru August/Session 21.08 A/34_talk-belov.pdf · EXO-200 and nEXO...

EXO-200 and nEXO

Vladimir Belov, ITEP & MEPhIfor EXO-200 and nEXO

collaborations

17th Lomonosov Conference, Moscow, 21 August 2013

21.08.2015 V.Belov EXO-200 and nEXO 2

2ν mode: a conventional 2nd order process in Standard Model

0ν mode: a hypothetical process can happen only if: <mν> ≠ 0, ν = ν |ΔL|=2, |Δ(B-L)|=2

Simulated double beta decay spectrumP.Vogel. arXiv:hep-ph/0611243

To reach high measurement sensitivity for 0ν mode one requires, • High energy resolution• Large Isotope mass• Low background

Double beta decay


Energy resolution is poorer than the crystalline devices (~ factor 10), but...Monolithic detector. Xenon can form detection medium, allow self shielding,

surface contamination minimized. Very good for large scale detectors.Has high Q value. Located in a region relatively free from natural

radioactivity.Isotopic enrichment is easier. Xe is already a gas & 136Xe is the heaviest

isotope.Xenon is “reusable”. Can be purified & recycled into new detector (no crystal

growth). Minimal cosmogenic activation. No long lived radioactive isotopes of Xe.Energy resolution in LXe can be improved. Scintillation light/ionization

correlation.Particle identification. Slightly limited, but can be used to tag alphas from Rn

chain.

… admits a novel coincidence technique. Background reduction by Ba daughter tagging.

Why xenon


80.6% 136Xe T = 167 KP = 147 kPaρ = 3.0 g/cm3

High purity HFE7000 > 50 cm

25 cm

EXO-200 detector


The EXO-200 TPC

• Field shaping rings: copper• Supports: acrylic• Light reflectors/diffusers: Teflon• APD support plane: copper; Au (Al) coated

for contact (light reflection)• Central cathode, U+V wires: photo-etched

phosphor bronze• Flex cables for bias/readout: copper on

kapton, no glue

Comprehensive material screening program

• 38 U triplet wire channels (charge)

• 38 V triplet wire channels, crossed at 60o (induction)

• 234 large area avalanche photodiodes (APDs, light in groups of 7)

• Wire pitch 3 mm (9 mm per channel)

• Wire planes 6 mm apart and 6 mm from APD plane

• All signals digitized at 1 MS/s, ±1024S around trigger

• Drift field 376 V/cm

40 cm40 cm

Two almost identical halves reading ionization and 178 nm scintillation, each with:

xz

y


● Signal finding. Digital filters are used on waveforms from U,V wires and APDs● Parameters of pulses (t, E) are estimated for both charge and light● Pulses are combined into clusters producing position, multiplicity (SS or MS) and energy.● Position is used in form of Standof Distance (SD) that is distance from any cluster to the nearest wall

Event reconstruction

V-wire signalsV-wire signals

U-wire signalsU-wire signals

APD signalsAPD signals

Charge clustersCharge clusters

Scintillation clustersScintillation clusters

Linked

tu

β

γ

SingleSiteEvents(SS)

tu

γ

MultipleSiteEvents(MS)

Efficiency to get into SS: 2β0ν ~90%γ 2.5MeV ~30%

But we don’t throw MS events away! We use them in the fit to help predict background


APD denoising

1.53 % in SS at 0νββ Q-value


Rotation angle chosen to optimize energy resolution at 2615 keV

Properties of xenon cause increased scintillation to be associated with decreased ionization (and vice-versa)

E. Conti et al. Phys. Rev. B 68 (2003) 054201

Use projection onto a rotatedaxis to determine event energy

Combining ionization and scintillation


We used gamma sources Cs, Co, Th, Ra

Energy resolution model

Resolution is dominated by by constant term (noise)

At Qββ (2458 keV):σ/Ε = 1.53 % (SS)σ/Ε = 1.65 % (MS)

Energy calibration

Data with sources is fitted by model PDFs SS/MS ratio agrees with 10% accuracy Measured source activity is 4% accurate


Data takingC

um

ula

tive

live

tim

e [d

ays]

Previous results

Accumulation of data in science «Run 2» from Oct'2011 till Sep'2013.«Golden» data is 447.60 ± 0.01 days livetimeThat corresponds to 100 kg y in⋅ 136Xe exposure.


2β0ν measurement

Single site

Multi site

Efficiency to 2β events85 %

Full livetime477.6 d100.0 kg y

2β events~37000

The lowest background index among comparable detectorsBI = 1.7 ± 0.2 × 10-3 keV-1 kg-1 y-1

[Nature 510, 229 (2014)]

13

2β0ν measurement

T1/20νββ > 1.1 x 1025 yr

〈 mββ 〉 < 190 – 450 meV (90% C.L.)

[Nature 510, 229 (2014)]

Pro

file

likel

ihoo

d

Backgrounds in ± 2σ ROI

Th chain 16.0

U chain 8.1

Xe-137 7.0

Total 31.1 ± 3.8


Comparison of 2β0ν

EXO-200:Nature 510, 229 (2014)

GERDA Phase 1: PRL 111 (2013) 122503

KamLAND-Zen:PRL 110 (2013) 062502 KK&K Claim:Mod. Phys. Lett., A21 (2006) 1547


Searching for majoron

Phys.Rev D90 9, 092004 (2014)


EXO-200 results● Operated a 100 kg scale LXe TPC for 2 years● Discovered a double beta decay of 136Xe● Made the most precise measurement of its halflife● Measured residual backgrounds are very low● Reached design (anticorrelated) energy resolution, σ/E(Q)=1.5%● Achieved stable electron lifetime of ~3 ms or better● Utilized self-shielding in monolithic detector● Demonstrated power of β/γ discrimination (SS/MS)

● Implemented novel detector solutions and analysis techniques● 500 LAAPDs for VUV (175 nm) scintillation detection● Photo- etched, charge collection wires, cathode, and fasteners● Epoxy- poned, kapton flat cable feedthroughs● HFE- 7000 thermal bath and radiation shield● Ultra- light design, no solder joints


nEXO concept

● 5 tonnes of enriched LXe● Monolithic design dramatically improves

performance with size● Using enhanced self- shielding● x100 better T

1/2 sensitivity

● < 1% energy resolution● no central cathode● *no* Ba tagging (initially)

Conceptual design for SNOLab150 kg

5000 kg

2.5MeV γ attenuation length (8.5cm)


nEXO R&D: TPC

Charge readout tiles

Silicon Photo Multipliers

TCP: ~ 1.3 m x 1.3 m

Key features:● single drift volume● thin Copper or Carbon vessel● minimal use of plastics● charge collected by pads on top● 10 ms electron lifetime● scintillation collected by SIPMs on side barrel behind the field cage● VUV reflection● Optimization of fiducial volume

nEXO R&D in full swing


nEXO R&D: Charge• Charge readout structures on low background substrates• SS/MS discrimination (readout pitch)● No tension and microphonics (not wires)

Prototype Charge Readout Quartz Tile LXe Test Apparatus


nEXO R&D: Light• High light collection efficiency (>15% at 175 nm)• Ultra‐low background (~ppt levels for Th & U)• VUV sensitive SiPMs from FBK, Hamatsu, Ketek or Hamamatsu MEG devices or Wave-Length-Shifters• Already measuring samples

FBK SiPMs, 1st gen Hamamatsu MEG


nEXO R&D: Electronics• Cold electronics close to the detector• improve energy resolution to 1%• low background, low noise• keep required power low enough• deliver all the signals without much loss• multiplexing to reduce cabling/feedthroughs

Cold charge readout ASIC Prototype circuit for SiPMs


EXO-200 and nEXO projected sensitivities

Combining all ourexperience and thebest technologies

we plan

T1/2

= 6 · 1027 yr

in 5 years of

counting

Majorana

neutrino mass

<mββ

> sensitivity

of 7- 18 meV

nEXO is an active international R&D program for a x100 the sensitivity of EXO- 200!

University of Alabama, Tuscaloosa AL, USA - T. Didberidze, M. Hughes, A. Piepke, R. TsangUniversity of Bern, Switzerland - S. Delaquis, R. Gornea, T. Tolba, J-L. Vuilleumier California Institute of Technology, Pasadena CA, USA - P. Vogel Carleton University, Ottawa ON, Canada - V. Basque, M. Dunford, K. Graham, C. Hargrove, R. Killick, T. Koffas, C. Licciardi, D. SinclairColorado State University, Fort Collins CO, USA - C. Chambers, A. Craycraft, W. Fairbank, Jr., T. WaltonDrexel University, Philadelphia PA, USA - M.J. Dolinski, Y.H. Lin, E. Smith, Y.-R YenDuke University, Durham NC, USA - P.S. BarbeauIHEP Beijing, China - G. Cao, W. Cen, X. Jiang, L. Wen, J. ZhaoUniversity of Illinois, Urbana-Champaign IL, USA - D. Beck, M. Coon, S. Homiller, J. Ling, J. Walton, L. Yang Indiana University, Bloomington IN, USA - J. Albert, S. Daugherty, T. Johnson, L.J. Kaufman, T. O’ConnerUniversity of California, Irvine, Irvine CA, USA - M. MoeITEP Moscow, Russia - V. Belov, A. Burenkov, M. Danilov, A. Dolgolenko, A. Karelin, A. Kuchenkov, V. Stekhanov, O. ZeldovichLaurentian University, Sudbury ON, Canada - B. Cleveland, A. Der Mesrobian-Kabakian, J. Farine, B. Mong, U. WichoskiUniversity of Maryland, College Park MD, USA - C. Davis, C. Hall University of Massachusetts, Amherst MA, USA - J. Abdollahi, S. Feyzbakhsh, S. Johnston, A. Pocar, D. ShyIBS Center for Underground Physics, Daejeon, South Korea - D.S. LeonardSLAC National Accelerator Laboratory, Menlo Park CA, USA - M. Breidenbach, R. Conley, T. Daniels, J. Davis, A. Dragone, K. Fouts, R. Herbst, A. Johnson, K. Nishimura, A. Odian, C.Y. Prescott, A. Rivas, P.C. Rowson, J.J. Russell, K. Skarpaas, M. Swift, A. Waite, M. WittgenUniversity of South Dakota, Vermillion SD, USA, – R. MacLellanStanford University, Stanford CA, USA - T. Brunner, J. Chaves, R. DeVoe, D. Fudenberg, G. Gratta, M. Jewell, S.Kravitz, D. Moore, I. Ostrovskiy, A. Schubert, K. Twelker, M. WeberStony Brook University, SUNY, Stony Brook, NY, USA – K. Kumar, O. Njoya, M. TarkaTechnical University of Munich, Garching, Germany - W. Feldmeier, P. Fierlinger, M. MarinoTRIUMF, Vancouver BC, Canada – J. Dilling, R. Krücken, F. Retière, V. Strickland


What else from EXO-200?

Following 2 accidents at the WIPP mine, EXO- 200 personnel is

now granted regular access to the site and recovery operations

are ongoing

● EXO-200 can still contribute to the leading set of experiments

● Upgrades had bee installed before the accident:● Radon suppression system for air around the detector● Upgraded electronics (could get to 1% energy resolution)

● Approx. 2 years of data are still being worked on:● Cosmogenic backgrounds● Gamma, beta and alpha backgrounds

26

Efficiency to 2β 58 % (87 %)

Full exposure127.6 сут23.14 кг л

2β events18984

Reanalyzed Run 2a data from (PRL 109, 032505, 2012)

2β2ν measurementThe most precise measurement of halflife of any isotope to date

T1/22νββ = 2.165 ± 0.016(stat) ± 0.059(sys) × 1021 yr

[PRC 89, 015502 (2014)]total relative uncertainty 2.85%


Xenon purity

Непрерывная циркуляция ксенона через высокотемпературные очистители SAES с использованием специально сконструированного насоса.

Neilson et al. (2011) arXiv:1104.5041v1

Среднее время жизни электрона ~3 мс обеспечивает на максимальном времени дрейфа 110 мкс уменьшение сигнала <3%.

Восстановление после остановок занимает несколько дней


nEXO expected backgrounds and signalsSimulated nEXO spectrum near single-site ROI:

Full 4.8 tonnes, 5 yr

Central 1 tonneonly, 5 yr

T1/20νββ=

1.8·1027 yr

● Have developed Geant4 simulation for nEXO, using experience gained from EXO-200

● Spectra on right show expected backgrounds in 5 yr exposure, and 0νββ at discovery threshold

● Background calculation assumes measured activity for detector materials

● This procedure was verified with EXO-200 data, and assumes several improvements for nEXO


Ba tagging

2448 keV214Bi

2615 keV208Tl

Simulated nEXO spectrum near single-site ROI:

Full 4.8 tonnes, 5 yr

● In addition, R&D to develop techniques to identify Ba daughter nucleus of 0νββ decay (“Ba tagging”) is continuing

● Candidate 0νββ events would be identified in real time and daughter Ba ion collected by probe inserted into the TPC at the decay location

● Identity of Ba daughter can be confirmed spectroscopically

•This technology would eliminate all non-ββ backgrounds near ROI•Could extend ultimate reach of nEXO into the normal hierarchy since full 5 tonne mass would be background free


Ba tagging

Twelker et al., arXiv:1407.0618

Several techniques are currently being pursued:

• Tagging from solid Xe by fluorescence spectrum

• Resonance ionization spectroscopy (RIS):

• Also studying ion extraction and tagging from high pressure Xe gas

389.7 nm553.5 nm1064 nm

To Time of FlightSpectrometer

Ba+

Wavelength (nm)

Typical time of flight spectrum:

Fluorescence of Ba in SXe:

Excited by 558 nm laser

<128 atoms

<28 atoms<18 atoms

<6 atoms

Cold probe

Solid Xe

Liquid Xe Ba+

Detect single ion or atom on the probe with

laser-induced fluorescence

Co

un

ts

EXO-200 and nEXO - vip-doll.ru August/Session 21.08 A/34_talk-belov.pdf · EXO-200 and nEXO...

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