LLNL-PRES-741373This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

Neutrinoless DoubleBetaDecaywithnEXO:ExperimentConcept,R&D,andSensitivityLNGSSeminar

SamueleSangiorgio

November 8, 2017

More details in arXiV:1710.05075

LLNL-PRES-7413732

NeutrinoPhysics

Knowns Unknowns

Profoundconsequences:• physicsbeyondtheStandardModelPhysics• originofthematter/antimatterasymmetryintheuniverse

§ n flavorchange§ Non-zeronmasses§ 3lightinteractingneutrinos§ Observed n fromatmospheric,reactor,solar,supernovae,beam,outerspace

§ Absolutenmasses§ nmassordering§ n nature:Majorana orDiracparticles?

§ Sterileneutrinos?§ CPviolation?§ Whynmuchlighterthanotherfermions?

§ …

LLNL-PRES-7413733

DoubleBetaDecay

Decay Q i.a. %48Ca→48Ti 4.271 0.18776Ge→76Se 2.040 7.882Se→82Kr 2.995 9.296Zr→96Mo 3.350 2.8100Mo→100Ru 3.034 9.6110Pd→110Cd 2.013 11.8116Cd→116Sn 2.802 7.5124Sn→124Te 2.228 5.64130Te→130Xe 2.533 34.5136Xe→136Ba 2.458 8.9150Nd→150Sm 3.367 5.6

LLNL-PRES-7413734

Neutrinoless DoubleBetaDecay(0nbb)d(n)

d(n)

u(p)

e−

e−

νe

νe

u(p)

W−

W−

d(n)

d(n)

u(p)

e−

e−

u(p)

W−

W−

Standard Model

+

+

+

+

+

+

+

+

-

-

ν

ν

Neutrino-less

+

+

+

+

+

+

+

+

-

-

§ bb0n observationimplies:– Leptonnumbernonconservation– Existenceofnewclassofparticles:Majorana fermions

LLNL-PRES-7413735

0nbb andNeutrinoMass

effective Majorana neutrino mass

§ Underassumptionof0nbb beingmediatedbyalightMajorana n exchange:

≈

phase space factor~ Q5

nuclear matrix elements » uncertainties

Also,arXiv:1705.01945,A.Caldwelletal

LLNL-PRES-7413736

0nbb DetectionSignatures

§ Mono-energeticlineatQbb inthesumelectron-energyspectrum

§ Localizedinteraction

§ Position(e.g.correlateswithsourcedistribution)

§ Emissionoftwocorrelatedelectrons

§ Daughternuclideproduced

§ Constantdecayrate,uncorrelatedwithotherevents

ββ2ν ββ0ν

Two electrons sum energy (keV)

Topological discrimination requiring 2 “blobs”: 9

nd

),

LLNL-PRES-7413737

0nbb with136Xe§ 136Xecanbeemployedinarangeofhighly-scalabledetectors,aspartofabroad,world-wideprogramemployingmultipleisotopes/technologies

§ Existing136XeexperimentsreachsensitivitiesofT1/2>5x1025yr,withnext-generationexperimentsaimingfor~1028yr

Liquid Xe TPCs:

EXO-200 nEXO

Liquid (organic) scintillators:KamLAND-Zen

KamLAND2-Zen

Gas Xe TPCs:

NEXT-100/NEXT-ton PandaX 200 PandaX 1kFrom D. Moore

LLNL-PRES-7413738

LiquidXe TPCs

LLNL-PRES-7413739

LargeLXe TPCs:aTechnologyforDiscovery§ ALXe TimeProjectionChamberlikenEXO allowsamulti-parametermeasurement:1. Interactionenergy fromcombinedionization/scintillation

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

LLNL-PRES-74137310

LargeLXe TPCs:aTechnologyforDiscovery§ ALXe TimeProjectionChamberlikenEXO allowsamulti-parametermeasurement:1. Interactionenergy fromcombinedionization/scintillation2. Interactionmultiplicity i.e.Single-Site(SS)orMulti-Site(SS)

Multiplicity can be used to characterize backgrounds

LLNL-PRES-74137311

LargeLXe TPCs:aTechnologyforDiscovery§ ALXe TimeProjectionChamberlikenEXO allowsamulti-parametermeasurement:1. Interactionenergy fromcombinedionization/scintillation2. Interactionmultiplicity i.e.Single-Site(SS)orMulti-Site(SS)3. Stand-offdistancefrominteraction3Dposition

Energy [keV]

Standoff [mm]100 200 300 400 500 600

Cou

nts

2−10

1−101

10

210

310

410

510

610

710 SS Standoff

Cou

nts

10

10

External backgrounds rapidly reduced by Xeattenuation

Internal events (signal or background) uniformily distributed

LLNL-PRES-74137312

LargeLXe TPCs:aTechnologyforDiscovery§ ALXe TimeProjectionChamberlikenEXO allowsamulti-parametermeasurement:1. Interactionenergy fromcombinedionization/scintillation2. Interactionmultiplicity i.e.Single-Site(SS)orMulti-Site(SS)3. Stand-offdistancefrominteraction3Dposition4. Particletype

LLNL-PRES-74137313

LargeLXe TPCs:aTechnologyforDiscovery§ ALXe TimeProjectionChamberlikenEXO allowsamulti-parametermeasure:1. Interactionenergy fromcombinedionization/scintillation2. Interactionmultiplicity i.e.Single-Site(SS)orMulti-Site(SS)3. Stand-offdistancefrominteraction3Dposition4. Particletype

§ Homogenousdetectors

kg 150kg5000kg

2.5MeV γattenuation length8.5cm =

130 cm“EXO-200”

“nEXO”

LLNL-PRES-74137314

BuildingonEXO-200Experience§ Performance:

— Energyresolution:1.23%s/Qbb

— FractionofSSevent:~20%— Electronlifetime~3ms

§ Multi-parameteranalysis

§ Backgroundcomposition1. Th+U backgroundfromexternal

components2. 137Xe(cosmogenic)3. 222Rn

§ Backgroundmodelfromfitmatchpre-datatakingbackgroundpredictionsfromradioassay

Method 232Th cntsinQββ±2·σββ

238U cntsinQββ±2·σββ

EXO-200data 10.3-13.9 5.3-7.1EXO-200radioassay 0.5-7.7 2.0-9.5Pre-dataprediction 0.9-10.3 6.3-26.8

LLNL-PRES-74137315

nEXO Design

A5000kgenriched(90%)LXe TPC,directlyextrapolatedfromEXO-200

EXO-2003.7x1025 ysensitivity

90%CL,177.6kg.y.arXiv:1707.08707

46cm

130cm

nEXO9.2x1027 yproj.sens.

90%CL,after10y.arXiv:1710.05075

LLNL-PRES-74137316

nEXO Design

ProcessEquipment

Accesstunnel

Watershield

Undergroundcavern

Supportstructure

Outercryostat

Innercryostat

TPC

Vacuum

Refrigerant

LXe

LLNL-PRES-74137317

nEXO TechnologicalImprovements

1.3me- drift

Chargereadoutstrips(anode)

SiPM `staves’coveringbarrelbehindfield-shapingrings

InLXeelectronics(chargeandSiPMs)

Cathode&HV

LLNL-PRES-74137318

HighVoltageR&DTestSetups30l LXe BernHVtestsetupnowatCarletonU. with

cryogeniccamerasUpper viewportjust below LXeLevel.

Lower viewportand Cathode tip

Anode connectedto oscilloscopeglitch detectoror HV probe setup

400ccLXe HVsetupatSLAC

Max800kgLXe setupatLLNLtoaccommodatefullornear-fullsizepartshorizontally

158 cm 14-40 cm

TestofbreakdownvoltageinLXefordifferentsmallsizegeometries

HVtestsinLXe fordifferentfull-nEXO diametersizegeometriesHVtestsof~30cm

scalegeometries

LLNL-PRES-74137319

HighVoltage&TPCR&D

§ Sparkmitigation:ensurestableoperationat-100kV

§ ProtectionofelectronicsandcomponentsincaseofHVbreakdown

§ TPCdesign:high-reflectivityandopticallyopenfieldcage

§ Lowradioactivity

hexagon

prototype

Novel high-resistivity Sifield cage (SLAC)

LLNL-PRES-74137320

Photosensors R&D§ ~4m2 ofVUV-sensitiveSiPMs

§ NoHVrequired§ Largergain&lowernoisethanAPDs

LLNL-PRES-74137321

ChargeReadoutR&D

Chargewillbecollectedonarraysofstripsfabricatedontolowbackgrounddielectricwafers

- Self-supporting/notension- Built-onelectronics(onback)- Farfewercables- Ultimatelymorereliable,lowernoise,

loweractivity

LLNL-PRES-74137322

ChargeReadoutPrototyping

ResultsoffirstprototypetestingatarXiv:1710.05109

LLNL-PRES-74137323

nEXO MonteCarloSimulations§ DetailedGEANT4MonteCarloincludesallimportantcomponents

§ Reconstruction:— 1%energyresolution— 3mmclusteringà 10%SSfractions— >10mselectronlifetime

§ Validationviafullmodelingofthecharge(arXiv:1710.05109)andlightreadout

LLNL-PRES-74137324

BackgroundSources

§ Long-livedradionuclides

§ Cosmogenicradio-nuclides

§ Neutrino-inducedbackgrounds

§ 214Bifrom222Rninsteady-state

§ Neutronactivationfrom(a,n)reactions

LLNL-PRES-74137325

UU92238

4.5 GyUU92

234

245.5 ky

ThTh90234

24.1 dThTh90

230

75.38 ky

226881 602 y

RaRa

234m91

1.17 minPaPaα α

α

α

222863.82 d

RnRn

PoPo84218

3.1 minPoPo84

214

164.3 μsPoPo84

210

138 d

PbPb82214

26.8 minPbPb82

210

22.2 yPbPb82

206

Stable

20680

8.32 minHgHg

218851.5 sAtAt

83 BiBi214

19.9 min83 BiBi210

5.01 d

81 TlTl210

1.3 min81 TlTl206

4.2 min

α

α α

α

α

α

α α

β-

β-

β- β-

β-

β-

β-

β-

β-

Uranium

Protactinium

Thorium

Radium

Radon

Astatine

Polonium

Bismuth

Lead

Thallium

Mercury

β-

Long-livedRadionuclides—238U,232Thgammaandbetadecays—137Cs,60Co,40KincludedbutnegligiblenearQbb

—Surfacebackgroundsmanageable(asinEXO-200)—2nbb

By User:Tosaka - File:Decay chain(4n+2, Uranium series).PNG, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=33293646By User:BatesIsBack - File:Decay_Chain_of_Thorium.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16983885

LLNL-PRES-74137326

NoAssumptionsonMaterialRadiopurity§ MeasurementcampaignisinprogresstoassayallmaterialsusedfornEXO constructionusingvarietyoftechniques

§ Onlymaterialswithmeasuredradioassay levelsareusedinthenEXO sensitivityestimation

Material Supplier Method K Th U 60Co[ppb] [ppt] U [ppt] [µBq/kg]

Copper Aurubis ICPMS/Ge/GDMS <0.7 0.13±0.06 0.26±0.01 <3.2Sapphire GTAT NAA 9.5±2.0 6.0±1.0 <8.9 -Quartz Heraeus NAA 0.55±0.04 <0.23 <1.5 -SiPM FBK ICPMS/NAA <8.7 0.45±0.12 0.86±0.05 -Epoxy∗ Epoxies Etc. NAA <20 <23 <44 -Kapton∗ Nippon Steel Cables ICPMS - <2.3 pg/cm2 4.7±0.7 pg/cm2 -HFE∗ 3M HFE-7000 NAA <0.6 <0.015 <0.015 -Carbon Fiber Mitsubishi Grafil Ge 550±51 58±19 19±8 -ASICs BNL ICPMS - 25.7±0.7 13.2±0.1Titanium TIMET Ge <3.3 57±5 <7.3 -Water SNOLAB Assumed <1000 <1 <1 -

LLNL-PRES-74137327

CosmogenicRadionuclides§ Aboveground:manageablewithpropermaterialhandlingtolimitcosmicraysexposure

§ Underground:137Xesteady-stateproductionfromncapture

FLUKAmodel

LLNL-PRES-74137328

Neutrino-inducedBackgrounds

§ Electron-neutrinoelasticscattering—Calculable—Small:~0.02SSevents/(FWHM.2000kg.y)

§ Charge-currentneutrinocapture—Estimated~20interactions/(2000kg.y)—Promptradiation:negligiblefractionofe- haverightenergy—Delayed136Csdecay:veryhighsingle-siterejection

§ Neutral-currentinelasticscattering

LLNL-PRES-74137329

Steady-state222Rn:an“external”background§ 222Rnfromemanationofmaterialsinthexenonpiping

§ Estimate~600atomssteady-stateinnEXO basedonEXO-200extrapolation

§ Threecomponents:— LXe insideTPC(17%)— LXe outsideTPC+Cathode(84%)

§ Bi-Potagging

Albert J., et al. Measurements of the ion fraction and mobility of α- and β-decay products in

V

V

LLNL-PRES-74137330

AnalysisandFitResults

Toy Data Best Fit ββν2 ββν0

Far components K40 Th232Internals U238Internals

Rn222 Xe137LXe Th232TPCVessel U238TPCVessel

Energy [keV]1000 1500 2000 2500 3000 3500

Cou

nts

2−10

1−101

10

210

310

410

510

610

710 SS Energy

Energy [keV]1000 1500 2000 2500 3000 3500

Cou

nts

2−10

1−101

10

210

310

410

510

610

710 MS Energy

Standoff [mm]100 200 300 400 500 600

Cou

nts

2−10

1−101

10

210

310

410

510

610

710 SS Standoff

Standoff [mm]100 200 300 400 500 600

Cou

nts

2−10

1−101

10

210

310

410

510

610

710 MS Standoff

§ Frequentistapproachtosensitivitycalculation§ ”Toy”experimentsgeneratedfromradioassay valuesandfitusinglog-likelihoodtechnique

§ Simultaneousfitofenergy,standoffdistance,andmultiplicity(SS/MS)

§ Exampleoffitresultforonetoyexperimentà

All standoffs All standoffs

All energies All energies

LLNL-PRES-74137331

FitResultsintheFWHMaroundQbb

3000 LXe volume [kg]10002000

LLNL-PRES-74137332

TheAdvantagesofaHomogenousDetector

§ Powerofusingasimultaneousfitofenergy,multiplicityandeventposition.Thisisnotaone-dimensionalpeaksearch.

§ OptimaluseoftheLXe mass:theinnermassprovidessensitivitytosignalwhiletheouterregionsallowtoconstrainthebackground.

LLNL-PRES-74137333

TheAdvantagesofaHomogenousDetector

§ Powerofusingasimultaneousfitofenergy,multiplicityandeventposition.Thisisnotaone-dimensionalpeaksearch.

§ OptimaluseoftheLXe mass:theinnermassprovidessensitivitytosignalwhiletheouterregionsallowtoconstrainthebackground.

LLNL-PRES-74137334

nEXO backgroundindexisnotasinglenumber!

§ SinglebackgroundindexnotsufficienttodescribenEXO§ Externalbackgroundsdominate

~3x10-4 cts/(FWHM.kg.y)

BackgroundindexvsLXe Mass

LLNL-PRES-74137335

nEXO backgroundindexisnotasinglenumber!

FornEXO,thesimplephysicsofg attenuationinLXe,coupledwithmulti-parameterdiscrimination,drivesthebackgroundestimation

~3x10-4 cts/(FWHM.kg.y)

BackgroundindexvsLXe MassMajorana Demon./GERDAarXiv:1710.11608/1710.07776

GoalforLEGEND-1000&CUPID

~ Background free

1 cts/tonne in 10 y

10 cts/tonne in 10 y

LLNL-PRES-74137336

EstimatedBackgroundBudget

§ SameprocedurevalidatedforEXO-200

§ Internalcomponentsdominate,asexpected

§ Severalradioassay entrieswithonly90%CLlimit(moremeasurementsmayimprovetheestimatedbackground)

Backgroundbudgetintheinner2000kg

LLNL-PRES-74137337

SensitivityandDiscoveryPotentialResults

Livetime [y]0 2 4 6 8 10

[y]

1/2

TββνXe

013

6

2610

2710

2810 y27 10×9.2

y253.7x10arXiv:1707.08707v1

nEXO Sensitivity, 90% C.L.

, 50% Prob.σnEXO Discovery Potential, 3

EXO-200 Sensitvity, 90% C.L.

Allowedmassesfromoscillations:90%CL,D.V.Forero etal,PRD90(2014)093006andM.Tortolaprivatecomm.;UnquenchedgA;SeearXiv:1710:05075fordetailsonNME

Majorana neutrinomasssensitivityin10y

nEXO 10y:<mbb><5.7-17.7meV at90%CL

§ Exclusionlimitat90%CLcomputedasthemedianupperlimitofanensembleof104 toyexperimentsandwithoutassumingWilks’stheorem

5.7 x 1027 y

LLNL-PRES-74137338

The(Small)RoleofEnergyResolution

[%]ββ/QσResolution 0.4 0.6 0.8 1 1.2 1.4 1.6

[y]

1/2

TββνXe

013

6

5

6

7

8

9

10

11

12

13

14

152710×

nEXO

EXO

-200

nEXO SensitivityvsEnergyResolution Countsfrom2nbb vsEnergyResolution

§ Onlyrelativelysmallimprovementfromimprovedenergyresolution

§ Furtherimprovementsnotcriticaltoreachcompellingsensitivity

§ 2nbb isalmostnegligibleinnEXO:0.34countsin10yearsintheentireLXe

§ Rapidlyworsenwithincreasingenergyresolution

LLNL-PRES-74137339

Sensitivitywithimprovedbackgrounds

Backgrounds in inner 2000 kg [cts/(FHWM kg y)]5−10 4−10 3−10

[y]

1/2

TββνXe

013

6

0

5

10

15

20

25

30

35

402710×

BaselineAggressive

only background-ββν2 • “Baseline”=radioassay-basedbackgroundestimate

• “Aggressive”=arisingfromplausibleimprovementsfromR&D

• “2nbb-only”=limitcase

• Powerlawfitgives:!"/$ ∝ "

&'.)*.

nEXO isnotassensitivetobackgroundsasanaïve +�scalingwouldimply.

LLNL-PRES-74137340

Conclusions§ 0nbb couldrevealfascinatingnewphysics

§ LXe TPCisaproventechnologyfor0nbb search.Multi-parameterreconstructioninahomogenousdetectorallowstooptimally”resolve”signalandbackgrounds.

§ nEXO’s sensitivityreachissolidlygroundedin— EXO-200experience— g attenuationinalargeLXe detector— measuredmaterialradiopurity

§ ThenEXO collaborationisreadytobuildanexperimentwith:— ultra-lowbackground:~3x10-4 cts/(FWHM.kg.y)intheinner2000kg— compellingdiscoverypotential(5.7x1027 yat3s)— reachontheMajorana neutrinomass~10meV range

§ Moredetailsin:nEXO Collaboration,“SensitivityandDiscoveryPotentialofnEXO toNeutrinoless DoubleBetaDecay”,arXiV:1710.05075

LLNL-PRES-74137341

ThenEXO CollaborationUniversity of Alabama, Tuscaloosa AL, USA

M Hughes, I Ostrovskiy, A Piepke, AK Soma, V VeeraraghavanUniversity of Bern, Switzerland — J-L VuilleumierBrookhaven National Laboratory, Upton NY, USA

M Chiu, G Giacomini, V Radeka, E Raguzin, T Rao, S Rescia, T TsangCalifornia Institute of Technology, Pasadena CA, USA — P VogelCarleton University, Ottawa ON, Canada

I Badhrees, M Bowcock, W Cree, R Gornea, K Graham, T Koffas, C Licciardi, D SinclairColorado State University, Fort Collins CO, USA

C Chambers, A Craycraft, W Fairbank Jr, D Harris, A Iverson, J Todd, T WaltonDrexel University, Philadelphia PA, USA

MJ Dolinski, E Hansen, YH Lin, E Smith, Y-R YenDuke University, Durham NC, USA — PS BarbeauUniversity of Erlangen-Nuremberg, Erlangen, Germany

G Anton, R Bayerlein, J Hoessl, P Hufschmidt, A Jamil, T Michel, M Wagenpfeil, T ZieglerIBS Center for Underground Physics, Daejeon, South Korea — DS LeonardIHEP Beijing, People�s Republic of China — G Cao, W Cen, Y Ding, X Jiang,

Z Ning, X Sun, T Tolba, W Wei, L Wen, W Wu, X Zhang, J ZhaoIME Beijing, People’s Republic of China — L Cao, X Jing, Q WangITEP Moscow, Russia

V Belov, A Burenkov, A Karelin, A Kobyakin, A Kuchenkov, V Stekhanov, O ZeldovichUniversity of Illinois, Urbana-Champaign IL, USA — D Beck, M Coon, S Li, L YangIndiana University, Bloomington IN, USA — JB Albert, S Daugherty, G VisserUniversity of California, Irvine, Irvine CA, USA — M Moe

Laurentian University,Sudbury ON,CanadaB Cleveland, A Der Mesrobian-Kabakian, J Farine, A Robinson, U Wichoski

Lawrence Livermore National Laboratory, Livermore CA, USAO Alford, J Brodsky, M Heffner, A House, S Sangiorgio

University of Massachusetts, Amherst MA, USAS Feyzbakhsh, S Johnston, CM Lewis, A Pocar

McGill University, Montreal QC, Canada — T Brunner, Y Ito, K MurrayOak Ridge National Laboratory, Oak Ridge TN, USA — L Fabris, RJ Newby, K ZiockPacific Northwest National Laboratory, Richland, WA, USA

I Arnquist, EW Hoppe, JL Orrell, G Ortega, C Overman, R Saldanha, R TsangRensselaer Polytechnic Institute, Troy NY, USA — E Brown, K OdgersUniversité de Sherbrooke — F Bourque, S Charlebois , M Côté, D Danovitch,

H Dautet, R Fontaine, F Nolet, S Parent, JF Pratte, T Rossignol, J Sylvestre, F VachonSLAC National Accelerator Laboratory, Menlo Park CA, USA

J Dalmasson, T Daniels, S Delaquis, A Dragone, G Haller,LJ Kaufman, A Odian, M Oriunno, B Mong, PC Rowson, K Skarpaas

University of South Dakota, Vermillion SD, USA — J Daughhetee, R MacLellanStanford University, Stanford CA, USA

R DeVoe, D Fudenberg, G Gratta, M Jewell, S Kravitz, G Li, A Schubert, M Weber, S WuStony Brook University, SUNY, Stony Brook NY, USA — K Kumar, O Njoya, M TarkaTechnical University of Munich, Garching, Germany — P Fierlinger, M MarinoTRIUMF, Vancouver BC, Canada

J Dilling, P Gumplinger, R Krücken, Y Lan, F Retière, V StricklandYale University, New Haven CT, USA — D Moore