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