neutrinoless double-β...ssi, august 2009 double-beta decay 11 the possibility of neutrinos-less...

NeutrinolessNeutrinoless doubledouble--ββdecaydecay

Giorgio GrattaPhysics Dept, Stanford

SSI, August 2009 Double-Beta decay 2

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Solar νKamLAND

Atmospheric νK2K

Minos et al.

Neutrinolessdouble beta

decay

Chooz/Palo Verde

information onCP is here

Our knowledge of the lepton mixing matrixOur knowledge of the lepton mixing matrix

θ12~32°θ13


Next challenges in neutrino physics:• absolute mass scale, • θ13 , choice of hierarchy, CP violation Mike Shaevitz

~3·10-3 eV2

solar~ 8·10-5eV2

solar~ 8·10-5eV2

~3·10-3 eV2

Our knowledge of the Our knowledge of the νν mass patternmass pattern

~2.8 eV

From tritium

endpoint(M

aintzand Troitsk)

~0.3 eV

From 0νββ

if νis M

ajorana

~1 eVFrom

WM

AP

Time of flight from

SN1987A

(PDG 2002)

23 eV


Endpoint mass measurementsEndpoint mass measurementsStudy the spectral shape near Study the spectral shape near

the endpoint of a the endpoint of a ββ decaydecay(note that the end(note that the end--point value ispoint value isgenerally generally notnot known well enoughknown well enough

to use its absolute position)to use its absolute position)

Measure the quantity:

22)(2i

iie

eff mUme ∑=ν

Principle almost as old as neutrino itself:E. Fermi, Z. Phys. 88 (1934) 161

If the experimental resolution is smaller than If the experimental resolution is smaller than mmii22--mmjj22then one should see a separate kink in thethen one should see a separate kink in thespectrum for each of the states spectrum for each of the states ii and and jj


Modern experiments use mainlyModern experiments use mainly eeHeT ν++→−3

231

a supera super--allowed transition with rather good combination of lowallowed transition with rather good combination of lowend point (Eend point (E00=18.6 =18.6 keVkeV) and short half life (T) and short half life (T1/21/2=12.3 yr)=12.3 yr)

Spectrometer has to have 1) very high resolutionSpectrometer has to have 1) very high resolution2) very high luminosity2) very high luminosity

(most of the statistics in(most of the statistics inthe spectrum is not used…)the spectrum is not used…)

electron energyelectron energy


Long history of measurements Long history of measurements that, for long time, have that, for long time, have been plagued by negative been plagued by negative central values for central values for mmνν2 (2 (effeff))

magneticspectrometers

electrostatic spectrometers

This is understood nowand the latest generationof experiments get resultsconsistent with mν2 (eff)=0

Mainz group:Mainz group:Ch.KrausCh.Kraus et al. et al. Nucl.PhysNucl.Phys. B 118 (2003) 482. B 118 (2003) 482Ch.WeinheimerCh.Weinheimer Nucl.PhysNucl.Phys. B 118 (2003) 279. B 118 (2003) 279

42)(2 /1.22.22.1 ceVm eff ±±−=ν)%95(/2.2 2)( CLceVm eff


New, very large electrostatic, integrating spectrometerNew, very large electrostatic, integrating spectrometerbeing built in Karlsruhe: “KATRIN”being built in Karlsruhe: “KATRIN”

Expected sensitivity0.20 - 0.25 eV(assuming systematics

are understood)

~2m tall~2m tallhumanhuman


5.63.367150Nd→150Sm8.92.479136Xe→136Ba34.52.533130Te→130Xe5.642.228124Sn→124Te7.52.802116Cd→116Sn11.82.013110Pd→110Cd9.63.034100Mo→100Ru2.83.35096Zr→96Mo9.22.99582Se→82Kr7.82.04076Ge→76Se0.1874.27148Ca→48Ti

Candidate Candidate Q Q AbundAbund..((MeVMeV)) (%)(%)

DoubleDouble--beta decay:beta decay:a seconda second--order processorder processonly detectable if firstonly detectable if firstorder beta decay isorder beta decay is

energetically forbiddenenergetically forbidden

Candidate nuclei with Q>2 Candidate nuclei with Q>2 MeVMeV


There are two varieties of ββ decay

2ν mode: a conventional2nd order process in nuclear physics

0ν mode: a hypothetical process can happen only if: Mν ≠ 0

ν = ν |∆L|=2 |∆(B-L)|=2

Since h

elicity

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ogel

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2νββ spectrum(normalized to 1)

0νββ peak (5% FWHM)(normalized to 10-6)

Summed electron energy in units of the kinematic endpoint (Q)

Background due to the Standard Model 2νββ decay

The two can be separated in a detector withgood energy resolution

0νββ peak (5% FWHM)(normalized to 10-2)


The possibility of neutrinosThe possibility of neutrinos--less decay wasless decay wasfirst discussed in 1937:first discussed in 1937:

E. E. MajoranaMajorana, , NuovoNuovo CimentoCimento 14 (1937) 17114 (1937) 171

G. G. RacahRacah, , NuovoNuovo CimentoCimento 14 (1937) 32214 (1937) 322

Even earlier the study of nuclear Even earlier the study of nuclear structure led to the conclusion that structure led to the conclusion that the 2 neutrino mode would have the 2 neutrino mode would have half lives in excess of 10half lives in excess of 102020 yearsyears

M.GoeppertM.Goeppert--Mayer, Phys. Rev. 48 (1935) 512Mayer, Phys. Rev. 48 (1935) 512

The idea of doubleThe idea of double--beta decay is almost as old as beta decay is almost as old as neutrinos themselves:neutrinos themselves:


Neutinoless double beta decay is not the only possible lepton non-conserving process:

ΔL = 2 ββ ββ decaydecayΔL = 0, ΔLf =1 Flavor oscillationsFlavor oscillations

μμ →→ eeγγΔL = 2, ΔLf =1 μμ-- + + ZZA A →→ ee+ + + + Z+2Z+2AA

Using oscillation data and the unitarity of the mixing matrix, one can derive estimated

rates for these processes:

0νββ and oscillations are most sensitive to leptonnon-conservation


−−+ ++′→ eeNN

AZ

AZ 2

++− ++′→ eeNN

AZ

AZ 2

+−

− +′→+ eNeN AZAZ 2

NeeN AZAZ ′→++ −

−−2

Note that along with the double Note that along with the double ββ-- decaydecay

there is also a there is also a ββ++ mode that in practice would appear mode that in practice would appear as a single or double electron captureas a single or double electron capture

All these processes are phaseAll these processes are phase--space suppressed respectspace suppressed respectto the to the ββ-- casecase and isotope fractions low in natural mix:and isotope fractions low in natural mix:

usually not consideredusually not considered


( )12

02

20

000

2/12 ,

−

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⎛−= νββνββνββνββν F

A

VGT Mg

gMZEGTm

If 0νββ is due to light ν Majorana masses

νββ0FM

νββ0GTM

can be calculated withincan be calculated withinparticular nuclear modelsparticular nuclear models

νββ0G a known a known phasespacephasespace factorfactor

andand

νββ02/1T

is the quantity to is the quantity to be measuredbe measured

∑=

=3

1

2

,i

iiie mUm ενeffective Majorana ν mass

(εi = ±1 if CP is conserved)


Much progress made recently in accuracy of nuclear matrix elemenMuch progress made recently in accuracy of nuclear matrix elements.ts.(e.g. was found that the main uncertainly in (R)QRPA calculation(e.g. was found that the main uncertainly in (R)QRPA calculations s comes from the single particle space around the Fermi surface. comes from the single particle space around the Fermi surface.

Can Can use the measured 2use the measured 2νββνββ TT1/21/2 to make a correction.to make a correction.))

Lower bound on TLower bound on T1/21/2used for used for 136136XeXe

Still, if/once 0Still, if/once 0νββνββ decay is discovered, the Tdecay is discovered, the T1/21/2 in more than onein more than onenucleus will be needed to pin down neutrino massesnucleus will be needed to pin down neutrino masses

F.SimkovicF.Simkovic et al. et al. Phys.Rev.C 77 (2008) 045503


Comparison of isotopes:Is there a super-DBD-isotope ?

2200102/1 ||),()( eemMZQGT

ννν =−

Expected 0νββ rates per mass vary within a factor ~ 4

QRPA(Simkovic et al. PRC 77, 2008)

~ factor 4

Figure adapted from Robertsonand Schoenert


In fact there are good reasons to claimIn fact there are good reasons to claimthat more than one isotope has to be that more than one isotope has to be measured to providemeasured to provide

•• reliable results reliable results

•• the neutrino the neutrino mass scalemass scale

•• understanding understanding of the 0of the 0νββνββmechanismmechanism

- Different isotopes havedifferent matrix elements

- 0νββ always implies newphysics (L violation)

- Differences between isotopesand e- angular correlationsprobe the internal mechanismcausing the decay

- Different isotopes(and techniques) havedifferent backgrounds

SSI, August 2009 Double-Beta decay 18Plot from Plot from AvignoneAvignone, Elliott, Engel arXiv:0708.1033 (2007), Elliott, Engel arXiv:0708.1033 (2007)

100kg-class detectors~100-200 meV sensit.

Klapdor et al. claim [0.17 – 0.45 eV]

EXO 1 ton, 5yr, 28 meV

EXO 10 ton, 10yr, 6 meV

Plot assumesMajorana neutrinos

For the first time there is a clear opportunity to make an importantdiscovery pushing the sensitivity to the 0.01 - 1 eV region


In the last 10 years there has been a transition

1) From a few kg detectors to 100s or 1000s kg detectorsThink big: qualitative transition from cottage industry

to large experiments

2) From “random shooting” to the knowledge that at least theinverted hierarchy will be tested

Discovering 0Discovering 0νββνββ decay:decay:Discovery of the neutrino mass scaleDiscovery of the neutrino mass scaleDiscovery of Discovery of MajoranaMajorana particlesparticlesDiscovery of lepton number violationDiscovery of lepton number violationExploration of high energy regime viaExploration of high energy regime via

the see saw mechanismthe see saw mechanism


ββββ decay experiments are at the leadingdecay experiments are at the leadingedge of edge of ““low backgroundlow background”” techniquestechniques

•• Final state ID: Final state ID: 1) “Geochemical”: search 1) “Geochemical”: search for an abnormal abundancefor an abnormal abundanceof (A,Z+2) in a material contaiof (A,Z+2) in a material containing (A,Z)ning (A,Z)

2) “Radiochemical”: store in a mine some m2) “Radiochemical”: store in a mine some material (A,Z)aterial (A,Z)and after some time try to findand after some time try to find (A,Z+2) in it(A,Z+2) in it

+ Very specific signature+ Very specific signature+ Large live times (particularly for 1)+ Large live times (particularly for 1)+ Large masses+ Large masses-- Possible only for a few isotopes (in the case of 1)Possible only for a few isotopes (in the case of 1)-- No distinction between 0No distinction between 0νν, , 22νν or other modesor other modes

•• “Real time”: “Real time”: ionization or scintillation is detected in the decayionization or scintillation is detected in the decaya) “Homogeneous”: source=detectora) “Homogeneous”: source=detectorb) “Heterogeneous”: b) “Heterogeneous”: sourcesource≠≠detectordetector

+ Energy/some tracking available (can distinguish modes)+ Energy/some tracking available (can distinguish modes)+ In principle universal (b)+ In principle universal (b)-- Many Many γγ backgrounds can fake signaturebackgrounds can fake signature-- Exposure is limited by human patienceExposure is limited by human patience


The Standard ModelThe Standard Model22ννββββ decay has beendecay has been

observed in many isotopes observed in many isotopes

†Results not in good agreement§Geochemical experiment*Radiochemical experiment$Decay NOT observed, lower limit reported

(2.0±0.6)•1021 *238U(1.4±0.7)•1020150Nd

>1.1•1022 90% CL136Xe$

(2.7±0.1)•1021 §(7.9±1.0)•1020 §

(6.1±3.5)•1020130Te†

(7.2±0.4)•1024 §128Te(2.9±0.4)•1019116Cd(5.7±1.2)•1020100Mo

(9.4±3.2)•1018 §

(2.1±0.6)•101996Zr

(9.6±1)•101982Se(1.77±0.12)•102176Ge(4.3±2.2)•101948Ca

T1/22ν (yr)Isotope

Table arbitrarily simplifiedfrom PDG


Candidate Detector Present (eV)nucleus type (kg yr) T1/20νββ (yr)

48Ca >5.8*1022 (90%CL)76Ge Ge diode ~47.7 >1.9*1025 (90%CL) 2.1*1023 (90%CL) 100Mo >5.8*1023 (90%CL)116Cd >1.7*1023 (90%CL)128Te TeO2 cryo >1.1*1023 (90%CL)130Te TeO2 cryo ~12 >3*1024 (90%CL) 1.2*1024 (90%CL) 1.2*1021 (90%CL)160Gd >1.3*1021 (90%CL)

Present Limits for 0Present Limits for 0νν double beta decaydouble beta decay


Klapdor-Kleingrothaus et al.NIM A 522 (2004)

PLB 586 (2004)

• 71.7 kg year - Bgd 0.11 / (kg y keV)• 28.75 ± 6.87 events (bgd:~60)• Claim:4.2σ evidence for 0νββ• (0.69–4.18) x1025 y (3σ)• Best fit: 1.19 x1025 y (NIMA 522/PLB 586)• PSA analysis (Mod. Phys. Lett. A21):

(2.23 + 0.44 – 0.31)x1025 y • Tuebingen/Bari group (PRD79):

mee /eV = 0.28 [0.17-0.45] 90%CL

A.M. Rotunno, TAUP09(PRD 79)

There is also a discovery claim (using There is also a discovery claim (using 7676Ge)Ge)

Significance and T1/2 depend on bgd description:

•Strumia & Vissani NPB726 (2005) •Chkvorets, PhD diss. Heidelberg (2008)

using more realistic background model⇒ peak significance: 1.3σ, ⇒ T1/2 = 2.2x1025 y


To reach ~ 10 meV very large fiducial mass (tons)(except for Te) need massive isotopic enrichment

Need to reduce and control backgrounds in qualitatively new waysthese are the lowest background experiment ever built

For no For no bkgndbkgnd

Scaling with Scaling with bkgdbkgdgoes like goes like NtNt

NtTm /1/1 02/1 ∝∝νββ

ν

( ) 4/102/1 /1/1 NtTm ∝∝ νββν

In addition a multiIn addition a multi--parameter experiment, if feasible,parameter experiment, if feasible,would provide information for cross checks withwould provide information for cross checks with

more than one single variable, if a discovery is made.more than one single variable, if a discovery is made.


Some large future experiments (a very broad brush)

DUSEL? GS?~1tonSee aboveMaGe/GeMa

G Sasso34.3 kgEres,2site tag, LAr shieldGerda†

SUSEL30-60kgEres,2site tag, Cu shieldMajorana†

76Ge

136Xe

130Te*

150Nd or 82Se

150Nd

Isotope

1-10ton

150 kg

204 kg

100 kg

56 kg

Fid mass

DUSEL?Ba tag, Track/Eres

WIPPTracking/EresEXO

G SassoE Res.CUORE

CanfrancFrejus

TrackingSuperNEMO‡

SNOlabSize/shieldingSNO+

LabMain principleExperiment

* No isotopic enrichment in baseline design† Plan to merge efforts for ton-scale experiment ‡ Non-homogeneous detector


Measurement of ΔT=E/C

~

85 c

m41 kg TeO2• nat. abundance of 130Te: 34%

• active mass: 11 kg of 130Te

Thermal coupling

Heat sink

Thermometer

Crystal absorber

Incident particle

130Te: Cuoricino(Gran Sasso)

Cryogenic detector


Cuoricino data taking completed….

60Co 130Te

• Cuoricino data taking successfully completed in 2008

• Full statistics statistics:18 kg x year of 130Te

• Background at 0νββ:0.18 ± 0.02 cts/(keV kg y)degraded α’s (60%)ext. 208Tl γ’s (40%)

• Limit on 130Te 0νββ decay:T1/2 > 2.94x1024 y (90% C.L.)mee< 0.2 – 0.98 eV

(M. Sisti, Taup 09)


… and CUORE construction started!

The CUORE building in hall A of LNGS

Cryostat order placed

988 TeO2 5x5x5 cm3 crystals => 741 kg TeO2 => 204 kg 130Te


3 m

4 mB (25 G)

20 sectorsSource: 10 kg of ββ isotopes

cylindrical, S = 20 m2, 60 mg/cm2

Tracking detector:drift wire chamber operating in Geiger mode (6180 cells)

Calorimeter: 1940 plastic scintillatorscoupled to low activity PMTs

Magnetic field: 25 GaussGamma shield: Pure Iron (18 cm)Neutron shield: borated water

+ Wood

NEMO 3 @ Modane: The ‘2νββ factory’…


….and its sources

116Cd 405 gQββ = 2805 keV

96Zr 9.4 gQββ = 3350 keV

150Nd 37.0 gQββ = 3367 keV

48Ca 7.0 gQββ = 4272 keV

130Te 454 gQββ = 2529 keV

natTe 491 g

Cu 621 g

2νββ decaymeasurement

Externalbackground

measurement12

00

01

02

030405

06

07

08

09

10

11

19

17

18

161514

13

100Mo 6.914 kgQββ = 3034 keV 0νββ decay search

82Se 0.932 kgQββ = 2995 keV

&


Results from NEMO3’s strongest source: 100Mo

V. Tretyak (Medex’09), also F. Mauger (Taup09)


From NEMO3 to SuperNEMO

Baseline: 82SeAlternatives: 150Nd, 48Ca


SuperNEMO at the new LSM

• 5 - 7 kg of ββ isotope per module• 20 - 22 modules for the full

detector for 100 – 150 kg of isotope in total

• modules surrounded by water shielding

• Location: LSM (France)• demonstrator operational 2011


Two large 76Ge Projects:GERDA Majorana

•‘Bare’ enrGe array in liquid argon • Shield: high-purity liquid Argon / H2O• Phase I: 18 kg (HdM/IGEX) / 15 kg nat.• Phase II: add ~20 kg new enr. Detectors;

total ~40 kg

•Array(s) of enrGe housed in high-purity electroformed copper cryostat

•Shield: electroformed copper / lead•Initial phase: R&D demonstrator

module: Total ~60 kg (30 kg enr.)

• open exchange of knowledge & technologies (e.g. MaGe MC)• intention to merge for O(1 ton) exp. ( inv. Hierarchy) selecting the best technologies tested in GERDA and Majorana

Physics goals: degenerate mass rangeTechnology: study of bgds. and exp. techniques

LoI


Novel Ge-detectors with advanced 0νββ-signal recognition & background suppression

Budjas et al. IEEE 2008

DEP89.2% ±0.9%

0νββ-likeγ-bgd

10.1%±0.7%

• 0νββ: point-like events

• Bgd: multi-site or partial energy deposition outside crystal

n-type detectors with 18-fold segmented electrodes

p-type with small readout electrode; Similar performance with thick-window BEGe detectors

R&D: LAr scintillation read out

(S. Elliott, A.Smolnikov, J. LiuTaup 2009)


3400 m.w.eunderground GERDA @ LNGS

Start commissioning: autumn 2009

Detector string Glove box & lock

Clean roomCryostat & μ-veto

Heat exchanger & pipes


Phases and physics reach

10 25

10 26

10 27

10 28

10 102

103

exposure (kg y)

T1/

2 (y

) (9

0% C

.L.,

no b

gd.)


• $300M of heavy water removed and returned to Atomic Energy of Canada Limited (every last drop)

• SNO detector to be filled with liquid scintillator– 50-100 times more light than Čerenkov

• linear alkylbenzene (LAB)– compatible with acrylic, undiluted– high light yield, long attenuation length– safe: high flash point, low toxicity– cheaper than other scintillators

• physics goals: pep and CNO solar neutrinos, geo neutrinos, reactor neutrino oscillations, supernova neutrinos, double beta decay with Nd

SNO+

(C. Krauss, Taup 09)


simulation:one year of data

0νββ Signal for = 0.150 eV

• 0.1% natural Nd-loaded liquid scintillator in SNO+ ⇒ 56 kg of 150Nd• Future: use of enriched 150Nd ?


The case for The case for 136136Xe in a large Xe in a large experimentexperiment

••No need to grow crystalsNo need to grow crystals••Can be reCan be re--purified during the experimentpurified during the experiment••No long lived No long lived XeXe isotopes to activateisotopes to activate••Can be easily transferred from one detector to Can be easily transferred from one detector to

another if new technologies become availableanother if new technologies become available••Noble gas: Noble gas: easy(ereasy(er) to purify) to purify••136136Xe enrichment easier and safer:Xe enrichment easier and safer:

-- noble gas (no chemistry involved)noble gas (no chemistry involved)-- centrifuge feed rate in gram/s, all mass usefulcentrifuge feed rate in gram/s, all mass useful-- centrifuge efficiency centrifuge efficiency ~~ ΔΔm.m. For For XeXe 4.7 4.7 amuamu


XeXe offers a qualitatively new tool against background:offers a qualitatively new tool against background:136136Xe Xe 136136BaBa++++ ee-- ee-- final state can be identified final state can be identified

using optical spectroscopyusing optical spectroscopy ((M.MoeM.Moe PRC44 (1991) 931)PRC44 (1991) 931)

BaBa++ system best studiedsystem best studied((NeuhauserNeuhauser, , HohenstattHohenstatt,,ToshekToshek, , DehmeltDehmelt 1980)1980)Very specific signatureVery specific signature

“shelving”“shelving”Single ions can be detectedSingle ions can be detectedfrom a photon rate of 10from a photon rate of 1077/s/s

••Important additionalImportant additionalconstraintconstraint

••Drastic backgroundDrastic backgroundreductionreduction

22PP1/21/2

44DD3/23/2

22SS1/21/2

493nm493nm

650nm650nm

metastablemetastable 47s47s


The The BaBa--tagging, added to a high resolution tagging, added to a high resolution XeXe imagingimagingdetector provides the tools to develop a backgrounddetector provides the tools to develop a background--freefree

nextnext--generation generation ββββ experimentexperiment

Assume an “asymptotic” Assume an “asymptotic” fiducialfiducial mass of mass of 10 tons of 10 tons of 136136Xe at 80%Xe at 80%

A somewhat natural scale:A somewhat natural scale:•• World production of World production of XeXe is ~40 ton/yris ~40 ton/yr•• Detector sizeDetector size•• 22••101033 size increase: good match to the size increase: good match to the

1010--22 eVeV mass regionmass region

Mainly going inMainly going inlight bulbs, light bulbs,

plasma displays andplasma displays andsatellite propulsionsatellite propulsion

To get started: EXOTo get started: EXO--200200an intermediate detector an intermediate detector withoutwithout BaBa taggingtagging


200 kg 200 kg 136136Xe test production completed in spring ’03 (80% enrichment)Xe test production completed in spring ’03 (80% enrichment)

••Largest highly enriched stockpileLargest highly enriched stockpilenot related to nuclear industrynot related to nuclear industry

••Largest sample of separated Largest sample of separated ββββisotope (by ~factor of 10)isotope (by ~factor of 10)


1 kV/cm

~570 ~570 keVkeV

EXO R&D showed the way to improved energy resolution in LXe: Use (anti)correlations between

ionization and scintillation signals


Anti-correlated ionization and scintillation improves the energy resolution in LXe

Ionization alone:σ(E)/E = 3.8% @ 570 keV

or 1.8% @ Qββ

Ionization & Scintillation:σ(E)/E = 3.0% @ 570 keV

or 1.4% @ Qββ(a factor of 2 better than the

Gotthard TPC)

Drift Field [kV/cm]0 2 4 6 8 10

%]

σR

es

olu

tio

n [

0

2

4

6

8

10

12Aprile xxxx

Aprile xxxx

Barabash xxxx

Lindblad xxxx

Mel xxxx

Ionization Signal

Correlated Signal

Compilationof Xe resolution

results

EXO ioniz + scint

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

and by now other groups have used this[e.g. E. Aprile et al. PRB 76 (2007) 014115]

EXO-200 will collect 3-4 timesas much scintillation…

further improvement possible

EXO ioniz only


EXO-200 TPC basics


Ultra-low activity Cu vessel

• Very light (~1.5mm thin, ~15kg) to minimize materials

•Different parts e-beam welded together

• Field TIG weld(s) to seal the vessel after assembly (TIG technology tested for radioactivity)

• All machining done by in theCR-shielded HEPL building)


EXO-200 LXe TPC field cage & readout planes

flex cables on back of APD plane

Acrylicsupports

Central HV plane (photo-etched phosphor bronze)

~40cm

QE > 1 at 175nm

Gain set at 100-150V~1500V∆V < ±0.5V ∆T < ±1K APD is the driver

for temperature stabilityLeakage current OK cold

APDs are ideal for ourapplication:

- very clean & light-weight, - very sensitive to VUV

~500 “Bare” LAAPD


EXO-200


BaBa++ Tagging R&DTagging R&D

Vcos(Vcos(ΩΩt) + Ut) + U

UU

Ba ovenBa oven

DC

pote

ntial [V

]DC

pote

ntial [V

]

0 Volts0 Volts

--5 Volts5 Volts

BaBaBuffer gasBuffer gas

CCD

ee-- gungun

Spectroscopy Spectroscopy laserslasers

ScopeScope


Electrode structure being prepared


M.Green et al. arXiv:0702122, Phys Rev A 76 (2007) 023404B.Flatt et al. arXiv:0704.1646, NIM A 578 (2007) 409

~9σ disciminationin 25s integration

First single ion detection in high pressure gas (He, Ar)


Assumptions: Assumptions: 1)1) 80% enrichment in 13680% enrichment in 1362)2) Intrinsic low background + Intrinsic low background + BaBa tagging eliminate all radioactive backgroundtagging eliminate all radioactive background3)3) Energy res only used to separate the 0Energy res only used to separate the 0νν from 2from 2νν modes: modes:

Select 0Select 0νν events in a events in a ±±22σσ interval centered around the 2.481MeV endpointinterval centered around the 2.481MeV endpoint4)4) Use for 2Use for 2νββνββ TT1/21/2>1>1··10102222yr (yr (BernabeiBernabei et al. measurement)et al. measurement)

** σσ(E)/E = 1.4% obtained in EXO R&D, Conti et al Phys Rev B (E)/E = 1.4% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 05420168 (2003) 054201†† σσ(E)/E = 1.0% considered as an aggressive but realistic guess wit(E)/E = 1.0% considered as an aggressive but realistic guess with large lighth large light

collection areacollection area‡‡ Rodin, et. al., Nucl. Phys. A 793 (2007) 213-215# # Caurier, et. al., arXiv:0709.2137v1

EXO neutrino effective mass sensitivityEXO neutrino effective mass sensitivity

Aggressive

Conservative

Case

7.3

33

5.3

24

Majorana mass(meV)

QRPA‡ NSM#

0.7 (use 1)

0.5 (use 1)

2νββBackground(events)

4.1*10281†107010

2*10271.6*5701

T1/20ν(yr,

90%CL)

σE/E @ 2.5MeV

(%)

Run Time(yr)

Eff.(%)

Mass(ton)


The search for neutrinoless double beta decayreally belongs to this tradition!

• Isotope enrichment at an unprecedented scale (for science) is a reality

• 100kg class experiment are also very real

• ton-class experiments are being planned for the near future

ConclusionsOver its glorious history neutrino physics has providedplenty of surprises and has required forays in many different areas of science and technology

Results may, once again, be surprising!


Assumptions: Assumptions: 1)1) 200kg of 200kg of XeXe enriched to 80% in 136enriched to 80% in 1362)2) σσ(E)/E = 1.4% obtained in EXO R&D, Conti et al Phys Rev B 68 (200(E)/E = 1.4% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 0542013) 0542013)3) Low but finite radioactive background: Low but finite radioactive background:

20 events/year in the 20 events/year in the ±±22σσ interval centered around the 2.481MeV endpointinterval centered around the 2.481MeV endpoint4)4) Negligible background from 2Negligible background from 2νββνββ (T(T1/21/2>1>1··10102222yr yr R.BernabeiR.Bernabei et al. measurement)et al. measurement)

EXOEXO--200kg 200kg MajoranaMajorana mass sensitivitymass sensitivity

EXO-200

Case

0.186*0.133†

Majorana mass(eV)

QRPA NSM40

RadioactiveBackground(events)

6.4*10251.6*2700.2

T1/20ν(yr,

90%CL)

σE/E @ 2.5MeV

(%)

Run Time(yr)

Eff.(%)

Mass(ton)

†† Rodin, et. al., Nucl. Phys. A 793 (2007) 213-215* Caurier, et. al., arXiv:0709.2137v1What if What if Klapdor’sKlapdor’s observation is correct ? observation is correct ?

Central value Central value TT1/21/2 ((GeGe) = 1.2) = 1.2+3+3--0.50.5 ··10102525, (, (±±33σσ) ) (Phys. (Phys. LettLett. B 586 (2004) 198. B 586 (2004) 198--212212

consistently use Rodin’s matrix elements for both consistently use Rodin’s matrix elements for both GeGe and and XeXe))

In 200kg EXO, 2yr: In 200kg EXO, 2yr: ••Worst case (QRPA, upper limit) 15 events on top of 40 events Worst case (QRPA, upper limit) 15 events on top of 40 events bkgdbkgd 22σσ

••Best case (NSM, lower limit) 162 events on top of 40 Best case (NSM, lower limit) 162 events on top of 40 bkgdbkgd 1111σσ


Status of 2Status of 2νν mode in mode in 136136XeXe

22νββνββ decay has never been observed in decay has never been observed in 136136Xe. Xe. Some of the lower limits on its half life are close to (and inSome of the lower limits on its half life are close to (and in

one case below) the theoretical expectation.one case below) the theoretical expectation.

=23 k=2.1·1022QRPA (Staudt et al) [T1/2max]

evts/year in the 200kg prototype

(no efficiency applied)T1/2 (yr)

(=0.23 M)(=2.1·1021)NSM (Caurier et al)=0.58 M=8.4·1020QRPA (Vogel et al)

Theoretical prediction1.0·1022Bernabei et al8.1·1020Gavriljuk et al3.6·1020Leuscher et al

Experimental limit

EXOEXO--200 should definitely resolve this issue200 should definitely resolve this issue

neutrinoless double-β...ssi, august 2009 double-beta decay 11 the possibility of neutrinos-less...

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