Z.Djurcic, D.Leonard, A.Piepke Physics Dept, University of Alabama, Tuscaloosa AL

P.Vogel Physics Dept Caltech, Pasadena CA

A. Bellerive, M. Dixit, C. Hargrove, D. Sinclair Carleton University, Ottawa, CanadaW.Fairbank Jr., S.Jeng, K.Hall

Colorado State University, Fort Collins COM.Moe

Physics Dept UC Irvine, Irvine CAD.Akimov, A.Burenkov, M.Danilov, A.Dolgolenko, A.Kovalenko, D.Kovalenko, G.Smirnov, V.Stekhanov

ITEP Moscow, RussiaJ. Farine, D. Hallman, C. Virtue

Laurentian University, CanadaM.Hauger, L.Ounalli, D.Schenker, J-L.Vuilleumier, J-M.Vuilleumier, P.Weber

Physics Dept University of Neuchatel, Neuchatel SwitzerlandM.Breidenbach, R.Conley, C.Hall, A.Odian, C.Prescott, P.Rowson, J.Sevilla, K.Skarpaas, K.Wamba,

SLAC, Menlo Park CAE.Conti, R.DeVoe, G.Gratta, M.Green, T.Koffas, R.Leon, F.LePort, R.Neilson, S.Waldman, J.Wodin

Physics Dept Stanford University, Stanford CA

EEnriched nriched XXenon enon OObservatorybservatoryfor double beta decayfor double beta decay

Double Beta Decay

-

-

1 2 2) : ( , ) ( , ) A Z A Z e e ec

ec

T G E Z MGT1 22 1 2

02 2

/ ,

2

20

2

20

00

102/1

,

mMg

gMZEG

T

FA

VGT

d(n) u(p)

ece

e

W

W

d(n) u(p)

ce

L0

2 0 2) : ( , ) ( , ) A Z A Z e e

e-c

eRW

d(n)

d(n)

u(p)

u(p)

W e-eL

m

N

i

Lej

Lejj UUmm

2

1

L 2

To improve on T120 and <m>: need large source mass

lower background, better event signature

Eee

dN dt

E0

(A,Z)

0+ (A,Z+1)

(A,Z+2)

2+

0+

E0e-e-

Popular candidates

E0 (MeV) Abundance (%)

0.187 4.27148Ca 48Ca76Ge 76Ge 2.040 7.8 82Se 82Kr 2.995 9.2

100Mo 100Ru 3.034 9.6128Te 128Xe 0.868 31.4130Te 130Xe 2.533 34.5136Xe 136Ba 2.479 8.9150Nd 150Sm 3.367 5.6

232Th 232U 238U 238Pu

0.858 1001.145 99.3

dirdirdir, geodirdir, geodir, geodir

melking

dir

Isotopic enrichment for a gaseous substance like Xe is Isotopic enrichment for a gaseous substance like Xe is most economically achieved by ultracentrifugationmost economically achieved by ultracentrifugation

This separation step thatThis separation step thatrejects the light fractionrejects the light fractionis also very effective inis also very effective in

removing removing 8585Kr (TKr (T1/21/2=10.7 yr)=10.7 yr)that is present in the that is present in the

atmosphere from spentatmosphere from spentfuel reprocessingfuel reprocessing

Russia has enoughRussia has enoughproduction production

capacitycapacityto process 100 ton to process 100 ton

Xe and extract Xe and extract up to 10 ton up to 10 ton 136136Xe Xe

in a finite timein a finite time

Nucleus QRPA

Caltech

Shell model

Strasbourg-Madrid

exp

48Ca - 0.91 4.3 x 1019

76Ge 0.71 1.44 1.8 x 1021

82Se 1.5 0.46 8.0 x 1019

100Mo 0.6 - 1.0 x 1019

130Te 0.33 0.35 6.6 x 1020

128Te 0.27 0.25 2.0 X 1024

130Te 0.27 0.29 8.0 x 1020

136Xe <1.0 <2.6 >8.1 x 1020

pex

calc

T

T

2/1

2/1 )(22/1 yrT

pex

calc

T

T

2/1

2/1

direct

direct

geochem.

Enriched Xenon Observatory

for double beta decayAlabama, Caltech, Carleton, Colorado, UC Irvine, ITEP Moscow, Laurentian, Neuchatel, SLAC, Stanford

Ba+Ba+

system best studied (Neuhauser, system best studied (Neuhauser, Hohenstatt, Toshek, Dehmelt 1980)Hohenstatt, Toshek, Dehmelt 1980)Very specific signature “shelving” Very specific signature “shelving” Single ions can be detected from a Single ions can be detected from a photon rate of 10photon rate of 1077/s/s

22PP1/21/2

44DD3/23/2

22SS1/21/2

493nm493nm650nm650nm

metastable 47smetastable 47s

Much improved signature!

136136Xe: Xe: 136136Ba++ e- e- final state can be tagged usingBa++ e- e- final state can be tagged using optical spectroscopy optical spectroscopy (M.Moe PRC44 (1991) 931)(M.Moe PRC44 (1991) 931)

Two detector options under considerationTwo detector options under consideration

High Pressure gas TPCHigh Pressure gas TPC• 5-10 atm, 50 m5-10 atm, 50 m33 modules, modules, 10 modules for 10 t10 modules for 10 t•Xe enclosed in a non-Xe enclosed in a non-structural bagstructural bag• range ~5-10cm: range ~5-10cm: can resolve 2 blobscan resolve 2 blobs•2.5m e-drift at ~250kV2.5m e-drift at ~250kV•Readout Xe scintillation withReadout Xe scintillation with WLSB (T0)WLSB (T0)•Additive gas: quenching and Additive gas: quenching and BaBa++ ++ BaBa+ + neutralizationneutralization•Steer lasers or drift Ba-ion to Steer lasers or drift Ba-ion to detection regiondetection region

Liquid Xe chamberLiquid Xe chamber•Very small detector (3mVery small detector (3m33 for for 10tons)10tons)•Need good E resolutionNeed good E resolution•Position info but blobs not Position info but blobs not resolvedresolved•Readout Xe scintillationReadout Xe scintillation•Can extract Ba from hi-density Can extract Ba from hi-density XeXe•Spectroscopy at low pressure:Spectroscopy at low pressure: 136136Ba (7.8% nat’l) different Ba (7.8% nat’l) different signature from natural Ba signature from natural Ba (71.7% (71.7% 138138Ba)Ba)•No quencher needed, No quencher needed, neutralization neutralization done outside the Xedone outside the Xe

e-, 232Th

(E)/E=3.4 % at 1.59 MeV

(E)/E= 2.7 % at 2.48 MeV

Gotthard 5 bar xenon

(from cathode), 210Po (238U chain)

quenching (/e-)=1/6.5

(E)/E=1.1 % at 2.48 MeV !

Energy resolution

/EF(E/W)E)/E(

F=0.19, W=22 eV

(E)/E=0.13 % at 2.48 MeV !

Light detection (electroluminescence)in xenon (+CF4?)

Doped fibers : 1 step WLS UV (180 +/-20nm) to blue or 2 step WLS with coated fibers

e- track

Optical fibers x-y

Multianode photomultiplier

Grid (metallic cloth)

UV photons

Anode (charge)

Two gap scheme:Grid (metallic cloth)

anode

ITEP-Moscow, Kharkov, Neuchâtel

Fibers (250 m)

1 kV/cm

Found a clear (anti)correlation between ionization and scintillationFound a clear (anti)correlation between ionization and scintillation

~570 keV~570 keV

Major effort now: liquid xenon

Have demonstrated that we can get sufficient energyHave demonstrated that we can get sufficient energyresolution in LXe to separate the 2resolution in LXe to separate the 2νν from the 0from the 0νν modesmodes

We can do ionization measurements

as well as anyone

Now we turn on our newcorrelation technique…

Resolu

tions

Resolu

tions

at 5

70 keV

at 5

70 keV

3.3%@570keV3.3%@570keVor 1.6%@2.5MeVor 1.6%@2.5MeV

Fishing ions in LXeFishing ions in LXe

Initial Ra/Th ionInitial Ra/Th iongrabbing successfulgrabbing successful

As expected release from aAs expected release from afinite size metallic tip finite size metallic tip

is challengingis challenging

214214Po (164ms)Po (164ms)

230230U (20.8d)U (20.8d)

222222Ra (38s)Ra (38s)

210210Pb (22yr)Pb (22yr)

226226Th (30.5min)Th (30.5min)

218218Rn (35ms)Rn (35ms)

5.99MeV5.99MeV

6.45MeV6.45MeV

6.68MeV6.68MeV

7.26MeV7.26MeV

7.83MeV7.83MeV

αα

230230U source U source αα spectrum spectrumas delivered by LLNLas delivered by LLNL

and measured in vacuumand measured in vacuum

αα spectrum fromspectrum fromwhatever is grabbedwhatever is grabbed

by the tipby the tip(in Xe atmosphere)(in Xe atmosphere)

αα

αα

αα

αα

Ion Trap R&D at UHV/atmospheric pressure

RF quadrupole trap RF quadrupole trap loaded in UHV from loaded in UHV from

a Ba dispensera Ba dispenserand e-beam ionizerand e-beam ionizer

Xe can be injected Xe can be injected while observing while observing

the ionsthe ions

CCD Image of Ba+ ions in the trap

Trapedge

Indeed we are talking about single ions: one can load the trapIndeed we are talking about single ions: one can load the trapwith multiple ions and then observe the signal intensity as ionswith multiple ions and then observe the signal intensity as ions

are dropped one by one…are dropped one by one…

Zero ion backgroundZero ion background

All above in UHV;Perform the sameexperiment in noblegas atmosphere

In parallel, build liquid TPC prototype, without Ba tagging

• Prototype Scale:– 200 Kg enriched 136Xe– All functionality of EXO except Ba identification– Operate in WIPP for ~two years

• Prototype Goals:– Test all technical aspects of EXO (except Ba id)– Measure 2 mode– Set decent limit for 0 mode (probe Heidelberg-

Moscow)

Massive materials qualification programled by Alabama with contributions from

Carleton, Laurentian and Neuchatel

•Approximate detector simulation with material properties to establish target activities•NAA whenever possible (MIT reactor + Alabama)•Direct Ge counting at Neuchatel, Alabama and soon Canada•High sensitivity mass spectroscopy starting in Canada•Alpha counting at Carleton and Stanford•Rn outgassing measurements starter at Laurentian (Xe plumbing)•Full detector simulation in progress

Detector

(356 on each side, 16 mm diameter 120 % QE in UV))

Teflon vessel

APD plane below crossed wire array

100 APD channels (7 APD grouped together) provide light and t0

200 ionization channels (groups of wires 100 x +100 y)

Can define fiducial volume

Cryostat Cross Section

Condenser

Xenon Heater

should be

on this area

Xenon

Chamber

Outer Copper Vessel

Inner Copper Vessel

FC-87

FC-87

1” thick Thermal Insulation (MLI-vacuum), not shown to scale

Outer Door

Inner Door

Xenon

Chamber

Support

Full detector viewWith Pb shielding

DoE’s Waste Isolation Pilot Plant (WIPP), Carlsbad NM

Status

• Enriched Xe in hand.

• Clean room installed at Stanford.

• WIPP agreement, including Environmental Impact, complete.

• Cryostat being designed.

• Xe purification and refrigeration issues being finalized

• Detector vessel, readout, and electronics being engineered.

200 kg prototype, estimated sensitivity, without Ba tagging

Estimate background from radioactivity (2 negligible)

Mass

(kg)

Enrichment

(%)

Eff.

(%)

/E@2.5MeV

(%)

Time

(yr)

Background

(events)

T1/20

(yr)

<m>(eV)

RQRPA

200 80 70 1.6 2 40 6.4*1025 0.28

V. A. Rodin et al. Phys.Rev. C68 (2003) 044302

Ultimate sensitivity, assuming

1) that the Xe chamber + Ba tagging gives 0 background from radioactivity...2) that the energy resolution is (E)/E=2 % (2background!)

Conclusion:

With a coordinated effort, the meV region is within reach!

Mass

(kg)

Enrichment

(%)

Eff.

(%)

/E@2.5MeV

(%)

Time

(yr)

Background

(events)

T1/20

(yr)

<m>(eV)

RQRPA

1000

10000

80

80

70

70

1.6

1.0

5

10

0.5 (use 1)

0.7 (use 1)

2.0*1027

4.1*1028

0.05

0.01