A search for neutrinoless double beta decay with xenonA search for neutrinoless double beta decay with xenon

M. BreidenbachSLUO

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EXO CollaborationH.Breuer, C.Hall, L.Kaufman, D.Leonard, S.Slutsky,

K.Barry, E.Niner, A.PiepkePhysics Dept., U. of Alabama, Tuscaloosa AL, USAP.Vogel Physics Dept., Caltech, Pasadena CA, USA

Y-R.YenU. of Maryland, College Park MD, USAK.Kumar, A.Pocar U. of Massachusetts, Amherst, Amherst MA, USA M.Auger, G.Giroux, R.Gornea, F.Juget, G.Lutter, J-y p

A.Bellerive, M.Bowcock, M.Dixit, K.Graham, C.Hargrove, E.Rollin, D.Sinclair, V.StricklandCarleton University, Ottawa, CanadaC.Benitez-Medina, S.Cook, W.Fairbank Jr., K.Hall, B Mong

M.Auger, G.Giroux, R.Gornea, F.Juget, G.Lutter, JL.VuilleumierLaboratory for High Energy Physics, Bern, SwitzerlandN.Ackerman, M.Breidenbach, R.Conley, W.Craddock, S H i J H d s D M k A Odi B.Mong

Colorado State U., Fort Collins CO, USAM.Moe Physics Dept., UC Irvine, Irvine CA, USAD.Akimov, I.Alexandrov, A.Burenkov, M.Danilov,

l l k l l k

S.Herrin, J.Hodgson, D.Mackay, A.Odian, C.Prescott, P.Rowson, K.Skarpaas, J.Wodin, L.Yang, S.ZalogSLAC, Menlo Park CA, USAL.Bartoszek, R.Cooper, R.DeVoe, M.Dolinski, B.Flatt,

A.Dolgolenko, A.Karelin, A.Kovalenko,A.Kuchenkov, V.Stekhanov, O.ZeldovichITEP Moscow, RussiaB.Aharmin, K.Donato, J.Farine, D.Hallman, U.WichoskiLaurentian U., Canada

, p , , , ,G.Gratta, M.Green, F.LePort, M.Montero-Diez, R.Neilson, A.Reimer-Muller, A.Rivas, K.O'Sullivan, K.TwelkerPhysics Dept., Stanford University, Stanford CA USALaurentian U., Canada USA

2PASCOS 2009 Jesse Wodin, SLAC 2

ββ Decay0 m d :

2ν:

0ν mode:

A hypothetical process that can happen only if:

Conventional 2nd order process in nuclear physics

Mν ≠ 0;

ν = ν;

│∆L│=2│∆L│=2

│∆(B-L)│=2

Current knowledge of the neutrinomass hierarchy

2 8 V

T

23 eV

5 2

~2.8 eV

From tr

(Maintz~0.3 eV

~1 eV

Time of fligh

(PDG

Solar ~ 7·10-5 eV2

ritium endpo

z and Troits

From 0nbb

From W

M

ht from SN

19G 2002)

Atmospheric~ 2·10-3 eV2

Atmospheric~ 2 10-3 eV2

Solar ~ 7·10-5 eV2

intk)

bif n

is Majo

MA

P

987A

~ 2·10 3 eV2

rana

Normalhierarchy

Invertedhierarchy

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hierarchy hierarchyMohapatra et al., arxiv:hep-ph/0412099v2 (2004)

EXO Sensitivities

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Experimental ββ observables

0νββ peak,Normalized to 10-6, 5% FWHM

2νββ spectrum, normalized to 1 0νββ peak,

Energy resolution is the only tool to separate 2νββfrom 0νββ

ee-- ee--

normalized to 1 ββ p a ,Normalized to 0.01, 5% FWHM

from 0νββ

Elliot, S. et al., Annu. Rev. N l P t S i 2002

136136XeXe 136136BaBa++++

Nucl. Part. Sci. 2002. 52:115–51

Background control is critical. Ba tagging changes

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EXO to a coincidence experiment – eliminating external backgrounds.

Sensitivity

ε is efficiencya is isotopic abundancea MT⎡ ⎤ 1/ 2A is atomic massM is source massT is timeB is background

S1/ 20ν ∝ε a

AMTBΓ

⎡ ⎣ ⎢

⎤ ⎦ ⎥

Γ is resolution

To maximize sensitivity:•Large mass more signal•Large mass – more signal•Low background – the biggest challenge by far!!!•High detection efficiency - sure•Good energy resolution required to separate 0νββ from 2νββ•Good energy resolution – required to separate 0νββ from 2νββ

Identification of the daughter isotope rejects all but 2νββ background and confirm double beta decay.

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conf rm double beta decay.

Multiple Paths to a Background Free Detector

EXOEXO

High Pressure

Cryogenic Liquid TPCPressure

Gas TPCLiquid TPC

Ba Identification in High-Pressure Gas

Ba Identification in Liquid

Ba Identification in low-pressure Gas

“EXO is a program aimed at building an enriched xenon double beta decay experiment with a one or more ton 136Xe source with the particular ability experiment with a one or more ton Xe source, with the particular ability to detect the two electrons emitted in the decay in coincidence with the positive identification of the 136Ba daughter via optical spectroscopy”

EXO Strategy:

•Separately develop an understanding of the issues for understanding of the issues for liquid Xe and for moderate pressure gaseous Xe.

F b h d l •For both cases, develop techniques for extraction and tagging of the Ba ion.

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What, Where & Who,EXO-200:

200 Kg enriched 136Xe liquid TPC at WIPP.All features (including all issues of radio purity) except Ba+ tagAll features (including all issues of radio purity) except Ba tag.Conceived as a prototype, actually a non-trivial experiment.

Spectroscopic identification of single Ba+

Operational with RF trap at StanfordOperational with RF trap at Stanford.Extraction techniques

Unsolved, work primarily at Stanford, Colorado, SLACVarious tips that electrostatically attract the ion and then release to trap.p y p

Gas TPC100 Kg system (not radio quiet) at Carleton, LaurentianCarry ion to trap through system of nozzles and differential pumping

EXO is an international collaboration of 74 people – senior physicists, post-docs, grad students, engineers, and techs. We are interested in modest expansion with talented experimentalists.

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Why Xenon?

Xenon isotopic enrichment is easier: Xe is a gas and 136Xe is the heaviest isotope.

Xenon is “reusable”: can be re-purified and recycled into new detector (no crystal growth).

Monolithic detector: LXe is self shielding surface contamination minimized Monolithic detector: LXe is self shielding, surface contamination minimized.

Minimal cosmogenic activation: no long lived radioactive isotopes of Xe.

Energy resolution in LXe can be improved: scintillation light + ionizationanti-correlation.

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

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EXO-200 Goals

-Look for 0νββ decay of 136Xe with competitive sensitivity: 0.13 ev (NSM)(1) ; 0.19 ev (QRPA)(2)

(T0ν > 6 x 1025 y current limit: T0ν > 1 2 x 1024 y) (T0ν1/2 > 6 x 1025 y, current limit: T0ν

1/2 > 1.2 x 1024 y)

M th t d d 2 ββ d f 136X (Q 2457 8 ± 0 4 k V) d

(1) Rodin et al., Nucl. Phys. A 793 (2007) 213-215(2) Caurier et al., arXiv:0709.2137v1

•Measure the standard 2νββ decay of 136Xe (Q = 2457.8 ± 0.4 keV) andmeasure its lifetime (best upper limit to date: T2ν

1/2 > 1 x 1022 y[R. Bernabei et al., Phys. Lett. B 546 (2002) 23]

•Measure backgrounds on a significant size ultra-clean detector to understand the additional advantage of the Ba tag.

•Measure backgrounds at ~2000 m w e depth•Measure backgrounds at ~2000 m.w.e. depth•Test LXe technology (purification, control, and enrichment on a large scale)•Test liquid TPC strategy, position and energy

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EXO-200

Avalanche photodiodes (scintillation light collection)e‐

e‐e‐

ee‐

Ionization Scintillation

e‐

e‐e‐ e‐

e‐

e‐

e‐ e‐

0νββ decay daughter (136Ba++)

Ionized/excited Xe

-75kVCharge collection

e‐

00k 136 ( 0% h ) l d h ( 160 ) b h d d

e‐ 0νββ ionization trail e‐

• 200kg 136Xe (80% enrichment) liquid phase (~160K), both source and detector of 0νββ• ~ 2.5 MeV 0νββ endpoint energy•0νββ electrons deposit energy as charge (slow) and scintillation (fast)

ll h l f

QββXe−136

• Collect ionization on wires -> charge preamplifiers• Collect scintillation on APDs• Energy reconstruction from ionization + scintillation (∆E/E = 1.4% at Qbb)• Event position from charge distribution and tSCINT-tION (useful for Ba tagging

f ll E )

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on full EXO)

LXe Data Show Anticorrelation between Scintillation and Ionization

•Timing of the event:Scintillation light givest = 0 for drift time (z)

~570 keV~570 keVBi-207 source

1 kV/cm

t 0 for drift time (z)•Position of the event:

Crossed wires at the anode (x-y) collect charge at t=z•Event energy: Event energy:

Ionization + scintillationlight

I i ti l Ionization alone: σ(E)/E = 3.8% @ 570 keV or 1.8% @ Q(ββ)�

Ionization & Scintillation:

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σ(E)/E = 3.0% @ 570 keV or 1.4% @ Q(ββ)E.Conti et al., Phys. Rev. B: 68 054201 (2003)

acrylic supports

LAAPD plane (copper) and x-y wires (photo-etched phosphor bronze)

TPC Design

teflon light reflectorsCentral HV plane (photo-etched

phosphor bronze)

field shaping rings (copper)

flex cables on back of flex cables on back of APD plane (copper on

kapton, no glue)

x-y crossed wires, 60o

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EXO-200

~1.5mCopper cryostat

~1.5mCopper liquid xenon vessel . m

HFE7000cooling/shielding fluid

16Surrounded by 25 cm Pb shield

Looking into EXO-200 detector without APDs

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Detector after cable and APD installation, before final endcap welding

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EXO-200 installation site: WIPP

• EXO‐200 installed at WIPP (Waste Isolation Pilot Plant), in Carlsbad, NM

600 fl b d (2 0

EXO‐200 location

• 1600 mwe flat overburden (2150 feet, 650 m)• U.S. DOE salt mine for low‐level radioactive waste storageg• Salt “rock” low activity relative to hard‐rock mine

EXO area at WIPP, before installation 

Φμ ~ 1.5 ×105 yr−1m−2sr−1

U ~ 0.048ppmTh 0 25

(2007)

Th ~ 0.25ppmK ~ 480ppm

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Esch et al., arxiv:astro‐ph/0408486 (2004)

EXO-200 facility at WIPP

Cryostat, Pb shielding, and xenon transfer lines installed at WIPP in EXO cleanrooms for 4/2009 cryogenic commissioning

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cryogenic commissioning.

Centrifugally Enriched 136Xe

200 kg of xenon enriched to 80% = 160 kg of 136Xe:The most isotope in possession by any ββ0ν collaboration

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The most isotope in possession by any ββ0ν collaboration

Ba+ Tagging Schematic for Liquid Phase EXO

Quadrupole linear ion trap

Ba+ grabber

p

APDs Grid plane

e-e-

e-

e- e-

CCDe-

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Single Ba+ ion detection

Daughter identified by optical spectroscopy of Ba+, well studied in ion traps for more than 25 years [Neuhauser, Hohenstatt, Toshek,

h l h ( ) Dehmelt, Phys. Rev. A 22 (1980) 1137]

s ifi si t 2P1/2: ~7.9ns

Ba+

- very specific signature (“Λ” shelving)

cycling 493/650 nm transitions 493nm 650nm

- cycling 493/650 nm transitions gives a fluorescence rate of ~108 Hz (in vacuum)

2D :

plenty of light! 2

2D3/2: metastable

~83s

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plenty of light! 2S1/2

Single Ba+ tagging in a quadrupole ion trap

Ba ovenCCD

Spectroscopy lasers

ScopeScope

pote

ntia

l [V

]

0 Volts

Ba

e- gun

DC

-5 VoltsBuffer gas

• Observed LIF of a single Ba+ in a buffer gas filled

M Green et al Phys Rev A 76 (2007) 023404

• Observed LIF of a single Ba+ in a buffer gas filled ion trap (~ 10‐3 torr He, some Xe)• ~ 9σ observation at 25s storage time

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

Liquid Phase Extraction

C i P bAu-coated leads

Vespel Resonant Ion Spectroscopy

Cryogenic Probe

sensorVespel sleeves

2mmRead-out cables

Cu cold finger

W heater W heater wire

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EXO gas phase R&D

• Several gas-phase advantages

• Improved DE/E• Tracking• In-situ ID of Ba?

• Gas-phase R&D underway at Laurentian and Gotthard O GX at Laurentian and Gotthard (U. Bern)

One GXe concept

• 10 bar GXe chamber• 1 MeV e- source• 1 MeV e- source• Segmented readout (tracking)• CsI photocathode

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Ba extraction test setup

p

SLAC ContextL nt t

As accelerator based particle physics opportunities at p p y ppSLAC (on site) have gone, the lab appears interested in playing a stronger role in national underground physics.

SLAC h s inv lvement ith EXO nd CDMS b th h ve SLAC has involvement with EXO and CDMS, both have interests at DUSEL and SNOLab.

EXO has an S4 cooperative agreement to provide EXO has an S4 cooperative agreement to provide university support for a full EXO proposal and needed R&D

L h d f ff SLAC has committed to a significant engineering effort to complement the NSF S4 support.

The primary focus of SLAC is EXO-200

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The primary focus of SLAC is EXO-200.