session14 farine r1 -

EXO-200 ResultsJacques Farine, Laurentian University

For the EXO collaboration

Neutrino-12 Kyoto 6 June 2012

The EXO collaboration

University of Alabama, Tuscaloosa AL, USAD. Auty, M. Hughes, R. MacLellan, A. Piepke, K. Pushkin, M. Volk

University of Bern, SwitzerlandM. Auger, S. Delaquis, D. Franco, G. Giroux, R. Gornea, T. Tolba, J-‐L. Vuilleumier, M. Weber

California InsQtute of Technology, Pasadena CA, USA -‐ P. Vogel

Carleton University, OSawa ON, CanadaA. Coppens, M. Dunford, K. Graham, C. Hägemann, C. Hargrove, F. Leonard, C. Oullet, E. Rollin, D. Sinclair, V. Strickland

Colorado State University, Fort Collins CO, USAS. Alton, C. Benitez-‐Medina, C. Chambers, Adam CraycraW, S. Cook, W. Fairbank, Jr., K. Hall, N. Kaufold, T. Walton

University of MassachuseSs, Amherst MA, USAT. Daniels, S. Johnston, K. Kumar, A. Pocar, J.D. Wright

University of Seoul, South Korea -‐ D. Leonard

SLAC NaQonal Accelerator Laboratory, Menlo Park CA, USAM. Breidenbach, R. Conley, R. Herbst, S. Herrin, J. Hodgson, A. Johnson, D. Mackay, A. Odian, C.Y. PrescoS, P.C. Rowson, J.J. Russell, K. Skarpaas, M. SwiW, A. Waite, M. WiSgen, J. Wodin

Stanford University, Stanford CA, USAP.S. Barbeau, T. Brunner, J. Davis, R. DeVoe, M.J. Dolinski, G. GraSa, M. Montero-‐Díez, A.R. Müller, R. Neilson, I. Ostrovskiy, K. O’Sullivan, A. Rivas, A. Sabourov, D. Tosi, K. Twelker

Technical University of Munich, Garching, GermanyW. Feldmeier, P. Fierlinger, M. Marino

University of Illinois, Urbana-‐Champaign IL, USA -‐ D. Beck, J. Walton, L. Yang

Indiana University, Bloomington IN, USA -‐ T. Johnson, L.J. Kaufman

University of California, Irvine, Irvine CA, USA -‐ M. Moe

ITEP Moscow, Russia -‐ D. Akimov, I. Alexandrov, V. Belov, A. Burenkov, M. Danilov, A. Dolgolenko, A. Karelin, A. Kovalenko, A. Kuchenkov, V. Stekhanov, O. Zeldovich

LaurenQan University, Sudbury ON, CanadaE. Beauchamp, D. Chauhan, B. Cleveland, J. Farine, B. Mong, U. Wichoski

University of Maryland, College Park MD, USAC. Davis, A. Dobi, C. Hall, S. Slutsky, Y-‐R. Yen

2

3

The EXO-200 TPC

• Field shaping rings: copper

• Supports: acrylic

• Light reflectors/diffusers: Teflon

• APD support plane: copper; Au (Al) coated for contact (light reflection)

• Central cathode, U+V wires: photo-etched phosphor bronze

• Flex cables for bias/readout: copper on kapton, no glue

Comprehensive material screening program

Goal: 40 cnts/2y in 0νββ ±2σ ROI, 140 kg LXe

• 38 U triplet wire channels (charge)

• 38 V triplet wire channels, crossed at 60o (induction)

• 234 large area avalanche photodiodes (APDs, light in groups of 7)

• Wire pitch 3 mm (9 mm per channel)

• Wire planes 6 mm apart and 6 mm from APD plane

• All signals digitized at 1 MS/s, ±1024S around trigger

• Drift field 376 V/cm

40 cm40 cm

Two almost identical halves reading ionization and 178 nm scintillation, each with:

x

z

y

4

EXO-200 detector: JINST 7 (2012) P05010Characterization of APDs: NIM A608 68-75 (2009)Materials screening: NIM A591, 490-509 (2008)

Copper vessel 1.37 mm thick175 kg LXe, 80.6% enr. in 136XeCopper conduits (6) for:• APD bias and readout cables• U+V wires bias and readout• LXe supply and returnEpoxy feedthroughs at cold and warm doorsDedicated HV bias line

4

EXO-200 detector: JINST 7 (2012) P05010Characterization of APDs: NIM A608 68-75 (2009)Materials screening: NIM A591, 490-509 (2008)

5

The EXO-200 Detector

VETO PANELS

DOUBLE-WALLED

CRYOSTAT

LXe VESSEL

LEAD SHIELDING

JACK AND FOOT

VACUUM PUMPS

FRONT END

ELECTRONICS

HV FILTER AND

FEEDTHROUGH

> 25 cm

25 mm ea

High purity Heat transfer fluidHFE7000 > 50 cm

1.37 mm

VETO PANELS

5

The EXO-200 Detector

Muon veto• 50 mm thick plastic scintillator panels• surrounding TPC on four sides.• 95.5 ± 0.6 % efficiencyVeto cuts (8.6% combined dead time)• 25 ms after muon veto hit • 60 s after muon track in TPC• 1 s after every TPC event

Sep 2011 – Hardware upgrades• APD gain increase by factor 2• improved U-wire shaping • added outer lead shield

Purity

Xenon gas is forced through heated Zr getter by custom ultraclean pump.Electron lifetime τe is determined by measuring the attenuation of the ionization signal as a function of drift time for the full-absorption peak of gamma ray sourcesFor this analysis, the recirculation rate was increased to 14 slpm, leading to long electron lifetimes in the TPC

At τe = 3 ms:• max. drift time ~110 µs• loss of charge is 3.6% at full

drift length

Data taking phases and Xenon Purity

Run I~250 μs

This analysis This analysis

7

Ultraclean pump: Rev Sci Instrum. 82(10):105114 Xenon purity with mas spectroscopy: NIM A675 (2012) 40-46Gas purity monitors: NIM A659 (2011) 215-228

Run I Run 2 (this analysis)

Period May 21, 11 – Jul 9, 11 Sep 22, 11 – Apr 15,12

Live Time 752.7 hr 2,896.6 hr

Exposure (136Xe) 4.4 kg-yr 26.3 kg-yr

Publ. PRL 107 (2011) 212501 arXiv:1205:5608

2011-07-12 2011-09-01 2011-11-01 2011-12-31 2011-03-01

Sep 2011 – Hardware upgrades• APD gain increase by factor 2• improved U-wire shaping • added outer lead shield

Purity

Xenon gas is forced through heated Zr getter by custom ultraclean pump.Electron lifetime τe is determined by measuring the attenuation of the ionization signal as a function of drift time for the full-absorption peak of gamma ray sourcesFor this analysis, the recirculation rate was increased to 14 slpm, leading to long electron lifetimes in the TPC

At τe = 3 ms:• max. drift time ~110 µs• loss of charge is 3.6% at full

drift length

Data taking phases and Xenon Purity

Run I~250 μs

This analysis This analysis

7

Ultraclean pump: Rev Sci Instrum. 82(10):105114 Xenon purity with mas spectroscopy: NIM A675 (2012) 40-46Gas purity monitors: NIM A659 (2011) 215-228

Run I Run 2 (this analysis)

Period May 21, 11 – Jul 9, 11 Sep 22, 11 – Apr 15,12

Live Time 752.7 hr 2,896.6 hr

Exposure (136Xe) 4.4 kg-yr 26.3 kg-yr

Publ. PRL 107 (2011) 212501 arXiv:1205:5608

2011-07-12 2011-09-01 2011-11-01 2011-12-31 2011-03-01

Run I Results:

T1/22νββ (136Xe) = (2.11 ± 0.04 stat ± 0.21 sys)·1021 yr

In disagreement with previously reported limits by

R. Bernabei et al. Phys. Lett. B 546 (2002) 23, andYu. M. Gavriljuk et al. , Phys. Atom Nucl. 69 (2006)

This was also a measurement of a nuclear matrix element of 0.019 MeV-1, the smallest measured among the 2νββ emitters

0.7 mm dia.epoxy coated

CalibrationsSource Weak (kBq) Strong (kBq)

60-‐Co 3.0 15.0

137-‐Cs 0.5 7.2

228-‐Th 1.5 38.0

Stainless steelcapsule

6m long, lowfriction cable

Miniaturized sources

8

x

zy

weak 228Th

Provide 4 full energy deposition peaks in the

energy range662 keV – 2615 keV

Event reconstruction

• Signal finding – matched filters applied on U, V and APDs waveforms

• Signal parameter estimation (t, E) for charge and light

• Cluster finding – assignment to Single Site (SS) or Multiple Site (MS): resolution 18mm in X and Y and 6 mm in Z

Amplitudes corrected by channel for gain variationRequire events to be fully reconstructed in 3D

Reconstruction efficiency for 0νββ is 71% – estimated by MC and verified by comparing the 2νββ MC efficiency with low background data, over a broad range in energy

9

Combining Ionization and Scintillation

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

cutting this region removes α particles and events with imperfect charge collection

228Th sourceSS

QββRotation angle chosen to optimize energy resolution at 2615 keV

Properties of xenon cause increased scintillation to be associated with decreased ionization (and vice-versa)

Scintillation: 6.8%Ionization: 3.4%Rotated: 1.6%(at 2615 keV gamma line)

Use projection onto a rotated axis to determine event energyQββ

10

Source Data/MC Agreement

Multi site (MS) and single site (SS) data (black points) are compared to model (blue curve)

Single site fraction agrees to within 8.5% Source activities measured to within 9.4%

coun

ts /2

0keV

0200400600800

1000120014001600180020002200

MS

energy (keV)1000 1500 2000 2500 3000 3500

coun

ts /2

0keV

0

100

200

300

400

500 SS

11

cou

nts

/ 2

0k

eV

0

100

200

300

400

500 MS

energy (keV)1000 1500 2000 2500 3000

cou

nts

/ 2

0k

eV

0

50

100

150

200

250SS

228Th 60Co

Calibrations

12

Using quadratic model for energy calibration, single- and multi-site residual are < 0.1%

Energy resolution model:

Resolution dominated by constant (noise) term p1

At Qββ (2458 keV):σ/Ε = 1.67 % (SS)σ/Ε = 1.84 % (MS)

σ2

Tot = p2

0E + p2

1 + p2

2E2

MS

SS

214Bi – 214Po correlations in the EXO-200 detector

Rn Content in Xenon

13

Using the Bi-Po (Rn daughter) coincidence technique, we can estimate the Rn content in our detector. The 214Bi decay rate is consistent with measurements from alpha-spectroscopy.

β-‐decay

α-‐decay

ScinQllaQon

IonizaQon

Total 222Rn in LXe after initial fill

Long-‐term study shows a constant source of 222Rn dissolving in enrLXe: 360 ± 65 μBq (Fid. vol.)

14

Low Background 2D SS Spectrum

Events removed by diagonal cut:• alpha events (they leave large ionization density, which leads to more recombination, which

means more scintillation light)• events near edge of detector, where not all the charge ends up on the collection wires

208Tl linecut region

α

zoomed-out

coun

ts /2

0keV

-210

-110

1

10

210

310 MS

energy (keV)1000 1500 2000 2500 3000 3500

coun

ts /2

0keV

-210

-110

1

10

210

310 SS

15

Low Background SpectrumMaximum likelihood fit

Trigger fully efficientabove 700 keV

Low backgroundrun livetime:120.7 days

Active mass: 98.5 kg LXe

(79.4 kg 136LXe)

Exposure 32.5 kg.yr

Total dead time from vetos: 8.6%

Various background PDFs fitted along with 2νββ and 0νββ PDFs

2 (90% CL Limit)0

K LXe Vessel40

Mn LXe Vessel54

Co LXe Vessel60

Zn LXe Vessel65

Th LXe Vessel232

U LXe Vessel238

Xe Active LXe135

Rn Active LXe222

Rn Inactive LXe222

Bi Cathode Surface214

Rn Air Gap222

DataTotal

Overflow bin

No events inoverflow bin

coun

ts /2

0keV

-210

-110

1

10

210

310 MS

energy (keV)1000 1500 2000 2500 3000 3500

coun

ts /2

0keV

-210

-110

1

10

210

310 SS

15





(79.4 kg 136LXe)

Exposure 32.5 kg.yr



2 (90% CL Limit)0

K LXe Vessel40

Mn LXe Vessel54

Co LXe Vessel60

Zn LXe Vessel65

Th LXe Vessel232

U LXe Vessel238

Xe Active LXe135

Rn Active LXe222

Rn Inactive LXe222


Rn Air Gap222

DataTotal

Overflow bin


~22,000 2νββ events !Also populate MS

spectrum, partly due to bremsstrahlung

MC predicts that 82.5% of 2νββ are SS

coun

ts /2

0keV

-210

-110

1

10

210

310 MS

energy (keV)1000 1500 2000 2500 3000 3500

coun

ts /2

0keV

-210

-110

1

10

210

310 SS

15





(79.4 kg 136LXe)

Exposure 32.5 kg.yr



2 (90% CL Limit)0

K LXe Vessel40

Mn LXe Vessel54

Co LXe Vessel60

Zn LXe Vessel65

Th LXe Vessel232

U LXe Vessel238

Xe Active LXe135

Rn Active LXe222

Rn Inactive LXe222


Rn Air Gap222

DataTotal

Overflow bin


T1/22νββ (136Xe) = (2.23 ± 0.017 stat ± 0.22 sys)·1021 yr

In agreement with previously reported value by

EXO-200 Phys.Rev.Lett. 107 (2011) 212501

and

KamLAND-ZEN Phys.Rev.C85:045504,2012)

coun

ts /2

0keV

0

5

10

15

20

25

30

35MS

energy (keV)2000 2200 2400 2600 2800 3000 3200

coun

ts /2

0keV

0

2

4

6

8

SS1σ 2σ

RO

I16

Zoomed around 0νββ region of interest (ROI) Low Background Spectrum 2

(90% CL Limit)0K LXe Vessel40

Mn LXe Vessel54

Co LXe Vessel60

Zn LXe Vessel65

Th LXe Vessel232

U LXe Vessel238

Xe Active LXe135

Rn Active LXe222

Rn Inactive LXe222


Rn Air Gap222

DataTotal

Constraints:• SS to MS ratio

within ±8.5% of values predicted by MC (set by largest variations in source data)

• other systematic uncertainties

Profile likelihood fit to entire SS and MS spectra to extract limits for T1/20νββ

No 0ν signal observed

Background counts in ±1,2 σ ROI

17

Expected events from fitExpected events from fitExpected events from fitExpected events from fit

±1 σ±1 σ ±2 σ±2 σ222Rn in cryostat air-gap 1.9 ±0.2 2.9 ±0.3238U in LXe Vessel 0.9 ±0.2 1.3 ±0.3232Th in LXe Vessel 0.9 ±0.1 2.9 ±0.3214Bi on Cathode 0.2 ±0.01 0.3 ±0.02

All Others ~0.2 ~0.2

Total 4.1 ±0.3 7.5 ±0.5

Observed 11 55

Background index b (kg-1yr-1keV-1) 1.5·10-3 ± 0.11.5·10-3 ± 0.1 1.4·10-3 ± 0.11.4·10-3 ± 0.1

ROI

2 (90% CL Limit)0

K LXe Vessel40

Mn LXe Vessel54

Co LXe Vessel60

Zn LXe Vessel65

Th LXe Vessel232

U LXe Vessel238

Xe Active LXe135

Rn Active LXe222

Rn Inactive LXe222


Rn Air Gap222

DataTotal

EXO-200 goal (slide 3):

40 cnts/2y in ±2σ ROI, 140 kg LXe

In this data 120 days, 98.5 kg, this would be: 4.6

Expected from the fit: 7.5

Observed: 5Background within

expectation

18

Limits on T1/20νββ and〈mββ〉

From profile likelihood:

T1/20νββ > 1.6·1025 yr

〈mββ〉< 140–380 meV .(90% C.L.)

arXiv:1205.5608 – Subm. to PRL

H.V. Klapdor-Kleingrothaus and I.V. Krivosheina, Mod. Phys. Lett., A21 (2006) 1547.

A. Gando et al. Phys. Rev. C 85 (2012) 045504

Xe (yr)136 1/2T2410 2510 2610

2410

2510

2610

68%

CL

EXO

-200

(thi

s wor

k)

90%

CL

Kam

LAN

D-Z

EN 9

0% C

L

RQRPA-1

QRPA-2

IBM-2

GCM

NSM

KK&K 68% CL

Heidelberg-Moscow90% CL

0.2

0.3

0.4

0.5

0.6

0.70.8

0.9

0.2

0.3

0.4

0.5

0.6

0.7

0.2

0.3

0.4

0.5

0.3

0.4

0.5

0.6

0.70.8

0.91

0.2

0.3

0.4

0.5

0.6

0.70.8

0.91

Ge (

yr)

76 1/

2T

2410

2510

2610

H.V. Klapdor-Kleingrothaus et.al. Eur. Phys. J. A12 (2001) 147

Interpret as lepton number violating process with effective

Marojana mass〈mββ〉:

(

T0νββ1/2

)

−1= G

0ν∣

∣Mnucl

∣

∣

2〈mββ〉

2

Systematics and sensitivity

Error breakout: expected 90% CL limit given absolute knowledge (0 error) of a given parameter or set of parameters

19

Distribution of 0νββ T1/2 90% CL

Upper limits from Monte Carlo

From estimated background, expect to quote a 90% CL upper limit on T1/2 :≥ 1.6 x 1025 yr 6.5% of the time≥ 7 x 1024 yr 50% of the time

Term %

Fiducial Volume 12.34

β scale 9.32

SS / (SS + MS) 0.93232Th LXe Vessel 0.11238U LXe Vessel 0.04222Rn Air Gap 0.04

Calibration offsets 0.04

SummaryEXO-200 is taking low background dataDetector working well, met our goals: Energy resolution: 1.67% at Qββ

Background: 1.5 x 10-3 kg-1keV-1yr-1

1 (5) counts in 1σ (2σ) 0νββ ROI

Improvements on σ and b in progressEXO-200 approved to run for 4 more years

20

Xe (yr)136 1/2T2410 2510 2610

2410

2510

2610

68%

CL

EXO

-200

(thi

s wor

k)

90%

CL

Kam

LAN

D-Z

EN 9

0% C

L

RQRPA-1

QRPA-2

IBM-2

GCM

NSM

KK&K 68% CL

Heidelberg-Moscow90% CL

0.2

0.3

0.4

0.5

0.6

0.70.8

0.9

0.2

0.3

0.4

0.5

0.6

0.7

0.2

0.3

0.4

0.5

0.3

0.4

0.5

0.6

0.70.8

0.91

0.2

0.3

0.4

0.5

0.6

0.70.8

0.91

Ge

(yr)

76 1/

2T

2410

2510

2610

T1/20νββ > 1.6·1025 yr

〈mββ〉< 140–380 meV .(90% C.L.)

arXiv:1205.5608 – Subm. to PRL

Extra slides

Spatial distributions

22

• 2νββ rate does not change with fiducial volume• Background gammas rates drop towards the inside of

the detector• Events in the ±1,2σ ROIs: statistics is too low to

conclude on their parent distribution

Events within ±1σ

Events within ±1–2σ

Black – 2νββ Blue – 238U X10Red – 40K X10 Green – 232Th X10

Cathode

Fiducial vol.

23

The EXO-200 Time Projection Chamber (TPC)

CathodeField shaping rings

Charge detection wiresSignal cables

APDs Teflon reflector

24

2011 EXO-200 2νββ Measurement

T1/2 = 2.11 · 1021 yr (± 0.04 stat) (± 0.21 syst) [arXiv:1108.4193]

Zoomed in

31 live-days of data 63 kg active mass Signal/background ratio 10:1 (as good as 40:1

for some extreme fiducial volume cuts

Single - cluster Multiple - cluster

2νββ

Wire Gains• gains of wire channels measured with charge calibraQons

• This is further corrected using the pair producQon peak (1593 keV) from 232Th 2615 keV gamma deposiQons.

• Have also individually measured the electronic transfer funcQon of each channel, which are used to reconstrucQon the charge signals

• With all this, and the excellent purity, the charge resoluQon improved from 4.5% to 3.4% at 2615 keV

25

Correcting for light response

Cathode Ring

APD Plane

APD Plane

Disabled APD gang

26

Use full absorption peak of 2615 keV gamma from 208Tl to map light response in TPC

Linearly interpolate between 1352 voxels

27

Simulated spectra generation

Dotted line is Geant4 simulated energy deposition from 228Th source.

Solid line is energy spectra resulting from the convolution of the MC energy deposition with the energy resolution model.

SS MS

Improvements in progress

• New Radon purge for the air gap between Pb and Cryostat

• Energy resolution improvements

• Further improvements of 3D reconstruction and multiplicity assignment

28

EXO Sensitivity to〈mββ〉

29

mmin [eV]

|m|

[eV

]

NS

ISC

osmological Lim

it

Current Bound

10 4 10 3 10 2 10 1 110 4

10 3

10 2

10 1

1

123

EXO-200 this result

KK Claim 2006

Adapted from Bilenki, Giunti arXiv:1203.5250v1

EXO multi-ton (projection)

session14 farine r1 -

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