tonne scale next at snolab

TONNE SCALE NEXT AT SNOLAB

F. Monrabal University of Texas at Arlington

for the NEXT Collaboration

Future Projects Workshop1

MAJORANA LANDSCAPE

➤ Latest results barely touching Inverse Hierarchy region.

➤ Need to reach ~1027 years lifetimes.

➤ Ton scale experiments are needed to reach these lifetimes.

➤ Background rate objective <1 evt/tonne/year.

2

EXPLORING THE IH

100 % efficient Xe experiment(using a “reasonable NME set”): 2 ton year to explore IH with 1 background event per ton per year

30 % efficient Xe experiment: •10 ton year to explore IH with 1

background event per ton per year •4.5 ton year to explore IH with 0.1

background event per ton per year

10

100

10 cts/tonne/year

1.0 cts/tonne/year

0.1 cts/tonne/year

10 cts/tonne/year at 30% Efficiency

1.0 cts/tonne/year at 30% Efficiency

0.1 cts/tonne/year at 30% Efficiency

102 103 104

Exposure (kg yr)

m (m

eV)

136Xe

3

HPXE-EL TECHNOLOGY

First target: To demonstrate “background free” (<1 evt/year) @ 100 kg scale

Ultimate target: To upgrade the technology “background free” (<1 evt/year) @ 1 tonne scale

X (mm)-60 -40 -20 0 20 40 60

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SIGNAL BACKGROUND

Figure 1: Monte Carlo simulation of signal (0nbb decay of 136Xe) and background(single electron of energy equal to the Q value of 136Xe) events in gaseous xenon at15 bar. The ionization tracks left by signal events feature large energy deposits (orblobs) in both ends.

Background tracks, however, are generated by single electrons, thus havingonly one end-of-track blob.

Natural radioactivity in detector materials and surroundings is, as inmost other 0nbb-decay experiments, the main source of background inNEXT. In particular, the hypothetical 0nbb peak of 136Xe (Qbb = 2458 keV)lies in between the photopeaks of two high-energy gammas emitted afterthe b decays of 214Bi and 208Tl, intermediate products of the uranium andthorium series, respectively. The daughter isotope of 214Bi, 214Po, emits anumber of de-excitation gammas with energies around and above the Qvalue of 136Xe [2]. Most of these gamma lines have very low intensity, andhence their contribution to the background rate is negligible. The gammaof 2447 keV (1.57% intensity), however, is very close to Qbb, and thus itsphotoelectric peak overlaps the signal peak even for energy resolutions asgood as 0.5% FWHM. The decay product of 208Tl, 208Pb, emits a de-excitationphoton of 2615 keV with an intensity of 99.75% [2]. Electron tracks fromits photopeak can lose energy via bremsstrahlung and fall in the region ofinterest (ROI) around Qbb defined by the energy resolution of the detector.Additionally, even though the Compton edge of the 2.6-MeV gamma is at2382 keV, well below Qbb, the Compton scattered photon can generate otherelectron tracks close enough to the initial Compton electron so that they arereconstructed as a single track with energy around Qbb.

The NEXT Collaboration is carrying out a thorough campaign of materialscreening and selection using gamma-ray spectroscopy (with the assistance

2

Energy resolution

(Intrinsic Energy resolution 0.3%FWHM) Topological signature

4

NOISELESS GAIN WITH ELECTROLUMINESCENCE!

Emission of scintillation light after atom excitation by a charge accelerated by a moderately large (no charge gain) electric field.

Linear process, fluctuations suppressed (effective Fano factor ~0.01)

Large gain (1500 ph./e-)

Used in NEXT to amplify the ionization signal. 5

TRACKING IN HPXE

X (mm)0 50 100 150 200

Y (

mm

)

-300

-250

-200

-150

Electrons travel on average ~10 cm (15 bar) each.

Trajectories highly affected by multiple scattering.

Electrons travel with almost minimum dE/dx except at the end-points where they generate “blobs”.

0νßß MC event

6

DETECTION CONCEPT

Phot

odet

ecto

rs�

It is a High Pressure Xenon (HPXe) TPC operating in EL mode.

It is filled with Xe enriched at 90% in Xe-136 (in stock) at a pressure of 15 bar.7

DETECTION CONCEPT

Phot

odet

ecto

rs�

Primary Scintillation light is detected by a plane of photosensors. It gives t0 of the event and the z position.

Primary Scintillation (S1)

8

DETECTION CONCEPT

Phot

odet

ecto

rs�

Tracking with SiPM

s

The event energy is integrated by a plane of radiopure PMTs located behind a transparent cathode (energy plane), which also provide t0.

The event topology is reconstructed by a plane of radiopure silicon pixels (SiPMs) (tracking plane).

Electroluminescence (S2)

9

WAVEFORMS IN NEXT

drift time

primary scintillationsignal: starting time of event

EL signal

S1 S2

10

ENERGY RESOLUTION

Na22Entries 341932Mean 304.2RMS 181.8

Energy (keV)0 100 200 300 400 500 600

Entri

es/b

in

0

500

1000

1500

2000

2500

3000

3500

4000 Na22Entries 341932Mean 304.2RMS 181.8

Calibrated S2 Charge (keV)600 610 620 630 640 650 660 670 680 690 700

Co

un

ts p

er

keV

0

10

20

30

40

50

1.0% FWHM

Direct 1/Sqrt(E) Energy resolution extrapolation from NEXT prototypes: 0.5-0.7% FWHM at Qββ

1.6% FWHM

5.7% FWHM

JINST 9 (2014) no.10, P10007 Nucl. Instrum. Meth. A708 (2013) 101-114

DBDM with 137Cs (662 keV) DEMO with

22Na (511 keV)

11

•Electron energy loss in gas is constant until the end of the trajectory (Bragg peak).

•Signal: spaghetti with two “meat balls”.

•Background: spaghetti with one “meat ball”.

•Electrons leave extended tracks in gas, which can be used 1) to veto beta electrons coming from outside, 2) to identify events with more than one track (typically background).

TOPOLOGY

high energy gamma

electron

12

THE POWER OF TOPOLOGY (MC)

Higher energy blob cand. energy (MeV)0 0.2 0.4 0.6 0.8 1 1.2

Low

er e

nerg

y bl

ob c

and.

ene

rgy

(MeV

)

0

0.2

0.4

0.6

0.8

1

1.2 Proportion of events

0

0.001

0.002

0.003

0.004

0.005

Energy blob 1(Higher energy)

Energy blob 2

(Lower energy)

Two electrons events: Both electrons have similar energies at the end-point

Double electrons signals

(208Tl double escape peak)

13


Low

er e

nerg

y bl

ob c

and.

ene

rgy

(MeV

)

0

0.2

0.4

0.6

0.8

1


0

0.001

0.002

0.003

0.004

0.005

THE POWER OF TOPOLOGY (MC)

End-point Energy 1 (Higher energy)

End-point Energy 2

(Lower energy)

One electron events: Very different energies at end-points.

Single electrons signals

(22Na 1.2 MeV gamma)

14

TOPOLOGY: DEMO DATA

Background rejection0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Sign

al e

ffici

ency

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Data

MC

Higher energy blob cand. energy (keV)0 200 400 600 800 1000 1200Lo

wer

ene

rgy

blob

can

d. e

negy

(keV

)0

200

400

600

800

1000

1200

Proportion of events

0

0.005

0.01

0.015

0.02

0.025

Higher energy blob cand. energy (keV)0 200 400 600 800 1000 1200

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er e

nerg

y bl

ob c

and.

ene

rgy

(keV

)

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0

0.005

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Tracking capabilities of NEXT DEMO • Double escape peak of Tl-208 and high energy gamma

photopeak of Na-22 used to mimic signal and background.

• Discrimination power of topological cut demonstrated in data: 68% signal efficiency for 24% background acceptance.

• Limitations due to small chamber compared with track length.

• Better performance expected in larger detectors. • Validation of Monte Carlo.

JHEP 1601 (2016) 104

208Tl 22Na

15

DECONSTRUCTING NEXT-WHITE

Mother can:12 cm copper plate that separates pressure from

vacuum and ads shielding.

Pressure vessel:316-Ti steel, 30 bar max pressure

Inner shield:copper, 6 cm thick

Time Projection Chamber:10 kg active region(@10bar), 50 cm drift length

Energy plane:12 PMTs,

operating at vacuum. 30% coverage

Tracking plane:1792 SiPMs, 1 cm pitch

16

THE CANFRANC UNDERGROUND LABORATORY

2500 wme

17

PRESSURE VESSEL

Stainless Steel 316 alloy. Radiopure and light

18

GAS SYSTEM

19

GAS SYSTEM

Triple diaphragm compressor to prevent leaks

cryo-recovery bottle getters

20

HAMATSU R11410 low radioactivity PMT

ENERGY PLANE

Copper plate to shield and protect PMTs

21

SensL series-C low radioactivity

TRACKING PLANE

Gain ~106

1cm pitch between sensors

kapton boards for radiopurity and allowing connexions behind the shielding

Teflon panels for extra reflection

22

FIELD CAGE AND HIGH VOLTAGE FEEDTHROUGH

Design and electric field simulation of the field cage and HVFT

130

10

2 ±0

,10

8,5

0(x16

) A

A

18

H8 + 0,

030

40

19

28

26°

±0,

10°

19,

36° ±

0,10

°

R3

R10

72

,10

H9 + 0,

070

80

R1

155,76 96,30

12

B

CORTE A-A

1-14UNF

N7

N8

0.05 A

0.05

A0.05

A

A

a4

70°

2,50

R0,50 R0,

25

R0,50

R0,25

3,4

5

DETALLE B ESCALA 5 : 1

N6

D

E

F

C

1 2 3 4

B

A

321 5

C

D

4 6 7 8

A

B

1 Se ha añadido rosca UNF

ApprovedDateDescriptionRevision

31/03/2015

A3 SHEET 1 OF 1

1:1

TITTLE

MATERIAL

DATE

DRAWN

PROYECT

CHECKED APPROVED

WEIGHT

SCALE

FORMAT SHEETDWG NO.

NORM PROCESSING/FINISH

EDITION

NEW

INSTITUTO DE FÍSICA CORPUSCULAR

I.F.I.C

Alberto Sara Sara

DRWP0006

DN65 flange HVFT V3

AISI 316Ti

HVFT operating at 28 kV at 7bar in pure Xenon

Field cage produces uniform electric field over the active volume.

23

Cathode, Gate, tpb coating for the anode and light reflector tube

CathodeGate

Anode plate

Light tube

FIELD CAGE

24

INSIDE NEXT-WHITE

25

FIRST WAVEFORMS

S1 Signal S2 Signal

Kr83m event in Xe@7bar

26

FIRST RESULTS‣ Source of Rb-83 inserted in the gas system inside a capsule. ‣ It decays with a half-life of 86 days to an excited state of Kr-83,

which diffuses in the whole system and eventually reaches the chamber.

‣ Kr-83 goes to ground state emitting electrons with total energy of ~41.5 keV.

‣ Almost point-like depositions, very useful to characterize the detector: electron attachment and drift velocity, geometric corrections.

PREL

IMIN

ARY

27

83Kr

Energy resolution at low energies matches previous results in prototypes

Still some radial dependance:

Room for improvement!

PREL

IMIN

ARY

28

Higher energy events need more detailed XYZ corrections due to finite extension of the event in the detector

Calibration on-going at higher energies.

1.9% FWHM@511keV. —>Goal: 1.5% FWHM

Very

PREL

IMIN

ARYNa22

Two X-rays clearly visible!

29

TRACKING RECONSTRUCTION

228Th source emits 2.6 MeV gamma from 208Tl.

This gamma has a double escape peak from pair production that produces signal-like events with two electrons.

Topology algorithms to be tested with this data.

Background rejection of the topology can be measured using this source.

Large rejection factors may be possible.

Single electron track

Pair production track

30

Detector completed.

Calibration data with radioactive sources on-going.

Physics run (background model, bb2nu): Q4 2017.

NEXT-WHITE SCHEDULE

31

anodecathodepressure!

vessel

light tubefield cage

energy !plane

tracking! plane

EL region

NEXT STEPS:

NEXT-ton

1 kg10 kg

100 kg

32

Pressure vessel:stainless steel,15 bar max pressure

Inner shield:copper, 12 cm thick

Time Projection Chamber:100 kg active region, 130 cm drift length

Outer shield:lead, 20 cm thick

Energy plane:60 PMTs,

30% coverageTracking plane:7,000 SiPMs,

1 cm pitch

NEXT 100 kg detector at LSC: main features

33

28

REJECTION OF BACKGROUND

•All detector materials are being screened to measure their radioactive budget or set limits.

•High pure Ge detectors, GDMS techniques.

Main backgrounds: Tl-208 - Compton tail of 2.6 MeV gamma. Bi-214 - Photopeak of 2.447 gamma, very close to Qbb!!!.

Energy (MeV)2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5 2.55 2.6

Even

ts /

5 Ke

V

1−10

1

10

100 meV, exposure = 500 kg year

bb0nu

Tl208

Bi214

Total background

Main backgrounds: 208Tl: 2.6 MeV gamma. 214Bi: 2.447 gamma.

All materials used for NEXT-100 construction have been screened:

Ge detectors, GDMS techniques,…

Simulated spectra near the Qßß for Xe

BACKGROUNDS IN NEXT-100

34

BACKGROUNDS IN NEXT-100: CUTS

fiducial cut

28





Energy (MeV)2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5 2.55 2.6

Even

ts /

5 Ke

V

1−10

1

10


bb0nu

Tl208

Bi214

Total background

Wide energy cut between 2.4 and 2.5 MeV

Single energy deposition

Two vs one blob


Low

er e

nerg

y bl

ob c

and.

ene

rgy

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28





Energy (MeV)2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5 2.55 2.6

Even

ts /

5 Ke

V

1−10

1

10


bb0nu

Tl208

Bi214

Total background

Region of interest

35

BACKGROUNDS IN NEXT-100: CUTS

•Signal simulated in the active volume.

•Tl and Bi simulated in the different components of the detector.

•Most of the background gammas either do not interact with the detector or deposit energy far from ROI.

36

BACKGROUND REJECTION IN NEXT-100

31


NEXT-100 background rate x 10-5 counts/(keV kg year).* come from actual measurements (otherwise are limit).

SiPM SUPPORT

DB PLUGs

DICE BOARDs

PMT SUPPORT

SAPPHIRE WINDOWs

PMTs

FIELD CAGE

QUARTZ PLATE

INNER COPPER SHIELDING

VESSEL

SHIELDING LEAD

0 2 4 6 8

Tl 208Bi 214

*

****

**

*

* ** *

Total expected background rate

< 4 x 10-4 cts / (keV kg year)

• Main measured contribution: PMTs (21 and 11 mBq in total) and kapton boards (glue between layers).

• Limits on copper and hdpe.

• Essential step towards the tonne scale.

JHEP 1605 (2016) 159

•All known background sources are included except 137Xe (TBD).

•Total expected background rate : <4·10-4 evt/keV kg year

•Expect a half life sensitivity of 6·1025

with an exposure of 275 kg·year.

•mßß ~[90-180] meV.

NME

37

NEXT-100 GOALS

➤ Extend NEXT technology towards near tonne scale.

➤ Measurement of background index at the 100 kg scale.

➤ Physics run:

➤ Precise measurement of 2 neutrino mode.

➤ Competitive sensitivity to neutrino-less process.

38

anodecathodepressure!

vessel

light tubefield cage

energy !plane

tracking! plane

EL region

NEXT STEPS:

1 kg10 kg

100 kg

15

THE NEXT DETECTORSPrototypes (2009-2014)

NEXT-DBDM

NEXT-DEMO

• ~1 kg of mass• Demonstration

of technology

First stage - NEW (2015-2019)

• ~10 kg of mass• Underground

operation• Background and ββ2ν measurements

NEXT-100 (2019-)

• 100 kg of mass• ββ0ν search

NEXT-ton (NAUSICAA)

NEW

• 1000 kg of mass

• ββ0ν search NEXT-ton

39

➤ Goal: Reach “background free” ~ton scale active volume.

➤ Approach: Multi-site multi-modular detectors.

•Simplify construction.

•Minimize single-point failure risk.

•Reduce uncertainty in case of a discovery.

•Possible operation of enriched and depleted Xenon in different modules.

➤ Possible locations: Europe (LSC, Gran Sasso), North America (SNOlab, SURF) and Australia (Stawell) or South America (Andes).

NEXT-TON:

40

NEXT-TON: WHAT DOES THE DETECTOR LOOK LIKE?

Symmetric TPC with two EL regions:

1.5 meter diameter

2 times 1.5 meter drift length

~500 kg of enriched Xenon

All SiPM read-out:

Improved radio purity

Better topological signature

Example of 3x3 mm2 SiPMs at 5mm pitch 41

•2-4modules will fit in moderate laboratory space.

•1-2 tonnes of Xenon active volume per site.

~3 m

~3 m


42

•Detectors plus shielding will easily fit in the “Cube Hall” or “Cryopit” at SNO.

•Details of external/shielding veto will be adapted to the specific lab characteristics.


43

NEXT PLANS

➤ Final design and construction of NEXT-100 in the next 18 months.

➤ DOE R&D funds for one year:

➤ Develop EL region and HVFT to allow good performance in large detectors.

➤ Broad R&D for improved performance and technological advances.

➤ Replace PMTs by SiPMs

➤ Improve topological background rejection: Improved tracking resolution.

➤ Barium tagging by Single Molecule Fluorescence Imaging.

➤ …

44

IFIC (Valencia), Santiago de Compostela, Girona, Politécnica Valencia, Autónoma Madrid

Coimbra GIAN, Coimbra LIP, Aveiro

ANL, FNAL, Iowa State, Ohio State, Texas A&M, Texas Arlington, Harvard

JINR (Dubna)

A.Nariño (Bogotá)

THANKS FOR YOUR ATTENTION!

Ben-Gurion University

45

BACK-UP

46

HOW TO IMPROVE TOPOLOGICAL SIGNATURE?

X (mm)-60 -40 -20 0 20 40 60

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m)

-60

-40

-20

0

20

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Y (m

m)

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-80

-60

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0

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✔

✔✔

✘

SIGNAL BACKGROUND

Figure 1: Monte Carlo simulation of signal (0nbb decay of 136Xe) and background(single electron of energy equal to the Q value of 136Xe) events in gaseous xenon at15 bar. The ionization tracks left by signal events feature large energy deposits (orblobs) in both ends.

Background tracks, however, are generated by single electrons, thus havingonly one end-of-track blob.

Natural radioactivity in detector materials and surroundings is, as inmost other 0nbb-decay experiments, the main source of background inNEXT. In particular, the hypothetical 0nbb peak of 136Xe (Qbb = 2458 keV)lies in between the photopeaks of two high-energy gammas emitted afterthe b decays of 214Bi and 208Tl, intermediate products of the uranium andthorium series, respectively. The daughter isotope of 214Bi, 214Po, emits anumber of de-excitation gammas with energies around and above the Qvalue of 136Xe [2]. Most of these gamma lines have very low intensity, andhence their contribution to the background rate is negligible. The gammaof 2447 keV (1.57% intensity), however, is very close to Qbb, and thus itsphotoelectric peak overlaps the signal peak even for energy resolutions asgood as 0.5% FWHM. The decay product of 208Tl, 208Pb, emits a de-excitationphoton of 2615 keV with an intensity of 99.75% [2]. Electron tracks fromits photopeak can lose energy via bremsstrahlung and fall in the region ofinterest (ROI) around Qbb defined by the energy resolution of the detector.Additionally, even though the Compton edge of the 2.6-MeV gamma is at2382 keV, well below Qbb, the Compton scattered photon can generate otherelectron tracks close enough to the initial Compton electron so that they arereconstructed as a single track with energy around Qbb.

The NEXT Collaboration is carrying out a thorough campaign of materialscreening and selection using gamma-ray spectroscopy (with the assistance

2

4.2 The standard NEXT topological analysis

After pre-selection the events were classified as signal or background based on the presenceof one or two “blobs” of energy in the reconstructed track, using the BFS algorithm andchoosing the longest of these paths to be the ordered path. Note that such a path may nothave included, in fact most likely did not include, all voxels in the event. The first and lastvoxels in the path were considered to be the beginning and end of the track. The energyin all voxels that were located within a given radius r

b

of the beginning of the track wassummed to give an energy E

b,1, and similarly at the end of the track to give an energy E

b,2.The results depend on the size of the voxel, which in turn is chosen to reflect the ex-

pected performance of the detector under specific operating conditions, as discussed above.Operation with pure xenon corresponds to 10 ⇥ 10 ⇥ 5 mm3 voxels (conservative), oper-ation with low diffusion mixtures correspond to voxel sizes of 2 ⇥ 2 ⇥ 2 mm3 (best ex-pected case) and voxels of 5⇥ 5⇥ 3 mm3 represent an intermediate case (best case in purexenon or conservative in low diffusion mixtures). Examples of events voxelized with sizesof 10⇥ 10⇥ 5 mm3 and 2⇥ 2⇥ 2 mm3 are shown in Figs. 4 and 5.

Figure 4. Projections in xy, yz, and xz for an example background (above) and signal (below)event voxelized with 10 x 10 x 5 mm3 voxels.

The histogram of E

b,1 vs. E

b,2 is shown in figure 6 for both signal and backgroundevents analyzed with both chosen voxel sizes. In this case, the distance between a voxeland the extremes of the track was calculated as “along-the-track distance,” in which thedistance between any two voxels was integrated along the reconstructed track (as opposedto computing the Euclidean distance).

Finally we apply a cut designed to choose signal events with two blobs and eliminatebackground events with only one blob, mandating that E

b,1 and E

b,2 are both greater than a

– 9 –

Figure 5. Projections in xy, yz, and xz for an example background (above) and signal (below)event voxelized with 2 x 2 x 2 mm3 voxels.

Figure 6. Computed blob energies E

b,1 vs. E

b,2 for signal (left) and 208Tl background (right)events with 10 x 10 x 5 mm3 voxelization (above) and 2 x 2 x 2 mm3 voxelization (below). Theblob radius chosen was r

b

= 18 mm for the 10 x 10 x 5 mm3 voxelization and r

b

= 15 mm for the2 x 2 x 2 mm3 voxelization.

– 10 –

10mm voxels

X pos (mm)200− 150− 100− 50− 0 50 100 150 200

Y po

s (m

m)

200−

150−

100−

50−

0

50

100

150

200

Voxe

l Cha

rge

(pes

)

0

2000

4000

6000

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X pos (mm)200− 150− 100− 50− 0 50 100 150 200

Y po

s (m

m)

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50−

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50

100

150

200

Voxe

l cha

rge

(a.u

.)

50

100

150

200

250

300

350310×

Effect of diffusion

47

SOME GAS MIXTURES REDUCE DIFFUSION

CO2: 0.1% (CH4: 1%) ->LD<2 mm

CO2: 0.05% (CH4: 0.5%) ->LD<2.5 mm

Molecular mixtures will reduce scintillation and EL light

Helium at larger concentrations (>10%) LD ~ 3 mm.

Helium won’t affect light production.

48

HOW TO IMPROVE RESOLUTION

Resolution is dominated by longitudinal and transverse diffusion.

It can be improved with gaseous mixtures

CO2 and CH4 are good candidates.

He is very promising as it will simplify gas system operations and won’t reduce EL production.

Read-out plane will need to be improved.

49

BA-TAGGINGBarium Tagging Concept

•Tag (using lasers) the presence of a Ba++ ion (in fact one needs to tag Ba+ since Ba++ first excited state lies in the extreme UV (75 nm) no accesible to conventional lasers

Ba++ Ba+

• Xe-136 decays produce Ba++

• Ba++ will drift towards cathode (hopefully without recombining)

• Coat cathode with PSMA molecule, which will capture BA++ (Dave Nygren’s proposal)

• PSMA + BA++ will fluoresce when illuminated with 342 nm light (broad band, 360-430… can design a system to detect blue light. Interrogation rate at ~100 kHz.

• This idea is a new form of Ba-tagging in gas which does not involve extracting the Ba++ ion to vacuum.

• Potentially: background free experiment.

Direct'Excita+on' Fiber'Coupled'

Data from barium tagging lab at

UTA

Notfluorescent Fluorescent

50

tonne scale next at snolab

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