EXO-Development Program

DUSEL WorkshopWashington, November 2007

David SinclairCarleton/TRIUMF

We need to develop new strategies to eliminate backgrounds to probe the allowed space

Barium tagging may offer a way forward

Inverted

Normal

Xe offers a qualitatively new tool against background:Xe offers a qualitatively new tool against background:136136Xe Xe 136136BaBa++++ e e-- e e- - final state can be identified final state can be identified using optical spectroscopy using optical spectroscopy (M.Moe PRC44 (1991) 931)(M.Moe PRC44 (1991) 931)

BaBa++ system best studied system best studied(Neuhauser, Hohenstatt,(Neuhauser, Hohenstatt,Toshek, Dehmelt 1980)Toshek, Dehmelt 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 additional constraintconstraint•Huge backgroundHuge background reductionreduction

22PP1/21/2

44DD3/23/2

22SS1/21/2

493nm493nm

650nm650nm

metastable 80smetastable 80s136Ba+

BaBa++ spectroscopy in high pressure noble gases spectroscopy in high pressure noble gases

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

The signal amplitudeThe signal amplitudeis proportionalis proportionalto integersto integers

Millikan experiment with ions in Millikan experiment with ions in vacuumvacuum

1) Resonance Ionization Spectroscopy

•After a real-time ββ trigger, a ~400 μm fiber with a metallized end and biased at a negative potential is inserted near the event site in LXe.

• The Ba+ ion is attracted to the tip and trapped

• The ion is released with a laser pulse, resonantly ionized with two other pulses, and injected into the trap where it is detected.

Ba tagging for the Liquid Detector

Currently, two ion transfer methods are under parallel development, both involving the capture and transport of the ion on the surface of a specially designed tip

Cryo-tip

sensor

Cu cold finger

Au-coated leads

Vespel sleeves

W heater wire

lHe cryostat

Ice sensor

LXe cell

Actuator

Shielded cables To LCR meter

2mmRead-out cables

Results – PID-controlled Thin Layer Freezing

in 700 mbar Xe from liquid Xe

PID control temp, feedback on capacitance

Liquid or Gas

Liquid

Compact detectorNo pressure vesselSmall shield -> lower purity reqd.

Gas

Energy resolutionTracking & multi-site rejectionIn-situ Ba tagging angular correlation

Large CryostatPoorer energy, tracking resolutionEx-situ Ba tagging

Large detector

Needs very large shield

Pressure vessel is massive

Pros

Cons

Understanding Physics of Double Beta Decay Recent paper by Ali, Borisov and Zhuridov Probing New Physics in the Neutrinoless

Double Beta Decay using Electron Aangular Correlation arXiv:0706.4165v2

Anode PadsMicro-megas

WLS BarElectrode

For 200 kg, 10 bar, box is 1.5 m on a side

Possible concept for a gas double beta counter

Xe Gas+ ???

. . . . . . . .

. . . . . . . .PMT

Laser

Grids

Technical issues for a Gas counter Need to demonstrate good energy resolution

(<1% to completely exclude ) Want to have gas gain if possible Need to demonstrate Ba tagging

Deal with pressure broadening Ba ion lifetime Ba++ -> Ba+ conversion Can we cope with background of scattered light

Progress on energy resolution

Xe Energy Spectrum 3cm 2b 5992

0

50

100

150

200

500 510 520 530 540 550 560 570 580 590 600

Energy (MeV)

Co

un

ts

Alpha spectrum at 2 b pressure.

= 0.6%

Energy Resolution in Gas

Better than 1% (sigma) achieved in pure Xe and several mixtures

In pure Xe, at 2 bar, amplitude is constant to 0.2% for drift up to 17 cm

Pure Xe is slow

Other gas requirements

If we add something to the gas to speed up electrons and quench gain stage then Does the additive kill the 172 nm light Do electrons attach to the additive Will the additive trap Ba ions Will the additive convert Ba++ to Ba+

Ba tagging in high-pressure Xe We need to deal with pressure broadening Requires higher laser power to get

fluorescence rate (perhaps factor of 1000) Higher density gives more scattering However, in high pressure Xe the D state will

quickly de-excite collisionally Plan to excite with blue laser and look for red

emission photons

Xe offers a qualitatively new tool against background:Xe offers a qualitatively new tool against background:136136Xe Xe 136136BaBa++++ e e-- e e- - final state can be identified final state can be identified using optical spectroscopy using optical spectroscopy (M.Moe PRC44 (1991) 931)(M.Moe PRC44 (1991) 931)

BaBa++ system best studied system best studied(Neuhauser, Hohenstatt,(Neuhauser, Hohenstatt,Toshek, Dehmelt 1980)Toshek, Dehmelt 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 additional constraintconstraint•Huge backgroundHuge background reductionreduction

22PP1/21/2

44DD3/23/2

22SS1/21/2

493nm493nm

650nm650nm

LaserIn

Red lightout

De-excite bycollisions

Future Program

Demonstrate the liquid detection technique at WIPP, measure ( in Xe, Measure (if at HM value

Develop the Ba tagging for a liquid detector Demonstrate a gas phase detection Develop the Ba in-situ tag in gas phase Build the ultimate, ton scale detector for

double beta decay