A Gas Option for EXOA Gas Option for EXO

David SinclairDavid SinclairEXO WeekEXO Week

January 2006January 2006Note – Most of the ideas here come from a discussion with Bill

Why Investigate a Gas OptionWhy Investigate a Gas OptionGas counter would allow tracking of Gas counter would allow tracking of

electronselectronsBetter rejection of gamma backgroundsBetter rejection of gamma backgrounds

Single site criteriaSingle site criteriaTwo Bragg peak criteriaTwo Bragg peak criteria

Possibly better energy resolution?Possibly better energy resolution?Better prospects for in situ Ba taggingBetter prospects for in situ Ba tagging

Gas Option Con’sGas Option Con’sMuch larger volumeMuch larger volumeShielding more difficultShielding more difficulthigh pressure containmenthigh pressure containment

ObjectivesObjectivesTo demonstrate a feasible concept for a To demonstrate a feasible concept for a

gas phase Xe detector for bb decaygas phase Xe detector for bb decay If successful, to build a 200 kg prototypeIf successful, to build a 200 kg prototype If really successful, expand to tonne scaleIf really successful, expand to tonne scale

->->->->->->->->->->->->->->->->->->->->

Anode PadsMicro-megas

WLS BarElectrode

Blue/red laser

WLS BarsWire cathode

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

Possible concept for a gas double beta counter

Challenges for a Gas EXOChallenges for a Gas EXODemonstrate good energy resolution in a Demonstrate good energy resolution in a

gasgasDecide on gas mixture – ‘to quench or not Decide on gas mixture – ‘to quench or not

to quench’to quench’ If quench, how to measure ZIf quench, how to measure ZDemonstrate gain and trackingDemonstrate gain and tracking

Ionization test chamberUnder construction atCarletonShould be completed andTaking date ~ 2 months

Work much furtherAdvanced at NeuchatelOn micromegas

Issues – Ba taggingIssues – Ba taggingNeed to demonstrate a robust Ba tagging Need to demonstrate a robust Ba tagging

schemeschemeDemonstrate Ba+ livetime in Xe gasDemonstrate Ba+ livetime in Xe gasDemonstrate Ba++ -> Ba+ conversionDemonstrate Ba++ -> Ba+ conversionMeasure Ba tagging efficiencyMeasure Ba tagging efficiencyDemonstrate low false tagging probabilityDemonstrate low false tagging probability

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 80s

Problems with in-situ taggingProblems with in-situ taggingPressure broadening implies lower Pressure broadening implies lower

signal/laser power ratio (?x1000)signal/laser power ratio (?x1000)Lack of exact location means broad laserLack of exact location means broad laserLack of exact location precludes focused Lack of exact location precludes focused

detectiondetectionTime available for measurement is smallTime available for measurement is smallAll lead to much greater background/signal All lead to much greater background/signal

compared with trapped sourcecompared with trapped source

Background Rejection OptionsBackground Rejection Options 1) Pulse Blue and Red lasers out of phase, look 1) Pulse Blue and Red lasers out of phase, look

for blue light only when blue laser is off (few for blue light only when blue laser is off (few microsecond periods)microsecond periods) AOM can give factor ~1000 contrast, using 2 should AOM can give factor ~1000 contrast, using 2 should

give 10give 105 5 Can also consider Pockels cells.Can also consider Pockels cells. Look in plane of polarization at 90 degrees only Look in plane of polarization at 90 degrees only

or use polaroidor use polaroid Use narrow band filter to limit angular Use narrow band filter to limit angular

acceptanceacceptance Use atomic filteringUse atomic filtering Take great care to minimize scattering – Use AR Take great care to minimize scattering – Use AR

coated laser windows and lots of bafflingcoated laser windows and lots of baffling

Ba tagging ProgrammeBa tagging ProgrammeFind effective source for Ba ions in XeFind effective source for Ba ions in XeFind fluorescence signal from Ba ionsFind fluorescence signal from Ba ionsMeasure pressure shift/broadening for Ba Measure pressure shift/broadening for Ba

ions in Xeions in XeMeasure Ba ion lifetime in XeMeasure Ba ion lifetime in XeStudy background rejection techniquesStudy background rejection techniquesPush towards single atom levelsPush towards single atom levels

Ba ion production in XenonBa ion production in XenonEvaporate Ba onto thin (125 ug/cm^2) Pt Evaporate Ba onto thin (125 ug/cm^2) Pt

(on Mylar)(on Mylar)Focus pulsed laser onto back of Pt (405 Focus pulsed laser onto back of Pt (405

nm, 50 mW, ~3 uS, few um) to heat to nm, 50 mW, ~3 uS, few um) to heat to ~300C~300C

Expect several hundred Ba atoms to be Expect several hundred Ba atoms to be released per pulse – ions?released per pulse – ions?

Exponential dependence on pulse widthExponential dependence on pulse width

405 nm laser2 uS

Laser window

Lens

Ba on Pt on Mylar

Grid

View Port

PMT

Laser Beam

Lasers for gas phaseLasers for gas phaseNeed highest available power in tuned Need highest available power in tuned

laserslasersWavelengths are most inconvenientWavelengths are most inconvenientFor blue use Krypton pump (Coherent For blue use Krypton pump (Coherent

Sabre 3W) and ring dye (899) with Sabre 3W) and ring dye (899) with Coumarin 102 dye Coumarin 102 dye

For red use Verdi (532 nm 8W) and ring For red use Verdi (532 nm 8W) and ring dye (DCM special)dye (DCM special)

Ba tagging test chamber

Ba is evaporated in the Green cross then movedTo the lower cube

405 nm light enters backOf cube to creat Ba ions

493/650 laser light entersWindows in extended arms

PMT faces view port

Grid in front of viewport Drifts Ba ions into the beam

Status of Ba studiesStatus of Ba studiesAll optics and lasers on order or deliveredAll optics and lasers on order or deliveredMain lasers due mid MarchMain lasers due mid MarchDesign essentially complete on chamberDesign essentially complete on chamberAlmost entirely off the shelf componentsAlmost entirely off the shelf componentsShould be assembled and looking for Ba Should be assembled and looking for Ba

by summerby summer

Long Term ProgrammeLong Term ProgrammeComplete initial studies of both resolution Complete initial studies of both resolution

and tagging ~ 1 yearand tagging ~ 1 yearDesign/construct mini gas EXODesign/construct mini gas EXO

~15 cm diameter~15 cm diameter Include trackingInclude tracking Include steerable laser Include steerable laser Use 134,137 Cs sourcesUse 134,137 Cs sourcesDemonstrate full functionality of a double beta Demonstrate full functionality of a double beta

detectordetector

Longer Term planLonger Term plan If everything works and if Gas option looks If everything works and if Gas option looks

interestinginterestingBuild 200 kg gas prototypeBuild 200 kg gas prototype