SNOLAB and EXO David Sinclair SNOLAB Workshop August 2005

EXO Search for double beta decay using Xe Search for double beta decay using Xe Identify decay energy by ion detection Identify decay energy by ion detection Control background by tagging events with Ba daughter Control background by tagging events with Ba daughter 200 kg separated isotope liquid Xe prototype under construction – will be installed at WIPP 200 kg separated isotope liquid Xe prototype under construction – will be installed at WIPP

Canadian participation in EXO Carleton/Laurentian groups Carleton/Laurentian groups 7 Canadian faculty 7 Canadian faculty First R&D funding in April First R&D funding in April Role clarified in July collaboration meeting Role clarified in July collaboration meeting

Xe offers a qualitatively new tool against background: 136 Xe 136 Ba ++ e - e - final state can be identified using optical spectroscopy (M.Moe PRC44 (1991) 931) Ba + system best studied (Neuhauser, Hohenstatt, Toshek, Dehmelt 1980) Very specific signature shelving Single ions can be detected from a photon rate of 10 7 /s Important additionalImportant additional constraint constraint Huge backgroundHuge background reduction reduction 2 P 1/2 4 D 3/2 2 S 1/2 493nm 650nm metastable 80s

Possible Gas Version Gas counter would allow tracking Gas counter would allow tracking Better rejection of gamma backgrounds Better rejection of gamma backgrounds Single site criteria Single site criteria Two Bragg peak criteria Two Bragg peak criteria Possibly better energy resolution Possibly better energy resolution Better prospects for in situ Ba tagging Better prospects for in situ Ba tagging

Liquid Advantages Smaller active volume Smaller active volume Easier shielding Easier shielding No high pressure containment No high pressure containment Canadian groups will develop Gas Option Canadian groups will develop Gas Option

Objectives To demonstrate a feasible concept for a gas phase Xe detector for bb decay To demonstrate a feasible concept for a gas phase Xe detector for bb decay If successful, to build a 200 kg prototype If successful, to build a 200 kg prototype If really successful, expand to tonne scale If really successful, expand to tonne scale

->->->->->->->->->->->->->->->->->->->-> Anode Pads Micro-megas WLS Bar Electrode Blue/red laser WLS Bars Wire cathode For 200 kg, 10 bar, box is 1.5 m on a side Possible concept for a gas double beta counter

Issues – Energy Resolution Need to demonstrate ~1% or better Need to demonstrate ~1% or better What gain mechanism to use? What gain mechanism to use? Micromegas? Micromegas? What gas additives to use? What gas additives to use? Quench gas? Quench gas? Drift velocity? Drift velocity? WLS for 178 nm light? WLS for 178 nm light? Loss of 178 nm light? Loss of 178 nm light? TMAE or other to convert light to electrons? TMAE or other to convert light to electrons? What is the optimal pressure? What is the optimal pressure?

Issues - Tracking Want to identify decay vertex Want to identify decay vertex Want to see 2 Bragg peaks Want to see 2 Bragg peaks Want to reject multi-site events Want to reject multi-site events Eventually want to look and angular correlation Eventually want to look and angular correlation

Issues – Ba tagging Need to demonstrate a robust Ba tagging scheme Need to demonstrate a robust Ba tagging scheme Demonstrate Ba+ livetime Demonstrate Ba+ livetime Demonstrate Ba++ -> Ba+ conversion Demonstrate Ba++ -> Ba+ conversion Measure Ba tagging efficiency Measure Ba tagging efficiency Demonstrate low false tagging probability Demonstrate low false tagging probability

Engineering Much larger volume suggests water shielding to get purity Much larger volume suggests water shielding to get purity Look at thin gas containment, high pressure water, use cavern to contain pressure Look at thin gas containment, high pressure water, use cavern to contain pressure

Programme – Energy Resolution Explore TPC energy resolution in Xe w/wo optical detection – Carleton/Laurentian/Neuchatel+Saclay? Explore TPC energy resolution in Xe w/wo optical detection – Carleton/Laurentian/Neuchatel+Saclay? Optimize micromegas Optimize micromegas Explore gas mixtures Explore gas mixtures Explore scintillation detection Explore scintillation detection

Programme - Tracking Carleton Carleton Initially need MC study Initially need MC study Look at impact of magnetic fields Look at impact of magnetic fields

Programme – Ba Tagging Carleton/Laurentian/Colorado Carleton/Laurentian/Colorado Ba line widths Ba line widths Ba lifetime Ba lifetime Tagging schemes Tagging schemes Demonstrate reliable, in-situ tagging Demonstrate reliable, in-situ tagging Study backgrounds Study backgrounds Note – Line widths -> high laser power, need selective detection Note – Line widths -> high laser power, need selective detection Toy Model – Pulse blue laser, look for blue light when laser off, use fluorecene (peak absorption 490 nm, emission 520 nm, 97% Quantum yield, 80,000 /mol/cm absorption) + bialkali PMT Toy Model – Pulse blue laser, look for blue light when laser off, use fluorecene (peak absorption 490 nm, emission 520 nm, 97% Quantum yield, 80,000 /mol/cm absorption) + bialkali PMT

Programme Do studies of energy resolution in small test cell at Carleton (~1 year) Do studies of energy resolution in small test cell at Carleton (~1 year) Do MC studies and optimize tracking (~1 year) Do MC studies and optimize tracking (~1 year) Develop laser lab for Barium counting at SNOLAB Develop laser lab for Barium counting at SNOLAB Build ~30 cm test chamber to operate underground at SNOLAB to demonstrate full concepts including trigger, tracking, tagging (use 134Cs to simulate decay) Build ~30 cm test chamber to operate underground at SNOLAB to demonstrate full concepts including trigger, tracking, tagging (use 134Cs to simulate decay) Develop 200 kg prototype to be ready in ~3 years when liquid prototype tests complete at WIPP Develop 200 kg prototype to be ready in ~3 years when liquid prototype tests complete at WIPP

Schedule Aim to have a concept in 1 year Aim to have a concept in 1 year 1% energy resolution 1% energy resolution Demonstrated tagging Demonstrated tagging Conceptual design for vessels, shielding Conceptual design for vessels, shielding Demonstrate concepts with 30 cm chamber in 2 years Demonstrate concepts with 30 cm chamber in 2 years Start construction of 200 kg detector in cavern capable of expansion to tonne scale in 3 years Start construction of 200 kg detector in cavern capable of expansion to tonne scale in 3 years