Upload
ashlee-jackson
View
214
Download
0
Tags:
Embed Size (px)
Citation preview
EXO-GAS Detector
Status report for the SNOLAB EAC August 2007
EXO Canada Team
• Laurentian– J. Farine, D. Hallman, C. Virtue, U. Wichoski– Adam Blais (Summer Student)
• Carleton– M. Dixit, K. Graham, C. Hargrove, D. Sinclair– C. Green, E. Rollin (Grad. Students)– K. McFarlane (Engineer) L. Anselmo
(Chemist)
Heidelberg-Moscow Results for Ge double beta decay
57 kg years of 76Ge data Apply single site criterion
Normal and Inverted Mass Hierarchies
We need to develop new strategies to eliminate backgrounds to probe the allowed space
Barium tagging may offer a way forward
Inverted
Normal
EXO – Enriched Xenon Observatory
• Look for neutrino-less double beta decay in Xe• 136Xe --- 136Ba + e- + e-
• Attempt to detect ionization and the Ba daughter• Ba is produced as ++ ion• Ba+ has 1 electron outside Xe closed shell so
has simple ‘hydrogenic’ states• Ba++ can (?) be converted to Ba+ with suitable
additive
Advantages of Xe
• Like most noble gases/liquids it can be made extremely pure
• No long lived radioactive isotopes
• High Q value gives favourable rates
• Readily made into a detector
• Possible barium tagging to eliminate backgrounds
Liquid or Gas
Liquid
Compact detectorNo pressure vesselSmall shield -> lower purity reqd.
Gas
Energy resolutionTracking & multi-site rejectionIn-situ Ba tagging
Large CryostatPoorer energy, tracking resolutionEx-situ Ba tagging
Large detector
Needs very large shield
Pressure vessel is massive
Liquid Detector EXO 200
• Objectives– Prove the liquid detection concept– Measure decay rate for Xe– Test the HM claim for observation of
• Under construction at Stanford for deployment at WIPP
• Major engineering support from Vance Strickland
Status of 2Status of 2νν mode in mode in 136136XeXe
22νββνββ decay has never been observed in decay has never been observed in 136136Xe. Xe. Some of the lower limits on its half life are close to (and inSome of the lower limits on its half life are close to (and in
one case below) the theoretical expectation.one case below) the theoretical expectation.
T1/2 (yr)
evts/year in the 200kg prototype
(no efficiency applied)
Experimental limit
Leuscher et al >3.6·1020 <1.3 M
Gavriljuk et al >8.1·1020 <0.6 M
Bernabei et al >1.0·1022 <48 k
Theoretical prediction
QRPA (Staudt et al) [T1/2
max] =2.1·1022 =23 k
QRPA (Vogel et al) =8.4·1020 =0.58 M
NSM (Caurier et al)(=2.1·1021
)(=0.23 M)The 200kg EXO prototypeThe 200kg EXO prototype
should definitely resolve this issueshould definitely resolve this issue
Assumptions: Assumptions: 1)1) 80% enrichment in 13680% enrichment in 1362)2) Intrinsic low background + Ba tagging eliminate all radioactive backgroundIntrinsic low background + Ba tagging eliminate all radioactive background3)3) Energy res only used to separate the 0Energy res only used to separate the 0νν from 2 from 2νν modes: modes: Select 0Select 0νν events in a ±2 events in a ±2σσ interval centered around the 2.481MeV endpoint interval centered around the 2.481MeV endpoint4)4) Use for 2Use for 2νββνββ T T1/21/2>1·10>1·102222yr (Bernabei et al. measurement)yr (Bernabei et al. measurement)
** (E)/E = 1.6% obtained in EXO R&D, Conti et al Phys Rev B (E)/E = 1.6% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 05420168 (2003) 054201†† (E)/E = 1.0% considered as an aggressive but realistic guess with large light(E)/E = 1.0% considered as an aggressive but realistic guess with large light collection areacollection area‡‡ QRPA: A.Staudt et al. Europhys. Lett.13 (1990) 31; Phys. Lett. B268 (1991) 312QRPA: A.Staudt et al. Europhys. Lett.13 (1990) 31; Phys. Lett. B268 (1991) 312## NSM: E.Caurier et al. Phys Rev Lett 77 (1996) 1954 NSM: E.Caurier et al. Phys Rev Lett 77 (1996) 1954
EXO neutrino effective mass sensitivityEXO neutrino effective mass sensitivity
Case Mass(ton)
Eff.(%)
Run Time(yr)
σE/E @ 2.5MeV
(%)
2νββBackgroun
d(events)
T1/20ν
(yr, 90%CL)
Majorana mass(meV)
QRPA‡ (NSM)#
Conservative 1 70 5 1.6* 0.5 (use 1) 2*1027 33 (95)Aggres
sive 10 70 10 1† 0.7 (use 1) 4.1*1028 7.3 (21)
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
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
Lasers
Grids
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 GasIsobutaneTEA
. . . . . . . .
. . . . . . . .PMT
Lasers
Grids
Triggers
• Level 1 – Light => event in fiducial volume– Light => energy = Q +- 10%
• Level 2– Ionization => energy = Q +- 3%– 2 Bragg peaks– Single site event
• Determine Ba location• Start search for Ba
Gas Option for EXO
• Need to demonstrate good energy resolution (<1% to completely exclude ) tracking,
• Need to demonstrate Ba tagging– Deal with pressure broadening– Ba ion lifetime– Ba++ -> Ba+ conversion– Can we cope with background of scattered
light
Tasks to design gas EXO
• 1) Gas Choice– Measure Energy resolution for chosen gas– (Should be as good as Ge but this has never
been achieved)– Measure gain for chosen gas– Measure electron attachment for chosen gas– Understand optical properties– Measure Ba++ -> Ba+ conversion– Measure Ba+ lifetime
Tasks to design EXO Gas
• 2) TPC Design– What pressure to use– What anode geometry to use– What chamber geometry to use– What gain mechanism to use– Develop MC for the detector– Design electronics/DAQ
Tasks to design EXO Gas
• 3) Ba Tagging– Demonstrate single ion counting– Understand pressure broadening/shift– Understand backgrounds– Fix concept
Tasks to design EXO Gas
• 4) Overall Detector concept– Fix shielding requirements and concepts– Design pressure containment– Fix overall layout
Gas Properties
• Possible gas – Xe + iso-butane + TEA• Iso-butane to keep electrons cold, stabilize
micromegas/GEM• TEA
– Converts Ba++ -> Ba+• Q for TEA + Ba++->TEA+ + Ba+* ~ 0
– Converts 172 nm -> 280 nm?– ? Does it trap electrons?– ?Does it trap Ba+?
Measuring Gas properties
• Gridded ion chamber being used to measure resolution, drift of electrons using alpha source
AnodeGrid
Field Rings
Source
Movable source holderContacts rings with wiper
Gridded Ion Chamber
Progress on energy resolution – Pure Xe, 2 Bar
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 Spectrum for Xe + CH4 (5%)
Corrected Energy Spectrum (10 cm)
0
50
100
150
200
450 460 470 480 490 500 510 520 530 540 550
Energy (arb. units)
Co
un
ts
Amplitude vs risetime
0
0.1
0.2
0.3
20 40 60 80 100 120 140
rise time (16 ns/bin)
Am
plit
ud
e (
Arb
. un
its
)
Amplitude and resolution vs source distance
0.40.450.5
0.550.6
0.650.7
0.750.8
0 5 10 15 20
Source distance (cm)
resolution
Peak Amplitude
Xe + 5% CH4
Xe + Isobutane Peak vs Drift Distance
547539
518
497490
500
510
520
530
540
550
0 5 10 15 20
Drift (cm)
Pea
k am
pli
tud
e
Note: (1) peak width was constant at ~0.6% over the range(2) Gas was not purified but was spec’d at 99.9%
Current status on energy resolution
• Ionization in gaseous Xe gives adequate energy resolution, even for alpha particles.
• We can now use this to explore gain options
Studying Ba ions in high pressure Xe gas
- - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - -
Thin (5 m) Pt wire + BaGrid 1
Grid 2
PMT
__ __ __ __ __ __ __ __ __ __ __ __ __ Laser Beams
Pulse red and blue lasers out of phase with each other
Filter
Ion production in test cell (detection using Channeltron)Ion detection from hot Pt wire
1
10
100
1000
10000
100000
1000000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Time since heating pulse (s)
Co
un
ts p
er
1 m
s b
in
Progress on Ba tagging
Problems with Proposed technique
• It appears that the D state de-excites through collisions on a timescale short compared to our laser pulsing
• This would allow a different approach
• Use cw blue laser and look for red fluorescence lines
• Red sensitive PMT on order
Si detector228Th
Lens
PMT
Laser Beam
Concept for single ion fluorescence of Ra
Plans (Dreams)
• We are working to address the technical issues associated with a large gas Xe double beta decay detector
• If all goes well we will seek funding to build a 200 kg gas detector with Ba tagging
Xe200 kg
at 18.2 psia
VacuumAround acrylic
blocks ?H2O
(3.3 psi + 18.2 psi)~ 21.4 psia
H2O(7.7 psi + 18.2)
~ 25.9 psia
Acrylic Blocks9 tonnes
(Fills 25% of space)
Crinkled Cubic Copper Liner3,000 lb (if 0.1 inch thick)
10.2 feet each side
Acrylic Cylindrical Shell14.9 feet diameter,
12.2 feet highWater Tank28 diameter
for 2 meters H2O
EXO GAS DETECTOR CONCEPT200 Kg
Elevation
Plan View
Note: Decreasing the Xe pressureto 1 bar requires increasing the coppertank to 11 foot sides.
Water Shield490 tonnes water
If filled without internals
Longer term plans
• If things go really well we can consider a ton scale detector.
• Could be either liquid or gas• If Ba tagging works very well then
incentive to use separated isotope Xe is weaker
• A detector of several tons could be accomodated in either the cube hall or the cryopit.
EXO Progress Update
Laurentian University
Jacques Farine
EXO Gas Option Simulation
First step: containment efficiencies
• Pressure and mass dependence
• Cylinder, take H=2R to minimize S/V
• Filled with 136Xe
• Cu walls
• 0 decay, Q = 2457.8 keV
• Differentiate e–//both crossing fid. vol.
Uncertainties obtained from 20 independent simulations. + Points include detailed low energy processes, scintillation and E=1kV/cm ( .. 30x CPU cycles).
2 / 0 differential c at edges
• Simulations for 1T at 5 atm, equator
• 10,000 evts ea.• Contam. of 2 in 0
increases towards the edge
• > Optimize fiduc. volume and/or vary fraction of contamination
Next steps
• Add chemical composition / drift / attenuation / absorption / attachment // light+charge readout
• Add backgrounds as source of singles• Write code to detect Bragg peaks • For single/double separation, determine:
– Contamination / sacrifice– Effect of Bremsstrahlung
• Light collection options > E resolution
Studies related to bothL+G Options
Material screening - radon emanation tests
• Continued program at SNOLAB• Sensitivity 10 220Rn/day, 20 222Rn/day• Measure EXO-200 plumbing• No substantial source• Clean !
Characterize counters for Ar/Xe
• Allow for:– Absolute emanation
measurements– Diffusion studies in
• Absolute cross-calibration between gasesN2 = Ar; Xe 23% lower
Radon Trap Development1) ESC on EXO-200• Augmented with:
– CO2 trap
– Rn source
– Water vapour trap
– Radon trap Mark I (LN2)
– Heat exchanger
– Recirculation pump
• Study Rn removal efficiency:– In misc. gases Air/N2/Ar > Xe
– Rn trap Mark I
Radon trap tests at ES-III (Stanford)
Mark I trap: 2” of SS wool at LN2, multiple passes efficiency too low (60% in 160 mbar N2) - sets scope
Radon Trap Development
2) At SNOLAB
• 222Rn and 210Rn sources development
• Radon extractor board as trap testbed
• Refrigerator purchased
• Cold head integration underway
• Xenon purchased
• Xe plumbing assembly initiated (w/ RCV vessels)
• ESC integration underway
Xenon heat exchanger
in construction
Diffusion of Rn in Xe
Reduction factor along dead legs• Known, irreducible source term• Want max. ingress rate at distance L• For 220/222Rn in N2/Ar/Xe
Theory - KTG in binary, dilute mixture, calculate D12
• 1D diffusion model with decay
Experimental check Diffusion length for 222Rn at 1 atm:
d = 2m in Ar; 1.2m in Xe
LGas at p,T