Full EXO in Cryopit
Cryopit Workshop August 2011
David Sinclair
What is EXO
Enriched Xenon Observatory
Search for neutrinoless double beta decay in 136Xe
200 kg detector operating at WIPP
Gas R&D underway
Full EXO
A detector at up to 10 tonnes of sensitive material
Needed as next step towards the normal hierarchy
EXO neutrino effective mass sensitivity
Assumptions:
1) 80% enrichment in 136
2) Intrinsic low background + Ba tagging eliminate all radioactive background
3) Energy res only used to separate the 0ν from 2ν modes:
Select 0ν events in a ±2σ interval centered around the 2.481MeV endpoint
4) Use for 2νββ T1/2>1·1022yr (Bernabei et al. measurement)
Case
Mass
(ton)
Eff.
(%)
Run
Time
(yr)
σE/E @
2νββ
2.5MeV Background
(%)
(events)
Conserva
tive
1
70
5
1.6*
Aggressi
ve
10
70
10
1†
0.5 (use 1)
T1/20ν
(yr,
90%CL)
2*1027
0.7 (use 1) 4.1*1028
Majorana mass
(meV)
QRPA‡ (NSM)#
33
(95)
7.3
(21)
s(E)/E = 1.6% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 054201
† s(E)/E = 1.0% considered as an aggressive but realistic guess with large light
collection area
‡ QRPA: 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
*
EXO SAGENAP GG
4
Apr 16, 2004
EXO-200
Why limit to 10 T
Annual production of Xe ~ 40 T/a
~10% is 136Xe
Enrichment capacity ~ 1.8 T/a
Current world inventory is about 0.7 T
Probably cannot make too big a step in detector size
Why Xenon
Purity
Can be made into detectors
Excellent multi-site ID
Good background rejection
Least expensive isotope to produce
Possible Ba tag
Infrastructure Needs
Depth
We are attempting to measure one of the rarest
decay modes ever. Background control is critical.
Strongest case at DUSEL for deep site was for double
beta decay.
Pushing mass sensitivity -> pushing down
backgrounds
Even with barium tag, cosmogenics can hurt
We need to be deep
Infrastructure Needs
Cleanliness
Local radioactive backgrounds are critical
Just as in SNO we face a serious 208Tl background
The signal is in the ‘background wall’
Cleanliness is critical
Space
The space required for either a liquid or gas detector
at the tonne scale is the space available in the Cryopit
The Cryopit was designed with experients such as
these in mind
Services
No unusual requirements foreseen beyond what is
already provided
Safety
Both liquid and gas detectors have significant inert
material loads
A cryogenic liquid can vaporize rapidly giving
hazardous conditions
A gas detector is at high pressure and can give
hazardous conditions with failure
The Cryopit was designed to mitigate these risks
EXO Full LXe
Installed into SNOLAB CRYOPIT
Control Center
Offices, Kitchen
Restrooms
HFE Storage, UPS
Electrical Utilities
Machine Shop
Clean High Bay
Assembly area
Clean Access
Tunnel
Clean
Ba++ Tagging
& Electronics
Room
Water Purification
Cryogenics
Xe Storage
Showers/Gowning area
Clean room – Class 1K
Xe System & bottles
Clean room – Class 100/1K
3.1M Clear for
Equipment Access
EXO Full Building Size
7.1M X 6.1M X 14M
7.1M X 3.1M X 14M
Total Length 28M
EXO Full LXe Chamber Size
11.25M X 8.5M X 35.5M
1M Clear for
Personal Access
Clean Access
Tunnel
Staging / storage
area
Shielding Water
Gas Detector in Cryopit
Can operate at any pressure up to max pressure so
can start with partial fill
Upward load of ~300 T transfer to back
Could use lighter tank if pressure transfer to cavity
Only location in the world where this is possible
Ba Tag
Ba+ single ion tag demonstrated in traps
Issues are how to get ion to a trap and how to
convert Ba++ to Ba+
Current concept is to drift ion to an orifice where it is
extracted to low pressure, use ion guides to separate
ions from gas, and then transport to trap
System is similar to that used by molecular biologists
Ba Tag?
Short term tagging plan
Need to measure transport of Ba ions in Xe
EG what is the mobility?
Does Ba++ convert to Ba+?
Make new ion source to study these
A Tagged Ba++ Source?
To measure the overall efficiency of a barium tag a tagged
source would be valuable
Current concept is to use 252Cf source
Ba is at high mass fragment peak
Fraction of Ba is well known
Deposit on Si counter to tag based on light mass signal
Expect fragments stopping in Xe to end at ++ state
Possible short term use
Move XEL into Cryopit
Include a Ba tag
Demonstrate proof of principle for a detector with
Ba tag looking at 2n decay
Current location (above ground) has substantial pileup issues