XENON Collaboration (Talk 2) SAGENAP
Backgrounds / DM Sensitivity /
DOE Institutions
Rick Gaitskell
Brown University, Department of Physics
see information at
http://www.astro.columbia.edu/~lxe/XENON/
http://xenon.brown.edu/
Gaitskell
Summary - XENON Dark Matter Experiment
•Purpose of this second presentation is
o Summarize
o Outline
Radioactive Backgrounds of XENON10 module
involvement of DOE Groups in XENON Collaboration
• Brown University (DOE HEP/Particle Astro)
• Princeton University (DOE HEP)
• Lawrence Livermore National Laboratory
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <2>
XENON Backgrounds
Gaitskell
Summary of XENON10 Backgrounds
Current Monte Carlos have considered the following sources of backgrounds
• Gamma / Electron Recoil Backgrounds
o
Gammas inside Pb Shield
• PMT (K/U/Th/Co)
• Vessel: Stainless Steel (Co)
• Contributions from Other Components
Xe Intrinsic Backgrounds (incl. 85Kr)
o External Gammas - Pb Shield
o Rn exclusion
o Detector Performance/Design
o
• Gamma Discrimination Requirements
• Use of LXe Outer Veto vs xyz cuts
• Neutron Backgrounds
Internal Sources: PMT (a,n)
o External: Rock (a,n): Poly Shield
o Punch-through neutrons: Generated by muons in rock
o
• Requirements for Active Muon Shield
o
Neutrons arising from muon interaction in Pb shield
• Summary of changes for XENON100 detector & DM Sensitivity Goals
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <4>
DM Goals & Assumptions
• Goals
o
XENON10 - Sensitivity curve corresponds to 20 dm evts/10 kg/year
• Equivalent CDMSII Goal for mass >100 GeV
(Latest 2004 CDMSII result is x10 above this level)
• 30 live-days x 10 kg fiducial - Zero events - would reach XENON10
sensitivity goal 90% statistical goal, but we would like to do physics!
• Important goal of XENON10 prototype underground is to establish clear
performance of systems
o
XENON100 - Sensitivity curve corresponds to 20 dm evts/100 kg/year
• Simulations for XENON10 indicate can reach b/g necessary for this
sensitivity limit,
but with only 2 dm evts/10kg/year - no physics.
• Monte Carlo Inputs (stated here for the record, won’t discuss in detail)
o
o
Assume threshold for full discrimination 16 keVr
Liquid Xe (3 regions)
• LXe Fiducial (after any x-y-z position cuts) majority of inner Xe / LXe Inner (surrounded by Teflon wall - low Kr content) / LXe Veto (Xe outer layer, 5 cm simulated)
o
Nuclear/Electron Recoil Quenching Factor Primary Light (QFprimary)
• Zero Field (Conservative) QFp = 20%
• High Field (5 keV/cm) QFp = 50%
—
—
o
Background Discrimination
•
•
•
•
o
Electron recoil primary light yield reduced to 38-36%@ 1-5 kV/cm, (vs zero field) due to ionization component no longer recombining
Nuclear recoil primary light yield ~90%@5 kV/cm (vs zero field)
Electron Recoil assumed 99.5% (1 in 200) above threshold of 8 keVee/16 keVr
Monte Carlo results focus on rates for region 8-16 keVee (16-32 keVr)
External 5 cm LXe veto (Assumed 50 keVee threshold)
Multiple scatter cut within inner region (Dxy = 5cm, Dz = 1cm)
Radioactivity of Components
• Taken from direct measurements U/Th/K/Co (unless otherwise stated)
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <5>
XENON10 Schematic of Detector and Shield Design
Outer Poly (30cm)
Enclosed by
Muon Veto (Plastic Scint.)
Inner Poly (20cm)
Pb (22.5cm inc 5 cm ancient liner)
Stainless Steel Cryostat (62kg)
Teflon
PMTs (Hamamatsu R9288/8778)
Activity for R8778 used as baseline in
simulations
XENON10: 7 Inner PMTs
+ 16 outer veto PMTs
Xenon Gas
Liquid Xenon – Inner Region
(ø17.5 cm, h 15 cm, 11 kg)
Liquid Xenon – Veto Region
(thickness 5cm, 50 kg)
Copper (2.5cm)
Gaitskell Brown University
(parameters used in Monte Carlos)
XENON Collaboration / SAGENAP
April 2004 v03 <8>
DM Saying #2
The sensitivity of a direct detection dark matter search
experiment scales with the mass* …
The systematics, which ultimately limit the sensitivity,
scale with the surface area.
*Under scalar coupling assumption appropriate to scale to Ge equivalent
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <9>
XENON10 – Gamma/Electron Background Event Rates
• Gamma Background Event Rates (8 < E < 16keVee) for XENON10 Module
XENON10 Goal is 160 mdru gammas before electron recoil rejection
o XENON100 Goal (16 mdru) can also be achieved using anti-coin. LXe Veto and multiple scatters cut
o All rates quoted before assumed 99.5% electron recoil rejection vs nuclear recoil signal
o
Source
Inner Event Rate (only z cut)
(8 < E <16 keVee) [ mdru ]
Inner Event Rate with extra cuts:
Anti-Coincid. with LXe outer
+ single scatter cut
(8 < E <16 keVee) [ mdru ]
7 Inner PMTs
38
3.5
16 Outer PMTs
8.3
<0.1
HV Shaping Ring Resistors
6.8
1.6
Stainless Steel Cryostat
10
<0.1
6
6
Lead
-
-
(PMT Neutrons)
( 10-5 )
( 10-6 )
Total
69 mdru
11.1 mdru
85Kr
(@ 0.1 ppb)
Event Rate Tables for External Neutrons are dealt with in Appendix
Gaitskell Brown University
XENON Collaboration / SAGENAP
mdru = 10-3 evts/keVee/kg/day
April 2004 v03 <10>
Hamamatsu PMT Selection
Improvement in b/g’s of PMTs to ~20 mBq has
been impressive (driven by XMASS). PMTs for
XENON10/100 a realistic choice
• Hamamatsu Low Background PMTs
o
The isotopes contribute differently to event rate in (8<E<16keVee) window. For inner PMTs the following
concentrations (mBq/tube) of isotopes give the same event rates (238U/ 232Th/ 40K/ 60Co)
— All
Xe Events:
— Xe Fiducial Anti-Coincident, Single Scatter Events:
Model
R6041
R9288
Photo
(not
same
scales)
Dimension
& QE
ø5 cm x 4 cm
QE 5-8%
ø5 cm x 4 cm
QE 20%
R8520
(2.5
QE >20%
R8778
ø5 cm x 12 cm
QE 26%
Radioactive Background
[mBq/tube]
U Series
Gaitskell Brown University
Th Series
40K
360
90
5040
60Co
10
33.9 mBq – 238U equivalent
(Use of Kovar for most of base)
10
10
120
3
0
5
23.7 mBq – 238U equivalent
(expect further improvement)
13
4
60
Specifically designed for ops in LiqXe
TPC
Evolution of 6041
3
22.8 mBq – 238U equivalent
15
Base Components lower
activity, than these #’s
Comment
680 mBq – 238U equivalent
(Dominated by glass seal at base)
cm)2x3.5cm
(good dyn optics)
10 / 6 / 319 / 23 mBq
10 / 10 / 461 / >80 mBq
3
XENON Collaboration / SAGENAP
Square/quad anode
good fill factor (66.2%).
Columbia tested at 150K/4 atm
Designed for XMASS.
Coverage Area: 49.7%
Columbia tested at 150K/4 atm
April 2004 v03 <11>
Kr removal (Princeton/Shutt) Charcoal Column Separation
• 85Kr. 687 keV endpoint b decay
o
Rate: 280 kBq/Kg(Kr).
• XENON100: need <~0.1 ppb Kr/Xe.
• Industry (SpectraGas) can produce ≈ 10 ppb Kr/Xe.
• Investigating Chromatographic separation with
activated charcoal
o
Xe
Kr
Separate NSF funding at Princeton
• Separation demonstrated with 60 gm charcoal
column.
Kr separation ≈ 99.9 % (Preliminary)
• Full processing system now being tested.
• Projected performance, 1 kg charcoal column:
o
o
o
1.8 kg Xe/day
Purification ≈ 103 (PRELIMINARY)
Use 14 stp m3 He/ kg Xe processed.
• High purity system: completed Summer 05.
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <12>
Material Radioactivity Screening Program
• First step (~ 6 months):
o
SOLO (Soudan Low Background Screening Facility - coordinated by Brown): gamma screening for
Majorana, CDMS & XENON
• Second step:
Enlarge SOLO facility with additional ULB, 100 % eff HPGe detector,
o Read-out electronics + software (U Florida) and operate facility jointly
o
• Future:
o
Soudan Low Background Lab proposal - SOLO will be integrated into the proposed larger Low
Background Lab
• Priority of screening (over ~ 1 year):
PMTs: inner parts, ancillary parts, glass
o Resistive material (RuO2) and substrate
o PFTE of inner chamber
o Charge collection wires, material for grid, material for ring supporting PMTs
o Shielding materials, cables, connectors, insulation material, outer vessel
o
• Results from screening will be integrated into Monte Carlo background studies
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <13>
XENON10 and beyond - Conclusion - Backgrounds
• For XENON10 current Monte Carlos indicate ~10x safety margin vs XENON10 Goal
o
Assuming 99.5% electron recoil rejection, XENON10 able to achieve XENON10 goal (20 dm evts/10kg/year)
• Preliminary discrimination tests will be performed above ground
• The rejection will need to be checked & optimized using underground operation
o
Use of outer LXe veto region
• Including 5 cm outer LXe veto projects backgrounds (<2 bg evt/10 kg/year) allowing XENON10 to achieve XENON100
sensitivity goal
o
Note that WIMP event rate in XENON10 module for XENON100 sensitivity goal will be only 2 WIMPs per year limited discovery potential in this lower region
• External Pb/Poly/Muon Veto Shield Design & Depth Requirements
o
Propose construction of poly/Pb shield capable of housing XENON10 or XENON100 module
• Standard design suppresses external gammas and neutrons to below XENON100 required goals
o
Muon Veto
• Muon veto required to tag neutrons generated by muons in Pb shield
• XENON10 & 100 goals achievable at >=2.1 kmwe with 95% veto efficiency (see full tables in Appendix)
o
High Energy Punch-through Neutrons from rock - Site Dependent
• 2.1 kmwe (Soudan) Shallow Site will severely limit progress beyond XENON10 goal (exp. sig. 0.3x WIMP goal)
• ~3.7 kmwe (Gran Sasso) provides 25x drop in flux, which is 0.1x XENON100 goal, ~XENON1T goal
• ~6.2 kmwe Sudbury/Homestake (Deep) provides additional 25x drop in flux, well below all goals
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <14>
DOE Group Involvement
Gaitskell
Brown/DOE Participation in the XENON Project
• Brown HEP/Particle Astrophysics Group with DOE support
o
Senior Physicist: R. Gaitskell (Prof)
• >10 years DM R&D + Underground Operation Experience with CDMS I+II Experiments
o
Graduate Students:
• P. Sorensen (~2 years experience on project) / L. De Viveiros (~1 year experience on project)
• Contribution to XENON Project
Alternative Photo-detector Evaluation (Micro-channel Plate / (APD))
o DAQ Development for 10 kg Prototype & XENON10 detector
o Low Background Shield and Muon Veto for Underground Operation
o
• Monte Carlo Studies of radioactive backgrounds for XENON10
• Design/Construction
o
Background Screening (in conjunction with Florida U) of gamma activity of components
• Current operation of SOLO (Soudan Low Background Gamma Counting Facility) -> New Soudan Low
Background Lab
o
Underground Construction / Operations Experience
• CDMS @ Soudan
o
Participation in management of the multi-institutional XENON project
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <17>
Proposed DOE Support for Brown Group
• Brown Group on XENON is currently PI (Gaitskell) + 2 grads
o Currently
supported through combination of OJI + Start-up
(funds shared with existing CDMSII program, 2 senior grads)
• Need to add PostDoc at Brown to XENON program
o Would
have direct responsibility for DAQ and Shield on Project
• Operations Cost
o Underground
Site / Travel
• Propose Equipment Purchase for Underground Phase XENON10
o Shields
(Jul 2005 ->) $349k
• Shield Spec would satisfy both XENON10 & XENON100 requirements
o DAQ
(Jul 2005 ->) $96k
• Phased introduction - start with XENON10 system & then upgrade to XENON100
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <18>
Shield Cost XENON10 / 100
• Propose to DOE the construction of a shield which will accommodate
either XENON10 and then XENON100 module
o Inner
cavity ø 67 cm x h 100 cm
o From inside to out inner poly / Ancient Pb / Pb / Outer Poly : 20 / 5 / 18 / 30 cm
o Purchase & Construction Jul 2005–Mar 2006
Inner Poly (20 cm / 0.7 t)
$12k
Inner Ancient Pb (5 cm / 4.8 t)
$48k
Outer Pb (18 cm / 23 t)
$66k
Outer Poly (30 cm / 5 t)
$69k
Radon Seal + Gas Handling
$5k
Support Structure / Access Mechanism
$30k
Engineering Design / Machining
$65k
Muon Veto Plastic Scin + PMT
$119k
(assumes >95% efficient)
TOTAL
$349k
Cost of shield that can accommodate XENON10 only would be ~66% of above #’s
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <19>
DAQ Cost XENON10 / 100
• Propose to DOE for phased DAQ for XENON10 or XENON100 module
o ADCs
and associated electronics for Inner LXe PMTs, Outer LXe Veto PMTs and
also Muon Veto (Plastic Scint) + associated electronics/trigger logic +Processing
Farm for Events
o Inner PMT/Outer PMT/Muon Veto # XENON10: 7 / 16 / 24 XENON100: 37 / 48 / 24
XENON10
XENON100
Fast ADCs (1 ns sampling) Inner PMTs
$28k
$40k
Slow ADCs (100 ns) Inner/Outer/Veto PMTs
$19k
$50k
Crates / Communication Buses
$12k
$24k
Shaping Amps / Trigger Logic / DAQ Ctl
$19k
$28k
DAQ / Analysis Farm + Storage Computing
$18k
$32k
TOTAL
$96k
$174k
Multiplexing of ADCs reduces unit count / Units from XENON10 can be used in XENON100
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <21>
Princeton/DOE Participation in the XENON Project
• Princeton HEP Group with DOE support:
Senior Physicists: K. McDonald (Prof), C. Lu (Research Staff).
o HEP Group Technical Staff: Mechanical Engineer, 3 Machinists, 2 Electronics Technicians.
o
• Extensive Group experience in fabricating major systems for “remote” projects: miniBooNE PMT array, BaBar drift
chamber and LST, Belle glass RPC’s & SVT readout, L3 EMcal readout, …..
• Projected contributions to the XENON project:
o
CsI photocathode fabrication
• 12” and 36” vacuum deposition systems
• Characterization (absolute QE down to 100 nm, normalized to NIST calibrated diode)
o
Option for x-y readout via gas gain on wires
• Minimization of detector activity
o
Option for lower-background surface test facility
• ~300 ton water tank / test of feasibility of water shield at depth
o
Design and fabrication of infrastructure for underground operation
• Previous group experience of remote operation
Machining/ fabrication for 10 & 100 kg Xe modules (multi-module detector array)
o Participation in management of the multi-institutional XENON project
o
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <23>
LLNL/DOE Participation in the XENON Project
• LLNL Neutrino Detector Group with DOE support
o
Senior Physicists: Adam Bernstein (Staff), Chris Hagmann (Staff)
• Low energy neutrino detection, axion experiment.
o
Engineers/PostDocs: Norm Madden , Celeste Winant (PostDoc)
• Contribution to XENON Project
o
External Voltage Divider & Readout Circuits for PMTs
• Benefits include reduction in power consumption, heat load and radioactive burden from electronics
o
HV system / feed-throughs for Drift field in liquid Xe
• Drfit Field: 5 kV/cm applied field, 10-30 cm drift
o
Modeling of low energy quenching factor for nuclear recoils in liquid Xe
• Exploits modified TRIM code (existing studies)
o
Overlap with LLNL neutrino detection program
• Compact detectors for nuclear reactor n monitoring - nuclear fuel assay / NA-22 Office of Nonproliferation Research
and Engineering
• Overlap in detector hardware, readout / leverage of ongoing DOE programs
o
Participation in management of the multi-institutional XENON project
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <24>
Proposed DOE Support for LLNL Group
• Group Headed by Chris Hagmann / Adam Bernstein
o Will
seeking Lab support for their direct salary component for XENON
• PostDoc + Engineer
o PostDoc
(Celeste Winant, hired) full-time on project
o Engineer (Norm Madden) part-time on XENON
o $200k p.a.
• Equipment
o Testing
of PMT biasing schemes and resistor loadings
o Field cage design and testing
o $50k p.a.
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <25>
XENON Backgrounds
APPENDIX
Gaitskell
DEPTH REQUIREMENTS
NEUTRONS - MUONS IN Pb SHIELD
NEUTRONS - MUONS IN ROCK
Gaitskell
Appendix: Dark Matter Depth Requirements
•
Site Depth Requirement
o
•
Dominated by need to reduce high energy (HE) neutrons (50-600 MeV), generated by
muons, that cannot be moderated directly using poly
Shallow ~2000 mwe (e.g. Soudan, 1 muons/m2/minute)
o
o
Satisfactory for 10 kg scale experiments (s~10-44 cm2) (HE neutrons & Veto requirements)
To realize full potential of 100 kg-1 tonne experiments would require large additional active
shield (>2 m thick) in order to tag HE neutrons
• Significant risk associated with systematic failure to veto muon/HE neutron
o
•
Intermediate ~3800 mwe
o
o
o
o
•
Satisfactory for cosmogenic activation
Factor ~25x reduction in HE neutrons compared to shallow
Significant comfort factor for 100 kg scale experiment (s~10-45 cm2)
1 tonne experiments could function wrt to HE neutrons from muons (s~10-46 cm2) using
multiple scatter/capture ID of residual HE neutrons (prob. no thick active shield)
Muons passing through detector array can be vetoed by muon veto
(>99% being achieved)
Deep ~6000 mwe (Further factor ~50x reduction in muon/HE neutrons)
o
Eliminates any risk from HE neutrons/muons allowing (s~10-46 cm2) sensitivity
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <29>
Neutrons From Pb Shield, Tagging with Veto
• REQUIRE MUON
VETO EFFICIENCIES
Designed to tag
muons that create
neutrons in Pb shield
o Table shows required
muon tagging
efficiency to meet
goals
o Increasing poly within
Pb shield from 10 cm
to 20 cm reduces
neutron flux from
muons in Pb by ~10x
o Must also consider
use of veto for punchthrough neutrons
o Depth requirement
also constrained by
punch-through
neutrons
o
NR Goal
Goal
Rate @ 16 keVr
1/3 of total sens.
Muon Rate
Soudan
2.1 kmwe
1
(relative)
(20 cm inner poly)
Gran
Sasso
x1/25
50%*
(1:2)
XENON100
10 µdru
95%
(1:20)
Min µVeto
(1:~1)
XENON1T
1 µdru
99.5%
(1:200)
87%
(1:8)
(also CDMSII goal)
6.2 kmwe
3.7 kmwe
100 µdru
XENON10
Sudbury
x1/525
Min µVeto
Min µVeto
(Raw Rate below goal)
(Raw Rate below goal)
Min µVeto
(Raw Rate below goal)
Min µVeto
(Raw Rate below goal)
* Reference number for Soudan from Monte Carlo results from CDMSII (Kamat CWRU)
- 2 mdru NR @ 15 keVr, for 23 cm Pb shield & 10 cm inner poly
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <30>
Punch-through High Energy Neutrons From Rock
• Muon Veto
High Energy Neutrons
20–600 MeV generated
by muons in rock of
cavern
o Majority leave no
signal in muon veto
(some prospect for
tagging shower,
and/or possibly
neutron)
o Poly shield has
relatively little effect
on flux
o Pb shield causes
neutron
multiplication!
o
NR Goal
Goal
Rate @ 16 keVr
1/3 of total sens.
Muon Rate
-> Neutrons
Soudan
2.1 kmwe
Gran
Sasso
3.7 kmwe
Sudbury
6.2 kmwe
1
x1/25
x1/525
100 µdru
x1
x1/25
x1/525
XENON100
10 µdru
x10
x1/3
x1/53
XENON1T
1 µdru
x100
x3
x1/5
XENON10
(also CDMSII goal)
* Numbers show expected Nuclear Recoil (NR) single scatter event rate originating from high
energy neutrons as a fraction of nominal NR goal (which is x1/3 of WIMP NR goal)
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <31>
High Energy (E>20 MeV) Neutrons from Muons
• High Energy Neutron Rates can be decreased by controlling the Muon Flux, either
by a very efficient Muon Veto or by going to greater depths
•Neutron production ~ Muon Flux
oWith
slight modification for hardening of
muon spectrum †
mean(Em)~ Depth0.47
Soudan
Si te
* Not exca vat ed
(Multiple le vels given in f t)
Relative Relative
Muo n Neutron
Flux
Flux
>10 MeV
WIPP (2130 ft)
Soudan
Kamioke
Boulby
Gran Sasso
Frejus,
Homestake (4860 ft)
Mont Blanc
Sudbury
Homestake (8200 ft)
x 65
x 30
x 12
x4
x 45
x 25
x 11
x4
x1
x1
x 6-1
x 25-1
x 50-1
x 6-1
x 25-1
x 50-1
†Aglietta et.al. Nuove Cimento 12, N4, page 467
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <34>
High Energy Neutron Background
• Cosmic Ray Muons generate High Energy Neutrons (10-2000 MeV) in Rock
• MC Simulations with a typical High Energy Neutron (E = 300MeV) show that the Poly-PbPoly Shield mentioned previously is very inefficient in moderating these Neutrons
Conventional Shield: Only ~20% Neutron Flux Reduction
o If experiment is to be conducted at shallow site, we are investigating use of water shield with
minimum 3m shielding in all direction - provides factor x1/100 reduction in neutron flux
o
0.1 n/MeV/primary
Neutron flux / incoming neutron
10
Energy Histogram of Neutrons After:
30cm Poly + 23cm Pb + 30cm Poly
3m Water
0.01 n/MeV
/primary
1
Poly
(30cm)
Pb
(23cm)
Poly
(30cm)
0.1
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <35>
FURTHER DETAILS OF
RADIOACTIVITY
WITHIN SHIELD
Gaitskell
The simulation is run with a source that simulates the emission lines of the 20 physical PMTs. For this
simulated PMT, we used the Hammamatsu R8778 tube.
2D “Hitogram” – Energy vs. Depth
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <38>
Gamma Background (Inner & Outer PMTs)
• The Inner PMT radiation is 4x below XENON10 Target and can be further reduced to 40x below XENON10 goal with the use
of a Outer LXe Veto Region Anti-coincidence cut and Multiple Scatters cut
• Hamamatsu 8778 PMTs - Measured Activity per PMT: 238U/ 232Th/ 40K/ 60Co = 13 / 4 / 60 / 3 mBq
o
o
o
Prototypes of alternative low background Hamamatsu PMTs within 1-1.5x of this
7 Inner Chamber PMTs / 16 Veto Region PMTs
Events Detected in the Inner Chamber – DRU Event Rates averaged over the range 8-16 keVee
7 Inner PMTs
XENON10 Target
16 Outer LXe Veto PMTs
XENON10 Target
XENON100 Target
XENON100 Target
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <39>
PMT Gamma Background - Spatial Distribution
• The Spatial Distribution of Background Events shows that the majority of low energy events are
concentrated in the surface of the Inner LXe due to placement of the Inner PMTs
• 7 Inner Chamber PMTs + 16 Veto PMTs -- after Xe Veto Region Coincidence Cut
o
Requires only top 2.5 cm cut for rates to be below XENON10 background goal in the entire energy spectrum after veto
and multiple-scatter cut – overall background rate can be reduced by removing the top region from the fiducial detector region.
Anti-Coincident Inner Events
(8 < E < 100keV)
Gaitskell Brown University
XENON Collaboration / SAGENAP 040415
April 2004 v03 <40>
Inner Chamber PMT Gamma Background
• Inner PMTs -- Hamamatsu 8778 (232Th/238U/40K/60Co):
o
Spatial Distribution and Energy Histogram for Events Detected in Inner Chamber
XENON10 Target
XENON100 Target
Gaitskell Brown University
XENON Collaboration / SAGENAP 040415
April 2004 v03 <41>
HV Shaping Ring Resistors
• Background Event Rate due to 10 Resistors below XENON10 Target except in area immediately
around resistor (distance < 1cm)
• Further Background Reduction can be achieved with a x-y cut in around the resistors
o
10 Resistors in line run down the side of the inner chamber for the length of the inner Liquid Xenon region
o
Typical Resistor Background: 238U: 0.24mBq / 232Th: 0.22mBq / 40K: 0.52mBq / 60Co: <0.02mBq
Anti-Coincident Inner Events (8 < E < 100 keV)
Spatial Distribution – Top View
Inner Events (8 < E < 28 keV)
Energy Histogram
XENON10 Target
XENON100 Target
Gaitskell Brown University
XENON Collaboration / SAGENAP 040415
April 2004 v03 <44>
Stainless Steel Gamma Background
• Gamma Background from Stainless Steel Cryostat below XENON100 target - Liquid
Xenon Veto provides excellent shield against radiation from Cryostat
o
Double-walled Cryostat, each wall 1/8” thick, total 62kg
o
Activity (per kg): 60Co: 23mBq / 238U: 3.5mBq / 232Th: 2.7mBq
Anti-Coincident Inner Events (8 < E < 100keV)
Spatial Distribution
Inner Chamber Events (8 < E < 28 keV)
Energy Histogram
XENON10 Target
XENON100 Target
Gaitskell Brown University
XENON Collaboration / SAGENAP 040415
April 2004 v03 <45>
Effect of 5 cm LXe Veto Region - on Stainless Steel Activity
• The Multiple Scatters Cut is does not guarantee that the background rate falls below target throughout the entire Inner Chamber.
o
The background rate can be reduced by fiducializing the detector – cut events from the outermost layer of the Inner Chamber and the background rate falls well below
target for the entire fiducial region.
With Xe Veto
Without Xe Veto
Anti-Coincident Single Scatter Inner Events
Single Scatter Inner Events
Gaitskell Brown University
XENON Collaboration / SAGENAP 040415
April 2004 v03 <47>
PMT Neutron Background
• ( ,n) Neutron Activity for the Hamamatsu R8778 PMT: ~0.11 neutrons/PMT/year
Estimated for 13mBq of 238U and 4mBq of 232Th
o QF of 50% assumed for results below – Energy Histogram scaled to keVee
o Background Rates are below XENON100 Target by 4 orders of magnitude
o
Inner Events Detected
XENON10 Target
XENON100 Target
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <48>
Outer LXe Veto vs Single Xe with xyz Cut
• Simulation Results based on use of 5 cm LXe outer veto, with separate inner LXe
volume
• Outer LXe veto could be replaced by single larger LXe region. Then perform additional
xyz cuts
Outer LXe Veto is more conservative approach
o Need to establish that radial cuts (outer ~5 cm) will work at necessary level in single Xe
volume (z, drift depth determination looks very robust)
o Xe used for electron drift volume requires much higher purity levels
o
• Use of separate inner/outer volumes allows easier management of component locations
o
Outer LXe veto has much lower light collection efficiency requirements
• Although amount of Xe used in outer veto is >~2.5x that of simple Xe inner expansion
Outer LXe veto provides additional environmental stabilization/buffer for thermal gradients
on inner bath
o Inner LXe region will have lower event rate “quieter” - reduces influence of systematics
o Once data from XENON10 is available the use of veto in XENON100 module will also need to
be evaluated
o
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <51>
Radon In Mine Air
• The Pb shield will be enclosed in a thick mylar (250 µm) air tight
enclosure
o Flushed
by LN2 boil off
o This system has been tested in Soudan (SOLO) gamma background screening
facility
• Ambient Rn ~200-500 Bq/m3 air in mine
• Peak search (Rn daugheters) in Ge dets - undetectable for equivalent of
0.01 /keV/kg/day (low energies) sensitivity.
• This would put activity in inner LXe below XENON1T goal
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <56>
210Pb Radiation - Gamma & Electron Background
• Pb Shielding Radiation –Effect of intrinsic 210Pb: 30 Bq/kg
(Standard Low Activity - not ancient Pb)
o
The low rate is due to the high efficiency of the Liquid Xenon Veto Region in Shielding the
Inner Chamber from External Gammas
Events Detected in Inner Chamber
XENON10 Target
XENON10 Target
XENON100 Target
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <59>
210Pb without Liquid Xenon Veto Region
• Without outer LXe veto (5 cm) region would increase the background activity above
acceptable levels -- up to 2 orders of magnitude in the case of the Pb shield radiation:
o
Pb Radiation - Simulations done with Pb liner 2.5 cm thick (830kg), 30 Bq/kg
Pb Radiation (Without Veto Region)
Events Detected in Inner Chamber
XENON10 Target
XENON100 Target
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <60>
(a,n) Neutron from Rock
• (a,n) Neutron from Rock peak at 3MeV
• Shielding: 35cm Poly + 22.5cm Pb + 20cm Poly
MC Simulations of moderating (alpha,n) Neutrons (T<100 keV below candidate recoil threshold)
o Flux Reduction ~5 orders of magnitude for 50cm of Poly for total spectrum
o Example for 3 MeV (more penetrating at higher energies due to lower elastic c-s in poly)
o
Relative Neutron Flux
For incoming 3 MeV Neutrons (Most Penetrating)
100
Neutron (alpha,n) Spectrum From Rock
Pb
(22.5 cm)
Poly
(35 cm)
Poly
(20 cm)
Flux (arb units)
Neutrons / Incoming Neutron
1000
Integrated Flux (>100 keV) ~4x10^-6 /cm^2/s
(Soudan)
100
10
1
0
10-4
1
2
3
4
5
6
Energy (MeV)
0
Gaitskell Brown University
z [cm]
70
XENON Collaboration / SAGENAP
April 2004 v03 <63>
Kr REMOVAL
Gaitskell
Liquid Xe Intrinsic Background – 85Kr (dominant concern)
•
contamination in Xenon – b decay (Q~687 keV)
Commercially Grade Purification Methods reach 10 ppb contamination
Required concentration to achieve XENON10 goal: <~1 ppb
85Kr
o
o
o
85Kr
events in LXe Veto Region – minimal contribution to events in inner LXe
Anti-coin, Single Scatter Inner Events
due to 85Kr Decays in Inner Chamber
Events Detected in Inner Chamber
due to 85Kr Decays in Veto Region
XENON10 Target
10ppb – 0.6 dru
XENON10 Target
1ppb – 60 mdru
XENON100 Target
XENON100 Target
10ppt – 0.6 mdru
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <66>
Kr removal (Princeton/Shutt) Charcoal Column Separation
• 85Kr. 687 keV endpoint b decay
o
Rate: 280 kBq/Kg(Kr).
• XENON100: need <~0.1 ppb Kr/Xe.
• Industry (SpectraGas) can produce ≈ 10 ppb Kr/Xe.
• Investigating Chromatographic separation with
activated charcoal
o
Xe
Kr
Separate NSF funding at Princeton
• Separation demonstrated with 60 gm charcoal
column.
Kr separation ≈ 99.9 % (Preliminary)
• Full processing system now being tested.
• Projected performance, 1 kg charcoal column:
o
o
o
1.8 kg Xe/day
Purification ≈ 103 (PRELIMINARY)
Use 14 stp m3 He/ kg Xe processed.
• High purity system: completed Summer 05.
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <68>
XENON100 MODULE
BACKGROUND SIMULATION
SUMMARY
Gaitskell
XENON100 Goals - Summary
• MC Background Studies show that the baseline design permits XENON100 to reach the XENON1T (20
events/1000 kg/year) sensitivity goal of 1.6 mdru (after 99.5% electron recoil discrimination) - however,
single 100 module would see only 2 evts/year.
• The low background rate is achieved by additional fiducialization of the inner LXe detector, i.e. cutting
events from the top 5cm, bottom 2.5cm, and a radial cut 2.5cm thick, from the outside, + 5 cm outer veto
o
o
XENON100 simulations use 55x 14mBq Inner PMTs + 64 Veto Region PMTs
The MC results depicted below are Single Scatter, Xe Veto Anti-Coincident Events (Veto Region = 5cm)
Spatial Distribution of Inner Chamber Events
(log10)
Energy Histogram of Events Detected
in Fiducial Inner Detector Volume
XENON1T Target
Gaitskell Brown University
XENON Collaboration / SAGENAP
April 2004 v03 <70>
DAQ SUMMARY
Gaitskell
DAQ System - XENON10
150
mV
Sample Pulse –- Max. Drift Distance: 15cm -> 75µs
100
50
0
0
25
μs
50
100ns/sample
2.4 ksample/ch
75
Integrator
SlowADC
Integrator
SlowADC
1ns/sample
120ksample/ch
84 MB/s
FastADC
400 MB/s
FastADC
Integrator
SlowADC
Integrator
SlowADC
Integrator
SlowADC
Integrator
SlowADC
Integrator
SlowADC
84 MB/s
PC#2 – G5 XRaid
1-3 TB Storage
FastADC
7 Inner Xe
PMTs
PC#1 – G4 XServer
Data Acqusition
Event Compression
FastADC
FastADC
FastADC
Gbit Ethernet
N-fold coincidence
Global Trigger
PXI Bus
Discrim. & Stretch
Optional Anti-coincidence
16 Outer Xe
PMTs
Gaitskell Brown University
G5 XServer Cluster
Offline Data Analysis
G5 Dual 2Hz Processor Node
SlowADC
x2 multiplex
G5 Dual 2Hz Processor Node
G5 Dual 2Hz Processor Node
x4 multiplex
24 Muon Veto
Plastic Scin PMTs
cPCI Bus
FastADC
SlowADC
(Used to Veto Event in PCs)
XENON Collaboration / SAGENAP
April 2004 v03 <72>
DAQ - Total Event Rates for Internal Components
Source
Inner Chaber
Total Event Rate for
DAQ
[ mHz ]
Veto Region
Total Event Rate for
DAQ
[ mHz ]
7 Inner PMTs
25
353
16 Outer PMTs
7.1
307
HV Shaping Ring
Resistors
3.6
12.5
Stainless Steel
Cryostat
8.6
333
0.3
<0.1
Lead
2.1
563
PMT Neutrons
10-8
10-8
Total
47.6 mHz
1.6 Hz
85Kr
Gaitskell Brown University
(@ 0.1 ppb)
XENON Collaboration / SAGENAP
April 2004 v03 <73>