gaitskell xenon collaboration (talk 2) - sagenap backgrounds / dm sensitivity / doe institutions...

Gaitskell

XENON Collaboration (Talk 2) - SAGENAP

Backgrounds / DM Sensitivity /

DOE Institutions

Rick Gaitskell

Brown University, Department of Physics

see information athttp://www.astro.columbia.edu/~lxe/XENON/

http://xenon.brown.edu/

Gaitskell Brown University XENON Collaboration / SAGENAP April 2004 v03 <2>

Summary - XENON Dark Matter Experiment

•Purpose of this second presentation is

oSummarize Radioactive Backgrounds of XENON10 module

oOutline involvement of DOE Groups in XENON Collaboration• Brown University (DOE HEP/Particle Astro)• Princeton University (DOE HEP)• Lawrence Livermore National Laboratory

Gaitskell

XENON Backgrounds


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

o Xe Intrinsic Backgrounds (incl. 85Kr)o External Gammas - Pb Shieldo Rn exclusiono Detector Performance/Design

• Gamma Discrimination Requirements• Use of LXe Outer Veto vs xyz cuts

• Neutron Backgroundso Internal Sources: PMT (,n)o External: Rock (,n): Poly Shieldo Punch-through neutrons: Generated by muons in rock

• Requirements for Active Muon Shieldo Neutrons arising from muon interaction in Pb shield

• Summary of changes for XENON100 detector & DM Sensitivity Goals


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

systemso 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.

CDMS II goal

XENON10

XENON100

Edelweiss

XENON1T

• Monte Carlo Inputs (stated here for the record, won’t discuss in detail)o Assume threshold for full discrimination 16 keVro 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%

— 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)

o Background Discrimination• 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 (xy = 5cm, z = 1cm)

o Radioactivity of Components• Taken from direct measurements U/Th/K/Co (unless otherwise stated)


XENON10 Schematic of Detector and Shield Design

Inner Poly (20cm)

Pb (22.5cm inc 5 cm ancient liner)

Stainless Steel Cryostat (62kg)

PMTs (Hamamatsu R9288/8778)Activity for R8778 used as baseline in simulationsXENON10: 7 Inner PMTs + 16 outer veto PMTs

Copper (2.5cm)

Teflon

Liquid Xenon – Veto Region (thickness 5cm, 50 kg)

Xenon GasLiquid Xenon – Inner Region(ø17.5 cm, h 15 cm, 11 kg)

Enclosed byMuon Veto (Plastic Scint.)

Outer Poly (30cm)

(parameters used in Monte Carlos)


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


XENON10 – Gamma/Electron Background Event Rates

SourceInner 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 <0.185Kr (@ 0.1 ppb) 6 6

Lead - -

(PMT Neutrons) ( 10-5 ) ( 10-6 )

Total 69 mdru 11.1 mdru

• Gamma Background Event Rates (8 < E < 16keVee) for XENON10 Moduleo XENON10 Goal is 160 mdru gammas before electron recoil rejectiono XENON100 Goal (16 mdru) can also be achieved using anti-coin. LXe Veto and multiple scatters cuto All rates quoted before assumed 99.5% electron recoil rejection vs nuclear recoil signal

mdru = 10-3 evts/keVee/kg/dayEvent Rate Tables for External Neutrons are dealt with in Appendix


• Hamamatsu Low Background PMTso 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: 10 / 6 / 319 / 23 mBq— Xe Fiducial Anti-Coincident, Single Scatter Events: 10 / 10 / 461 / >80 mBq

Hamamatsu PMT Selection

ModelPhoto(not

same scales)

Dimension& QE

Radioactive Background

[mBq/tube]

Comment

U Series Th Series 40K 60Co

R6041 ø5 cm x 4 cmQE 5-8%

680 mBq – 238U equivalent

(Dominated by glass seal at base) Specifically designed for ops in LiqXe TPC

360 90 5040 10

R9288 ø5 cm x 4 cmQE 20%

33.9 mBq – 238U equivalent

(Use of Kovar for most of base) Evolution of 6041

10 10 120 3

R8520 (2.5 cm)2x3.5cmQE >20%

22.8 mBq – 238U equivalent Square/quad anode

good fill factor (66.2%).

Columbia tested at 150K/4 atm15 3 0 5

R8778ø5 cm x 12 cm

QE 26%(good dyn optics)

23.7 mBq – 238U equivalent(expect further improvement)

Designed for XMASS.

Coverage Area: 49.7%

Columbia tested at 150K/4 atm13 4 60 3

Improvement in b/g’s of PMTs to ~20 mBq has been impressive (driven by XMASS). PMTs for XENON10/100 a realistic choice

Base Components lower activity, than these #’s


Kr removal (Princeton/Shutt) Charcoal Column Separation

• 85Kr. 687 keV endpoint decayo 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 charcoalo Separate NSF funding at Princeton

• Separation demonstrated with 60 gm charcoal column.

Kr separation ≈ 99.9 % (Preliminary)

Kr Xe

• Full processing system now being tested.• Projected performance, 1 kg charcoal column:

o 1.8 kg Xe/dayo Purification ≈ 103 (PRELIMINARY)o Use 14 stp m3 He/ kg Xe processed.

• High purity system: completed Summer 05.


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:o Enlarge SOLO facility with additional ULB, 100 % eff HPGe detector, o Read-out electronics + software (U Florida) and operate facility jointly

• Future: o Soudan Low Background Lab proposal - SOLO will be integrated into the proposed larger Low

Background Lab

• Priority of screening (over ~ 1 year):o PMTs: inner parts, ancillary parts, glasso Resistive material (RuO2) and substrateo PFTE of inner chambero Charge collection wires, material for grid, material for ring supporting PMTso Shielding materials, cables, connectors, insulation material, outer vessel

• Results from screening will be integrated into Monte Carlo background studies


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 Requirementso Propose construction of poly/Pb shield capable of housing XENON10 or XENON100 module

• Standard design suppresses external gammas and neutrons to below XENON100 required goalso 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

DOE Group Involvement


Brown/DOE Participation in the XENON Project

• Brown HEP/Particle Astrophysics Group with DOE supporto Senior Physicist: R. Gaitskell (Prof)

• >10 years DM R&D + Underground Operation Experience with CDMS I+II Experimentso Graduate Students:

• P. Sorensen (~2 years experience on project) / L. De Viveiros (~1 year experience on project)

• Contribution to XENON Projecto Alternative Photo-detector Evaluation (Micro-channel Plate / (APD))o DAQ Development for 10 kg Prototype & XENON10 detectoro Low Background Shield and Muon Veto for Underground Operation

• 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 Labo Underground Construction / Operations Experience

• CDMS @ Soudan o Participation in management of the multi-institutional XENON project


Proposed DOE Support for Brown Group

• Brown Group on XENON is currently PI (Gaitskell) + 2 gradso 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 programo Would have direct responsibility for DAQ and Shield on Project

• Operations Costo Underground Site / Travel

• Propose Equipment Purchase for Underground Phase XENON10o Shields (Jul 2005 ->) $349k

• Shield Spec would satisfy both XENON10 & XENON100 requirementso DAQ (Jul 2005 ->) $96k

• Phased introduction - start with XENON10 system & then upgrade to XENON100


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 cmo 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(assumes >95% efficient)

$119k

TOTAL $349k

Cost of shield that can accommodate XENON10 only would be ~66% of above #’s


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


Princeton/DOE Participation in the XENON Project

• Princeton HEP Group with DOE support:o Senior Physicists: K. McDonald (Prof), C. Lu (Research Staff).o HEP Group Technical Staff: Mechanical Engineer, 3 Machinists, 2 Electronics Technicians.

• 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

o Machining/ fabrication for 10 & 100 kg Xe modules (multi-module detector array)o Participation in management of the multi-institutional XENON project


LLNL/DOE Participation in the XENON Project

• LLNL Neutrino Detector Group with DOE supporto 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 Projecto External Voltage Divider & Readout Circuits for PMTs

• Benefits include reduction in power consumption, heat load and radioactive burden from electronicso HV system / feed-throughs for Drift field in liquid Xe

• Drfit Field: 5 kV/cm applied field, 10-30 cm drifto 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 monitoring - nuclear fuel assay / NA-22 Office of Nonproliferation Research and Engineering

• Overlap in detector hardware, readout / leverage of ongoing DOE programso Participation in management of the multi-institutional XENON project


Proposed DOE Support for LLNL Group

• Group Headed by Chris Hagmann / Adam Bernsteino Will seeking Lab support for their direct salary component for XENON

• PostDoc + Engineero PostDoc (Celeste Winant, hired) full-time on projecto Engineer (Norm Madden) part-time on XENON o $200k p.a.

• Equipmento Testing of PMT biasing schemes and resistor loadings o Field cage design and testingo $50k p.a.

Gaitskell

XENON Backgrounds

APPENDIX

Gaitskell

DEPTH REQUIREMENTS

NEUTRONS - MUONS IN Pb SHIELDNEUTRONS - MUONS IN ROCK


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 Satisfactory for 10 kg scale experiments (~10-44 cm2) (HE neutrons & Veto requirements)o 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 Satisfactory for cosmogenic activation• Intermediate ~3800 mwe

o Factor ~25x reduction in HE neutrons compared to shallowo Significant comfort factor for 100 kg scale experiment (~10-45 cm2)o 1 tonne experiments could function wrt to HE neutrons from muons (~10-46 cm2) using

multiple scatter/capture ID of residual HE neutrons (prob. no thick active shield)o 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 (~10-46 cm2) sensitivity


Neutrons From Pb Shield, Tagging with Veto (20 cm inner poly)

• REQUIRE MUON VETO EFFICIENCIES

o 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 punch-through neutrons

o Depth requirement also constrained by punch-through neutrons

GoalNR Goal

Rate @ 16 keVr1/3 of total sens.

Soudan2.1 kmwe

Gran Sasso3.7 kmwe

Sudbury6.2 kmwe

Muon Rate(relative)

1 x1/25 x1/525

XENON10(also CDMSII goal)

100 µdru50%* (1:2)

Min µVeto (Raw Rate below goal)

Min µVeto(Raw Rate below goal)

XENON100 10 µdru95%

(1:20)Min µVeto

(1:~1)Min µVeto

(Raw Rate below goal)

XENON1T 1 µdru99.5% (1:200)

87%(1:8)

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


Punch-through High Energy Neutrons From Rock• Muon Veto

o High Energy Neutrons20–600 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!

GoalNR Goal

Rate @ 16 keVr1/3 of total sens.

Soudan2.1 kmwe

Gran Sasso3.7 kmwe

Sudbury6.2 kmwe

Muon Rate-> Neutrons 1 x1/25 x1/525

XENON10(also CDMSII goal)

100 µdru x1 x1/25 x1/525

XENON100 10 µdru x10 x1/3 x1/53

XENON1T 1 µdru x100 x3 x1/5

* 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)


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

†Aglietta et.al. Nuove Cimento 12, N4, page 467

Soudan

Site* Not excavated(Multiple levels given in ft)

RelativeMuonFlux

RelativeNeutron

Flux >10 MeV

WIPP (2130 ft) x 65 x 45Soudan x 30 x 25Kamioke x 12 x 11Boulby x 4 x 4Gran SassoFrejus,Homestake (4860 ft)

x 1 x 1

Mont Blanc x 6-1 x 6-1

Sudbury x 25-1 x 25-1

Homestake (8200 ft) x 50-1 x 50-1

•Neutron production ~ Muon FluxoWith slight modification for hardening of muon spectrum †

mean(E)~ Depth0.47


0.1 n/MeV/primary

0.01 n/MeV/primary

Energy Histogram of Neutrons After: 30cm Poly + 23cm Pb + 30cm Poly

3m Water

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-Pb-

Poly Shield mentioned previously is very inefficient in moderating these Neutronso 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

1

10

0.1

Poly(30cm)

Poly(30cm)

Pb(23cm)

Neu

tron

flux

/ in

com

ing

neut

ron

Gaitskell

FURTHER DETAILS OF RADIOACTIVITY WITHIN SHIELD


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


XENON10 Target

XENON100 Target

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 Prototypes of alternative low background Hamamatsu PMTs within 1-1.5x of thiso 7 Inner Chamber PMTs / 16 Veto Region PMTso Events Detected in the Inner Chamber – DRU Event Rates averaged over the range 8-16 keVee

XENON10 Target

XENON100 Target

16 Outer LXe Veto PMTs7 Inner PMTs


• 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.

PMT Gamma Background - Spatial Distribution

Anti-Coincident Inner Events(8 < E < 100keV)

040415


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

040415


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 regiono 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

040415


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 62kgo 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

040415


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.

Without Xe VetoSingle Scatter Inner Events

With Xe VetoAnti-Coincident Single Scatter Inner Events

040415


• ( ,n) Neutron Activity for the Hamamatsu R8778 PMT: ~0.11 neutrons/PMT/yearo Estimated for 13mBq of 238U and 4mBq of 232Tho QF of 50% assumed for results below – Energy Histogram scaled to keVeeo Background Rates are below XENON100 Target by 4 orders of magnitude

PMT Neutron Background

Inner Events Detected

XENON10 Target

XENON100 Target


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 cutso Outer LXe Veto is more conservative approacho 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

• Use of separate inner/outer volumes allows easier management of component locationso 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 expansiono Outer LXe veto provides additional environmental stabilization/buffer for thermal gradients

on inner batho Inner LXe region will have lower event rate “quieter” - reduces influence of systematicso Once data from XENON10 is available the use of veto in XENON100 module will also need to

be evaluated


Radon In Mine Air

• The Pb shield will be enclosed in a thick mylar (250 µm) air tight enclosure

o Flushed by LN2 boil offo 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


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

XENON10 Target

Events Detected in Inner ChamberXENON10 Target

XENON100 Target


XENON10 Target

XENON100 Target

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


(,n) Neutron from Rock

• (,n) Neutron from Rock peak at 3MeV• Shielding: 35cm Poly + 22.5cm Pb + 20cm Poly

o 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 spectrumo Example for 3 MeV (more penetrating at higher energies due to lower elastic c-s in poly)

Relative Neutron FluxFor incoming 3 MeV Neutrons (Most Penetrating)

Poly(35 cm)

Pb(22.5 cm)

Poly(20 cm)

Neu

tron

s / I

ncom

ing

Neu

tron

Neutron (alpha,n) Spectrum From Rock

1

10

100

1000

0 1 2 3 4 5 6

Energy (MeV)

Flux (arb units)

Integrated Flux (>100 keV) ~4x10^-6 /cm^2/s(Soudan)

z [cm]0 70

100

10-4

Gaitskell

Kr REMOVAL


XENON10 Target

XENON100 Target

XENON10 Target

XENON100 Target

10ppb – 0.6 dru

1ppb – 60 mdru

10ppt – 0.6 mdru

• 85Kr contamination in Xenon – decay (Q~687 keV)o Commercially Grade Purification Methods reach 10 ppb contamination o Required concentration to achieve XENON10 goal: <~1 ppbo 85Kr events in LXe Veto Region – minimal contribution to events in inner LXe

Liquid Xe Intrinsic Background – 85Kr (dominant concern)

Anti-coin, Single Scatter Inner Eventsdue to 85Kr Decays in Inner Chamber

Events Detected in Inner Chamberdue to 85Kr Decays in Veto Region


Kr removal (Princeton/Shutt) Charcoal Column Separation

• 85Kr. 687 keV endpoint decayo 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 charcoalo Separate NSF funding at Princeton

• Separation demonstrated with 60 gm charcoal column.

Kr separation ≈ 99.9 % (Preliminary)

Kr Xe

• Full processing system now being tested.• Projected performance, 1 kg charcoal column:

o 1.8 kg Xe/dayo Purification ≈ 103 (PRELIMINARY)o Use 14 stp m3 He/ kg Xe processed.

• High purity system: completed Summer 05.

Gaitskell

XENON100 MODULEBACKGROUND SIMULATION

SUMMARY


XENON1T Target

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 XENON100 simulations use 55x 14mBq Inner PMTs + 64 Veto Region PMTso The MC results depicted below are Single Scatter, Xe Veto Anti-Coincident Events (Veto Region = 5cm)

(log10)Spatial Distribution of Inner Chamber EventsEnergy Histogram of Events Detected

in Fiducial Inner Detector Volume

Gaitskell

DAQ SUMMARY


0 25 50 75μs

0

50

100

150

mV

DAQ System - XENON10

N-fold coincidence

Discrim. & Stretch

Global Trigger

7 Inner XePMTs

cPC

I B

us

SlowADCFastADC

100ns/sample2.4 ksample/ch 1ns/sample

120ksample/ch

16 Outer XePMTs

Optional Anti-coincidence

24 Muon VetoPlastic Scin PMTs

PC#1 – G4 XServerData Acqusition

Event Compression

PC#2 – G5 XRaid1-3 TB Storage

G5 XServer ClusterOffline Data Analysis

(Used to Veto Event in PCs)

SlowADCFastADC

SlowADCFastADC

SlowADCFastADC

SlowADCFastADC

SlowADCFastADC

SlowADCFastADC

PX

I B

us

G5 Dual 2Hz Processor Node



x2 multiplex

x4 multiplex

400 MB/s

Gbit Ethernet

84 MB/s

84 MB/s

Prim

ary

Seco

ndar

y

Terti

ary

Sample Pulse –- Max. Drift Distance: 15cm -> 75µs

Integrator

Integrator

Integrator

Integrator

Integrator

Integrator

Integrator

SlowADC

SlowADC


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

Resistors3.6 12.5

Stainless Steel Cryostat

8.6 333

85Kr (@ 0.1 ppb) 0.3 <0.1

Lead 2.1 563

PMT Neutrons 10-8 10-8

Total 47.6 mHz 1.6 Hz

gaitskell xenon collaboration (talk 2) - sagenap backgrounds / dm sensitivity / doe institutions...

Documents

n o external

o radioactivity of components

kevr o liquid xe

poly shield o punch

sagenap backgrounds

xenon10 sensitivity

active muon shield o

sensitivity goals