Searching for Dark Matter From XENON10 to LUXlux.brown.edu/talks/20090330_ldv_coimbratalk_v8.pdfDe...

De Viveiros - Brown University April 2009 v07 <1>

FCT - Universidade de Coimbra - Café com Física

Luiz de Viveiros

Brown University – Physics Department

Searching for Dark Matter

From XENON10 to LUX


Summary

Introduction to Dark Matter

Detecting Dark Matter with liquid Xe

The XENON10 Experiment

Design and Deployment

Results

The LUX Experiment

Building a better detector – make it big !

Increase sensitivity by ~100x

Initial run at surface: LUX0.1

XENON10

22 kgLUX

350 kg


Composition of the Cosmos

Dark Energy

73%

Dark Matter

23%

Free H and He

4%

Stars and Gas

0.5%

Heavy Elements (us)

0.03%

ΛCDM Model


Dark Matter Evidence: Galactic Velocity Measurements

Velocities of galaxies in galactic clusters Fritz Zwicky, 1936 – measurement of radial

velocities in Coma cluster

Using virial theorem, concluded that Mstars~ 0.5% Mcluster

Galaxy rotation curves Expect v ~ r -1/2 (outside bulge)

Observe v ~ constant => M(r) / r ~ constant=> Dark Matter “Halo”

halo

bulge

disksun

• data

– bulge, disk & halo

bulge disk

Spiral Galaxies

v ~ r–1/2

v ~ const

Bulk of luminous matter

M (r )

r

light

M(r)

r const (r rcore)

Coma cluster (image from SDSS)


Cosmic Microwave Background

WMAP 5-year results (2009) (+SN+BAO)

Best fit to Λ-CDM model gives density parameters:

Ωtotal = 1.02 ± 0.02, Ωm = 0.275 ± 0.015, Ωb = 0.0456± 0.0015

Matter (Ωm) – Baryonic Matter (Ωb) Discrepancy → Nonbaryonic Dark Matter

Best fit to Λ-CDM model

Temperature Fluctuation by Angular SizeCosmic Microwave Temperature Fluctuations

5-year map (dipole + galaxy removed)

〈T〉= 2.725 K


Dark Matter Candidate: WIMP

WIMPs: Stable (or long lived) particles, relics from the Big Bang

Supersymmetry independently predicts a massive, weakly interacting particle

The Neutralino ( χ ): Lightest Supersymetric Particle (LSP)

WIMPs (and neutrons) scatter elastically off nuclei

Photons and electrons scatter off atomic electrons

Recoil energy spectrum and rate dependent on local dark matter density ρ0 and velocity distribution

Galatic Dark Matter Relic Density ρ0 ≈ 0.3 GeV/cm3 ( 3 WIMPs / liter for Mχ = 100GeV/c2 )

Recoil energy ≈ few keV – tens of keV (require detectors with low threshold)

WIMPS and Neutrons

nuclear recoils

Photons and Electrons

electron recoils


Typical WIMP Recoil Signal

Calculated differential event rates for Xe and Ge targets mWIMP = 100 GeV/c2 and σWIMP = 7x10-46 cm2 (estimated LUX sensitivity)

Standard Halo parameters

Assumes spin-independent interaction

1 dru = 1 event / keV / kg / day

Thresh at 5 keVr

1 event / 3,000 kg-days

σWIMP = 7x10-46 cm2

(LUX extimated sensitivity)

Xe

Ge


WIMP signals in Xe: Light and Charge

Light (S1): UV Photons (175 nm) from Xe ScintillationWph = 21.6 eV

Enhanced by local recombination

Charge (S2): Electrons separated from Xe+ ions:W ~ 15.6 eV

Local recombination in densely ionized region suppressed with high electric fields

Neutrons, WIMPs => Slow nuclear recoils => strong recombination=> S1 preserved, but Ionization S2 strongly suppressed

γ, e-, μ, (etc) => Fast electron recoils=> Weaker S1, Stronger S2

e-

e- e-

e-

e-e-

e-

e-

Xe+Ionization

+ Xe

Xe2+

Xe** + XeXe*

Excitation

+ Xe

Xe2*

Singlet

3 nsTriplet

27 ns

2Xe 2Xe175 nm175 nm Similar mechanism

for all noble liquids.

Ar:

Singlet = 10 ns

Triplet = 1500 ns

λ = 128 nm

Nuclear / Electron Recoil


Dual Phase Xe Detector

Dual Phase:

Liquid and Gas Xe

Primary Scintillation in liquid (S1)

Ionization signal from nuclear

recoil too small to be directly

detected => extract charges from

liquid to gas and detect much

larger proportional scintillation

signal (S2)

Time-Projection Chamber:

Z-position of recoil proportional

to drift time

Egas > Edrift

Light Signal

UV ~175 nm

photons

Time

Primary

Proportional

Electron Drift

~2 mm/µs

0–150 µs

depending on

depth

~40 ns width

~1 µs width

S1

Ed

rift

Incoming

Particle

Cathode

e- e- e-

e- e-

S2

Anode

Grid

Eg

as

Scale

Exaggerated

Gas

Liquid


Electron Recoils vs. Nuclear Recoils

Discrimination: Distinctly

different S2 / S1 ratio for

electron / nulcear recoils

Electron Recombination for

Nuclear Recoils is larger

•Light signal (S1) is preserved

• Ionization signal (S2) is

smaller

(S2/S1)NR < (S2/S1)ER

Sensitive

Volume

(15 cm)

Electron Recoil Event

Large S2/S1

Nuclear Recoil Event

Small S2/S1

S1 S2

S1S2

Incoming

Particle

Electron Drift

~2 mm/µs

e-

S1

e- Ed

rift

e-

Cathode

e- e-

S2

Anode

Grid

Eg

as


Dual Phase Xe Detector - Animation


XENON10


The XENON10 Collaboration

Columbia University, Brown University, Case Western Reserve University,

RWTH-Aachen University, Yale University, Rice University,

Lawrence Livermore National Laboratory,

Laboratori Nazionali Gran Sasso (Italy), Universidade de Coimbra


Laboratori Nazionali Gran Sasso (Italy)

3100 m.w.e. → µ flux reduced x10-6 compared to sea level

24 µ / m2 / day


Deployment at Gran Sasso

LdV on site for the commissioning, construction, deployment and operation of detector

Unshielded detector installation March 2006 @ Laboratori NazionaliGran Sasso (LNGS)

Began detector calibration end of March

Shield construction and detector installation: May – August 2006

Calibrations and unblindedbackground data: Sept. – Dec. 1st 2006

WIMP search runs:Oct. 2006 – Feb. 2007

“Unblind” WIMP search data(~ 60 live-days) on April 8, 2007

XENON10 (August 2006)

Detector installation in Shield – Brown group


XENON10 Responsibilities

Simulation of backgroundsConstruction of the XENON10 background model

Shield Design

Advising on design detector

Screening of materials at the SOLO counting facilityHigh-Purity Ge detector at Soudan Mine

DAQ and Trigger design, construction and operation

Involved at all stages of detector construction, calibration and operation

Analysis code development

Data analysisGamma and Neutron calibrations

WIMP search data


Deployment at Gran Sasso


The XENON10 Detector

22 kg of liquid xenon

15 kg active volume

20 cm diameter

15 cm drift

12 kV cathode

Edrift = 0.73 kV/cm

Egas = ~ 9 kV/cm (S2)

Liquid Xe maintained

at T=180 K and P=2.2

atm.

Cooling: Pulse Tube

Refrigerator (PTR),

90W, coupled via cold

finger (LN2 for

emergency)

J. Angle (UFL)

PTR

PMTs

Grids

Teflon

Can

(Active

Volume)


The XENON10 PMTs

89 Hamamatsu R8520-AL

PMTs (1” square)

48 Top + 41 Bottom Array

Quantum efficiency > 20% @

175 nm

~2 x 106 gainx10 amp.


XENON10 - 88 channel DAQ / Trigger System

Designed and constructed by LdV

100MHz Sampling, 14-bit Resolution 160 µs event length x 88 channels

• Sustained ~20 Hz, 45 MByte/sec (WIMP search trigger ~2.6 Hz, 93% live time)

Multi-Event Mode and Dual Memory Bank for Dead-Time Reduction

On-line event compression – baseline suppression

S1 trigger, S2 Trigger and S1+S2 trigger schemes tested – S2 trigger used for all XENON10 results

Struck

VME ADC

100MHz, 14-bit


XENON10 Shield Construction - LNGS

40 Tonne Pb / 3.5 Tonne Poly

20 cm HDPE – 10-2.5 reduction in neutron flux

20 cm Pb – 10-5 reduction in γ flux

3500

mm

2410

mm

Shield design and commissioning by the Brown group

20 cm

HDPE

XENON10

20 cm

Pb


Geant4

model

0

-1

1

XENON10 MC – ER Backgrounds

Gamma Background rates for XENON10 from Monte Carlo models

Use of xyz cuts (Single Scatters in 5.4 kg Fiducial Volume) instead of LXe Outer Veto

Main contribution: Stainless Steel Cryostat

PMT radioactivities (238U / 232Th / 40K / 60Co) obtained from screening 70% of PMTs

Energy [keVee]

10 100 1000

DR

U

10

1

0.1

XENON10 data

Geant4

MC

Steel Cryostat

137Cs from Cryostat walls

85KrPb shieldPMTs

radius [cm]0 2 4 6 8 10

Dep

th [

cm]

0

-5

-10

-15

log

10D

RU

0.01 137Cs from PMTs


XENON10 MC – NR Backgrounds

Main Neutron Backgrounds

PMT (α,N) / Fission subdominant

(α,N) / Fission Neutrons from Rock

Muon Induced Neutrons from Pb

Shielding

Monte Carlo event rates for

neutrons are x1/3 below

XENON10 background goal.

0.3 Nuclear Recoil events expected

in XENON10 WIMP search run (59

days, 5.4 kg fiducial mass)

Low Energy Neutrons are

moderated by 20cm poly inside Pb

shield

Active Muon Shield Not Required

(α,N) Neutron Flux: ~2 x 10-6 n s-1 cm-2

Neutron Yield in Pb: 4 x 10-3 n/(μ g cm-2)


The XENON10 Signal

Primary Scintillation (S1) created by interaction in Lxe Std Pattern - spread evenly

20/80 top/bottom

Secondary Scintillation (S2) following Ionization: e- are extracted and accelerated in Xegas S2 signal Localized in XY - event

position reconstructed from S2 Hit Pattern(σXY ≈ 1 mm)

Z-position proportional to drift time S2_time – S1_time (σZ≈0.3 mm)

Maximum Drift Length= 15 cm / 80 usec

Single Scatters, Fiducial Volume (5.4 kg) Cuts

E=1kV/cm

S2e-e-

e-S1e-e-

e-

e-

e-

S2S1

Incident

Particle

e-

γ 4.5 keVeeVery clean signal !


Discrimination

Neutronsg

Δ log10 ( S2 / S1 )

Gamma Calibration (137Cs)

Neutron Calibration (AmBe)

“Gaussian” Background

Discrimination improves at low energies !

S1 [keVee] (2.2 p.e. / keVee)

0.73 kV / cm

S1 [keVee] (2.2 p.e. / keVee)

2-12 keVee → 99.6%

Δlo

g10

(S2/

S1)

Δlo

g10

(S2/

S1)


Scintillation Yield for Nuclear Recoils (1)

Nuclear recoil light yield Leff = sets the energy scale for nuclear recoils

Precise Leff necessary for high confidence on our threshold

Neutron calibration data vs. MC → determines Leff

Good agreement (within 10%) between data and MC with Leff = 0.19Leff = 0.19 → ~ 1 p.e. / keVr

(LEFT) The spectrum of single scatter nuclear recoils from exposure to an AmBe neutron source (black line, with errors), and the spectrum (red line) from a detailed

Monte Carlo of the experiment, obtained from the best-fit Leff curve shown at right (red line). The result of assuming a constant Leff=0.19 is also shown in blue.

(RIGHT) Schematic of the setup for conventional neutron calibrations, and for the XENON10 neutron calibration

.].p[111

]keVr[ eSLS

S

LE

yn

e

eff

nr

E-field quenching factors

for ER and NR

Data

MC (Leff = 0.19)

trigger

roll-off

Light Yield for 122keVee γ

Neutron Source

XeConventional

Neutron

Calibration

Neutron Source

(AmBe)

Xe

XENON10Pb

(5cm)



Nuclear recoil light yield Leff = sets the energy scale for nuclear recoils

Precise Leff necessary for high confidence on our threshold

Neutron calibration data vs. MC → determines Leff

New best fit Leff curve from maximum likelihood comparison between Monte Carlo and AmBe neutron calibration data Results rule out sharp drop in Leff at low energy

(LEFT) The spectrum of single scatter nuclear recoils from exposure to an AmBe neutron source (black line, with errors), and the spectrum (red line) from a detailed

Monte Carlo of the experiment, obtained from the best-fit Leff curve shown at right (red line). The result of assuming a constant Leff=0.19 is also shown in blue.

(RIGHT) The best fit Leff curves obtained from a maximum likelihood comparison (red). Also shown are data from [Aprile 2005] (triangles) and [Chepel 2006] (squares).

Data

MC

(best fit Leff)

trigger

roll-off

best fit Leff

.].p[111

]keVr[ eSLS

S

LE

yn

e

eff

nr


for ER and NR


Leff = 0.19

MC (Leff = 0.19)


XENON10 WIMP Search Data

XENON10 Blind Analysis – 58.6 days

WIMP “Box” defined at

• ~50% acceptance of Nuclear Recoils (blue

lines):

[Centroid -3σ]

• 2-12keVee

(2.2phe/keVee scale)

23 Events in the Nuclear Recoil

Acceptance Window

13 events are removed from box by

“Gamma-X” Cuts (+)

10 events in the “box” after all primary

cuts (o)

5 of these are not consistent with

Gaussian distribution of ER Background

( WIMPS ? )

log ( S2 / S1) vs S1“Straightened Y Scale” – ER Band Centroid => 2.5

S1

log

( S

2 / S

1 )

“Leakage” Events

Gamma-X cutsNon-Gaussian

Background

ER

NR


“Fake WIMPs” - Gamma-X Events

S1 signals from multiple scatters are indistinguishable – too fast

Scatters in the Reverse Field Region produce S1 light but very little S2 signal – no information for scatters below cathode

Fake WIMPs can occur for Multiple Scatter events with 1 scatter in the Sensitive Volume, 1 scatter in the Reverse Field Region

“Gamma-X”: unknown component for scatters in Reverse Fiducial Region – discrimination not possible

Sensitive

Volume

(15 cm)

Incoming

gamma

Electron Drift

~2 mm/µs

Ed

rift

Cathode

S1

e- e-e-e- e-

S2

Anode

Grid

Eg

as

S1

e- e-e-e- e-

S2

S1 S2 S2

Reverse

Field

Region

(1.2 cm)

Incoming

gamma

Electron Drift

~2 mm/µs

Ed

rift

Cathode

S1

e- e-e-e- e-

S2

Anode

Grid

Eg

as

S1

S1 S2 no S2 !

e-e-

Multiple Scatter Event “Gamma-X” Multiple Scatter Event


“Gamma-X” Event Rate

Geant4 MC of ER background + Gamma-X events

Ratio of Gamma-X events to Electron Recoils ~ 1 / 1000 at 10 keVee

Increases with energy: ~ 1 / 100 at 50 keVee

• Multiple scatters boost S1 signal → few Gamma-X multiple scatters at low

energies

Source:

PMTs + Cryostat

2.2 phe / keVee

~ 1 phe / keVr


Identification of “Gamma-X” events - S1 Hit Pattern

Internal Reflection: Asymmetry of the S1 light – 20% Top / 80% Bottom

Localization of S1 signal for large Z (bottom of detector)

The hit pattern for events at the bottom of the detector tend to be more localized

than events in the bulk, which have a more “spread out” hit pattern

Scatters very close to bottom PMT array (<1cm) tend to deposit most of their light

in a single, or a couple, of PMTs.

Event 2

19.5keVee γ

Z=13cm

Event 1

20.5keVee γ

Z = 8cm

X

Y

Z

still above cathode !

S1 S1


Identifying Anomalous Topologies

Localization of Secondary Scatters (with no associated S2) point to

specific anomalies Reverse Field Region – Secondary Scatters Below Cathode have no Z information, but

exhibit large degree of localization in single PMT and random XY distribution

Gamma-X Events

S1 Hit Pattern

S1 = 18 p.e.

40 µs = 7.5 cm


Applying the Gamma-X Cuts to XENON10 Data

log ( S2 / S1) vs S1“Straightened Y Scale” – ER Band Centroid => 2.5

S1

log

( S

2 / S

1 )

“Leakage” Events

Gamma-X cuts

Glitch

Consistent with Gamma-X

Non-Gaussian

Background

ER

NR

Gamma-X MC slide

XENON10 Blind Analysis – 58.6 days

WIMP “Box” defined at

• ~50% acceptance of Nuclear Recoils (blue

lines): [Centroid -3σ]

• 2-12keVee

(2.2phe/keVee scale)

23 Events in the Nuclear Recoil

Acceptance Window

13 events are removed from box by

Gamma-X Cuts (+)

10 events in the “box” after all primary

cuts (o)

5 of these are not consistent with

Gaussian distribution of ER Background

1 event identified as a glitch (x)

• Coherent noise pick-up

4 remaining event consistent with being

Gamma-X events (x)

• Appear preferentially at higher E

• Clustered at the outer bottom region of

detector, where Gamma-X events are more

likely

• Removed by more advanced Gamma-X cuts

(not applied to the published blind analysis)


Limit Plot

Upper limits on the WIMP-nucleon cross section derived with Yellin Maximal Gap Method (PRD 66, 2002)→No Background Subtraction! Treats all 10 events as possible

WIMP signal

For a WIMP of mass 100 GeV/c2

9.0 ×10-44 cm2 Max Gap

Factor of 2.3 below best previous limit at 100 GeV/c2

(CDMS-II 2004+2005)

Comparable to Zeplin-III (2008) at 100 GeV/c2

XENON10

2007

CDMS-II

2008

Zeplin-III

2008

CDMS-II

2004+2005

Spin-independent

coupling


LUX


The LUX Collaboration

Brown University, Case Western Reserve University,

Lawrence Livermore National Laboratory

Lawrence Berkeley National Laboratory

University of Maryland, Texas A&M, UC Davis

University of Rochester, Yale University


Large Underground Xenon (LUX)

Homestake Mine – Sanford Lab (SUSEL)

Davis Lab at 4850L (~1.5 km deep)

Homestake Mine (South Dakota, US)

4300 m.w.e. → µ flux = 4 µ / m2 / day

reduced x10-7 compared to sea level

Davis Cavern

Water Shield

LUX

Thermosyphon


Sanford Lab at Homestake Mine

Sanford Lab at the Homestake Mine (South Dakota, US)

LUX will be deployed in the Davis Cavern at 4850 feet level (~1.5 km deep)

LUX Collaboration Meeting at Homestake, March 2009


The LUX Detector

350kg Liquid Xe Detector (59cm height, 49cm diameter)

120 Hamamatsu R8778 PMTs (2” round): 60 on top, 60 on bottom

Low-background Ti Cryostat

Thermosyphon: >1 kW cooling power

Titanium Cryostat PMTs

(60 Top / 60 Bottom)

Teflon Can

R8778 PMTs


LUX Water Shield

Water Tank: d = 8 m, h = 6 m

(300 Tonnes)

3.5m shield thickness on the sides

Inverted steel pyramid (20 tons) under tank to

increase shielding on top/bottom

Ultra-low background facility

Geant4 MC of LUX backgrounds

Gamma event rate reduction: 2 x 10-10

High-Energy Neutrons (> 10 MeV) flux

reduction ~ 10-3

Inverted Steel pyramid

2.75 m

1.2 m

3.5 m

Water

Shield

(300T)

Flu

x R

edu

ctio

n

Rock Neutrons

(<10 MeV)

µ-induced Neutrons

(>10 MeV)

Gammas

Flux Attenuation in Water

(Geant4 MC)

0 1 2 3 4

Shield Thickness (m)


LUX Background Studies - Gammas

Background Model for LUX detector – Monte Carlo

simulations using Geant4

Gamma Backgrounds

MC determined shape of detector (tall, not “pancake”)

All detector components are being screened for

radioactivity at the SOLO and LNGS counting

facilities

External sources contribution < 10-4 than PMT

contribution

85Kr reduced to <2ppt ( < x1/2 of PMT background)

Dominated by PMTs: 390 µdruee

(PMT radioactivity for 238U / 232Th / 40K / 60Co measured

at SOLO)

1 event in 45,000 kg-days at 99.4% discrimination

Gamma-X backgrounds:

Ratio: 500:1 Gamma to Gamma-X events in 0-30keVee

Equivalent to 99.8% discrimination > 99.4%

discrimination goal for LUX

Rate further reduced by applying Hit Pattern cuts

(same as developed for XENON10)

Gammas from PMTs

optimal fiducial mass = 100kg

390 udrur

Rat

io G

amm

a-X

/ G

amm

a ev

ents

1e-1

1e-2

1e-3

Gamma-X Events

All events

Fiducial volume events (100kg)

Source: PMT gammas


LUX Background Studies - Neutrons

Background Model for LUX detector – Monte

Carlo simulations using Geant4

Neutron Backgrounds

External: High Energy µ-induced neutrons from

rock and water tank < 200 ndrur

(before Muon veto)

Internal: (α,n) neutrons from PMTs ~ 500 ndrur

(conservative estimate for 5 N / year / PMT)

• 238U / 232Th alpha decays

• Muon veto can also veto neutron events,

which are likely to scatter once in the

detector and then in the water

~66% capture efficiency

Achieve 1 NR event in 1,000 days with fiducial

volume of 100 kg (5-25keVr)

Neutrons from PMTs

500 ndrur

optimal fiducial mass = 100kg

All Events

Single Scatters

Veto neutron

capture in water

(x3 reduction)


LUX Projected Goal

Spin-independent

coupling100 GeV WIMP → 7 x 10-46 cm2

(XENON10: 8.8 x 10-44 cm2 for 100 GeV WIMP)

LUX

CDMS-II

XENON10

ZEPLIN-III (2008)

ZEPLIN-III (after PMT updates)

XMASS (2009)

SuperCDMS

SNOLab (2013)

LUX

x20 bigger

x100 better

sensitivity


Simulated signal in LUX

300 days acquisition, 100 kg fiducial mass

ER Background ~390 µdru

Leff = 0.19

Using same

ER and NR bands

as XENON10

ER

NR

NR band mean

NR band -3σ

γ background


Simulated WIMP signal in LUX

300 days acquisition, 100 kg fiducial mass

ER Background ~390 µdru

What will WIMPs look like in LUX?

Example: mWIMP = 100 GeV/c2 and σWIMP = 2.1x10-45 cm2 (3x the estimated LUX sensitivity)

Leff = 0.19

Using same

ER and NR bands

as XENON10

ER

NR

NR band mean

NR band -3σ

ER background

WIMPs


LUX 0.1

4 PMT initial run of the LUX detectorDetector is filled with 50kg of Liquid Xe

+ ~260kg Aluminum can (to be replaced with 350kg of Liquid Xe in LUX 1.0 run)

2” active Xe region

Currently under operation at Case Western University (OH), and is being used to test all LUX subsystems

LUX 0.1 PMT Assembly LUX 1.0 PMT Assembly


LUX 0.1 Installation

Detector built and assembled at Case – Spring 2008

260kg of Al

(to be replaced

by 350kg of LXe)LUX 0.1

Steel

Cryostat

(to be

replaced

with Ti)


LUX 0.1 - Milestones

Detector built and operational at Case

Detector filled with 50kg of Liquid Xe

S1 and S2 pulses observed

Subsystems tested and deployed at Case:

Thermosyphon Cooling System

• Rapid (high power: >1kW) cooling system

Recirculation System

• It will permit 50 slpm of LXe

High Voltage Feedthroughs

Slow Control and Safety Systems

Data Acquisition System

• Pulse-Only Digitization mode successfully

tested

Custom built amplifiers and trigger system

• Digital Trigger with S1/S2 recognition,

based on DDC-8 acquisition boards


LUX 0.1 – Brown at Case

Brown presence at Case since

March 2008Assembly and deployment of detector

Operations – running the detector

Development of Safety Protocols and

Testing of Safety Systems

Brown responsible for electronics

subsystems and analysis software

in LUX0.1Data Analysis Software

DAQ System• Pulse Only Detection (POD) mode

LED Calibration System

PMTs


Larger Detectors

Monte Carlo of larger detector masses

Evolution of fiducial volume: more mass → more self-shielding

Larger fraction of low-background volume available

LUX (350 kg) = 33% fiducial volume

20T

= 66% fiducial

volume

detector rate / mass = constant

LUX

350 kg

3T

10T 20T


LZ20

LZ20

LZ3

LUX

CDMS-II

XENON10

ZEPLIN-III (2008) ZEPLIN-III

LUX-Zeplin Collaboration: 20 Tonnes liquid Xe detector

Estimated Schedule for Construction and Operation: 2012 and 2015

LZ20 Baseline Design


Conclusions

XENON10 Liquid Xe detectors work, and well

Has delivered very competitive results

Gamma-X backgrounds, although <1% effect, could become a problem if not accounted for in larger detector design

LUX builds on established Xe technology

Self-shielding = efficient background reduction

Dominant background is from PMTs

• Screening show lower radioactivity (x1/3 ) than original estimates

BG model predicts 1 ER and 1 NR event in energy window, for 100 kg and 1000 days

Expect sensitivity to (100 GeV) WIMP dark matter of 7x10-46 cm2

• x100 times below current limits

First stage of LUX detector is already running

LUX deployment at the Homestake Mine - Summer 2009

LUX Underground operation by the end of 2009

De Viveiros

The End

Thank You

De Viveiros

Extra Slides


XENON10 Material Screening

• Dedicated Low Background Facility at Soudan: SOLO (operated by Brown)

• High Purity Ge detector:”Diode-M” 0.6 kg (Brown) and “Gator” 2 kg (UFL)

• Also use LNGS screening Facility (Laubenstein, LNGS)

• Screening of PMTs, electronic components, construction materials

• Currently screening materials for the LUX experiment

Diode-MDiode-M

40K

1460 keV

Pb X-rays10

1

0.1

Diode-M Background

DRU

Energy [keV]1 DRU = 1 event / keV / kg / day


XENON10 Trigger Threshold

S2 Trigger:

Σ(34 top-center PMTs)

Integrate with τ = 1 μs

Threshold discriminator

S2 trigger efficiency >99%

at 4.5 keVr (= 2 keVee)

Typical S2:

ER (2 keVee): 2800 phe (~100 e-)

NR(4.5 keVr): 1100 phe (~40 e-)

Smallest NR S2 at 4.5keVr

threshold: 300 phe (~12 e-)

S2 Histogram (AmBe Data)

Analysis Software

Threshold (S1 n ≥ 2)


Scintillation

XENON10 primary scintillation (S1) light yield in terms of PMT photo-

electrons per keVee (Nphe/keVee)



Independent Verification through the Ionization Yield, calculated with the Multiplicity MethodRatio of 1 / 2 / 3 scatters dependent on the threshold for

individual scatters

Compare Data (# of p.e.) to MC (keVr)

24±7 p.e. / e-

.].p[111

]keVr[ eSLS

S

LE

yn

e

eff

nr


for ER and NR



XENON10 WIMP Search Run

WIMP search run: 59 live-days,

blinded

~20 days of WIMP search data

unblinded to test and optimize

calibrations and cuts

not blind

background

blinded

WIMP

search

high stats

γ-calibration

neutron

calibration

(see next slide for flagged events)


LUX DAQ – Design and Upgrade

•122 channels based on 14 bit VME Struck ADCs - 10 ns/sample, 700 µs event length

Pulse-Only Digitization (POD) mode Software Developed by Brown and Struck to increase data throughput

Struck ADC Boards (same as XENON10) => Firmware Upgrade

Data is acquired only when below a given threshold

• Decreases the amount of data that needs to be transferred through the VME bus

• Saves Hard Disk Space

Maximum Acquisition Rate for “Classic” DAQ: 5Hz

• 60cm Drift Length requires ~ 17 MB per event (122PMTs)

Maximum Acquisition Rate for P.O.D. DAQ: 1300 Hz

• (P.O.D. rate allows for 500Hz spurious pulses per channel)

P.O.D. Mode

Baseline not acquired

ch 1

ch 2

ch 3

ch 4 LUX0.1 Sample Event

S1

200 p.e.

S2

5000 p.e.

0

-100

-200

-300

-400

-500

-600

-1 0 1 2 3 4 4 5 6

mV

µs

Searching for Dark Matter From XENON10 to LUXlux.brown.edu/talks/20090330_ldv_coimbratalk_v8.pdfDe...

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