t. shutt- the xenon dark matter search

8/3/2019 T. Shutt- The XENON dark matter search

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The XENON

dark matter search

T. Shutt

CWRU


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T. Shutt 8/16/05 2

The XENON collboration

Columbia UniversityElena Aprile (PI), Edward Baltz ,Karl-Ludwig Giboni, Sharmila Kamat,

Pawel Majewski ,Kaixuan Ni, Bhartendu Singh, and Masaki YamashitaRice University

Uwe Oberlack ,Omar VargasCase Western Reserve University

Alex Bolozdynya, Eric Dahl, Jennifer Kalb, John Kwong, Tom Shutt,Matt Whilden

Brown University

Richard Gaitskell, Peter Sorensen, Luiz DeViveirosLawrence Livermore National Laboratory

Adam Bernstein, Chris Hagmann and Celeste Winant

University of FloridaL. Baudis, J. Orboek, A. ManalaysayYale University

D. McKinsey, R. Hasty, A. Mazur


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CDMSII

Edelweiss

Current limits

~ 0.1 cnts/

kg/day


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How big?

Motivation for very large detector clear

"Generic" test of MSSM possible with 1-10 tons

Less restrictive framework can allow lower rates

If signal seen, need larger mass to probe modulation.

Current limits: 0.2 event/kg/day

Ellis, Olive, Santoso,Spanos, hep-ph/ 030875

Calculations in minimal supersymmetry framework (MSSM).


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Promise of liquid Xenon. Good WIMP target.

Readily purified

Self-shielding - high density, high Z.

Can separate spin, no spin isotopes129Xe, 130Xe, 131Xe, 132Xe, 134Xe, 136Xe

Rich detection media

Scintillation

Ionization

Scalable to large mass


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Basic processes in liquid Xenon Complicated atomic processes

Scintillation - 175 nm Singlet ( 3 ns), triplet ( 27 ns)

Ionization Recombination (15 ns)

Energy per quanta (electron recoils):

charge: 20 eV

Photon: 20 eV

Difference between e and n recoils

Nuclear recoils, electronic excitations suppressed by 5.

Nuclear recoils suffer recombination

dE

dxv

2


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LXe

PMTs

A. Bolozdynya, NIMA 422 p314 (1999).

WIMP

Dual Phase, LXe TPC

5s/cm

~1 s

---

-

Ed

Es

Time

Time

~40 ns

Very good event location. Good discrimination despite

small number of e-,

Need single charge, photon

sensitivity

Use charge amplification insteadof increasing E/kT.

Competitors: ZEPPLIN II, III

ITEP

XMASS_DM

Ar detectors (Icarus, FLARE)

Charge drift easier.

39Ar background.


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Discrimination of nuclear recoils Electron recoils - background. Gammas, X-rays, betas.

Nuclear recoils - signal: High density track. Charge recombination. Possible changes inscintillation time profile.

Suppression (Lindhard) of both charge and scintillation.

light

Background:

electron recoils

Signal: nuclear recoils

charge

light

Recombination fornuclear recoils

discrimination

Ionization

Scin

tillation

Effect of recombination

(122 keV gammas)Recombinat

ion


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Detectors

2004 - 1 kg LXe

Currently - 3 kg LXe


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Neutron beam calibration of scintillation

Liquid

scintillator

neutron

beam

Liquid Xe

Er= E

n

4mM

m + M

1

2(1+ cos)

Columbia/Yale


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Measured by two groups,detectors. Case

Columbia/Brown

Detectors: 4 cm , 1 & 2cm deep.

Full measurement of nuclear recoils

Charge calibrated directly with 122keV gammas and alphas.

Energy relies on previous n-beamcalibrations.

Note: Columbia geometry has x 5light collection over Case.

PMT in liquid instead of gas.

40keV gamma

(inelastic n-Xe)

206Pb-recoils

Xe recoils from

neutrons

Case

Columbia/Brown


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Preliminary look at discrimination

gammasn-recoils

Neutrons Gamma Background

Limitations: Light collection statistics

With current data, rejection robust ~ 20keV.

Poor charge collection

At edges (only?) Rejection > 104 for alphas in center of

detector.

Currently 98 % at high energies.

Basic processes compatible with very highdiscrimination for E > ~20 keV.


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Ionization yield

Larger than expected based on alphas. Easy to measure!

Not as distinct from gammas as expected.

Physics: dq/dx(E,E) (from dE/dx) + recombination

Surprising field independence

Increase at low energy agrees with dE/dx.

Versus energy Versus electric field

Electr

ons/keVnre


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Quenching Factors vs Drift Field

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1000 2000 3000 4000 5000

Drift Field (V/cm)

Quenchingfactors,normalizedto

full(no)recombinatio

nforlight(charge))

Alpha Charge (Po210)

Gamma Charge (Co57)

Alpha Light (Po210)

Gamma Light (Co57)

LXe processes

New measurement of 122 keV gammas (57Co).

Agreement between single phase and dual phase data.


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Single electrons and photons

Threshold and stability quite important. Electric fields present challenge: 5 kV/cm -

liquid; 12 kV/cm gas.

With single-PMT system, havedemonstrated stable triggering over

2months.

Single photo-

electron threshold

S2: ~ 1.5 electrons

S1: ~ 5 keVnr

Light: < 1 p.e. Issue is light collection.

Charge threshold ~ 1 electron.


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Scintillation peak ~175 nm (VUV).

Total internal reflection n ~ 1.6, 40% transmission (2).

Collection at bottom ~ 5 times better than collection above.

Light collection

Current technology: PMTs in liquid and gas

Hamamatsu 5820, 1 square, 17 % effective QE.

~ 1 p.e./keV for nuclear recoils.

Alternative: CsI photocathode.

PMTs top and bottom, PTFE walls, 4 grids

Top PMT Bottom PMT


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Capacitance level sensor Liquid level critical

With 2, determines field that gives

charge signal.

Sensors: parallel plates capacitors

~ 1-2 pF empty-full

Cx

Zf

Vi ViV

o

=

Z

Zx

Virtual ground readout

f F sensitivity

Independent of stray capacitance.

4 mm


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MC: gamma Background from PMTs

Inner PMTs - Hamamatsu 8778(232Th/238U/40K/60Co):

XENON10 Target

XENON100 Target

PMTs


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Hamamatsu PMTs

34 60

53 0

13

15

310 12010

1090504

0360

Th

Series60Co

U

Series40K

Designed for XMASS.

Coverage Area: 49.7%

Columbia tested at 150K/4

atm

80 mBq(expect further improvement)

5 cm x 12

cm

QE 26%R8778

Square/quad anode-good

fill factor (66.2%).Columbia tested at

150K/4 atm23 mBq

(2.5

cm)2x3.5cm

QE >20%R8520

Evolution of 6041143 mBq

(Use of Kovar for most of base)

5 cm x 4

cm

QE 20%R9288

Specifically designed for

ops in LiqXe TPC

5500 mBq(Dominated by glass seal at base)

5 cm x 4

cm

QE 5-8%

R6041

Comment

Radioactive Background

[mBq/tube]Dimension& QE

PhotoModel


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Gamma/Electron Background MC

(removed by Gas sep./getter)Tritium

9Polyethylene Shield

< 5External/Pb shield Gammas

< 1Teflon Walls

~< 40 mdruTotal

< 5210Pb Brem (Pb shield 30

Bq/kg)

< 685Kr (< 0.1 ppb)

12Stainless Steel Cryostat

1.6HV Shaping Ring Resistors

0.6416 Outer PMTs

9 (5 *)7 Inner PMTs

Rate [ mdruee ]Source

Goal for XENON10, 8 < E < 16keVee: 0.140 cnts/kg/keV/day

before 99.5 % rejection. Assumes using 5 cm outer LXe active veto and inner multiple scatters cut

mdruee = 10-3 evts/keVee/kg/day* if a 1 cm depth cut is made at top of inner LXe


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XENON10 Neutron Background MC

6 *Muon-Induced Neutrons from Poly

Shield

0.01PMT/Stainless Internal (,n) Neutrons

15(,n)/Fission Neutrons from Cavern

10 *Muon-Induced Neutrons from Pb Shield

3 **High Energy Muon-Induced Neutrons

from Rock

34 drurTotal

Inner Event Rate (no cuts)

(@ 2 keVr) [ drur ]Source

Neutron Background Event Rates for XENON10 Module

XENON10 Goal is 1.3 evts/10kg/month =>360 drur (100GeVWIMP)

Assumes LNGS 24 /m2/day (No muon veto required)

drur = 10-6 evts/keVr/kg/day* factor 2 uncertainty

** factor 4 uncertainty


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Kr removal 85Kr (, 687 keV endpoint).

Best commercial Xe: 5 ppbKr/Xe (XMASS)

Goals: XENON10 (100,1000)

< ppb, (100, 10 ppt)

Possible separation methods:

Distillation - (XMASS)

Chromatography.

Kr

Xe

KrXe

charcoal column

Projected performance, 1 Kg

charcoal column:

1.8 Kg Xe/day

Purification 103

Use 14 stp m3 He/ Kg Xe

processed.

High purity system being

commissioned.


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Xe purity - chemical Xe is not so noble.

high polarizability (same as alkanes)

e- attachment during drift

SF6

O2

N2O

Mitigation:

Detector cleanliness, bakeout. Commercial high temp., Zr-based getters

Recirculation in gas phase

Demonstrated: > 1 m drift length.

~ 2 month stability.

1 cm

~ 40 cm

TPC measurement


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XENON10 program Basic R&D demonstrated:

Discrimination of nuclear recoils

at low energy. 1 kg, 7 PMT detector.

> 1 m charge drift.

Stable cryogenics.

3 kg, 21 PMT detector now underoperation.

This fall -> 10 kg detector.PMTs top + bottom.

10 kg detector in Gran Sasso in2006

Field shaping

21 PMT array

(top and bottom)

diving

bell


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Gran Sasso Installation

First installation - modest size. Power: 20 kW, (15 kW UPS)

LN2 (440 liters/week)

100 kg installation will not be

much larger.


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Projected sensitivity

CDMSIIgoa

l

XENON10

XENON100

Edelweiss

XENON1T

CDMSII


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For a large-scale experiment

Purification in liquid phase - sparkpurifier

CsI photocathode


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CsI photocathode

Gate

Transmission

Anode

CsIphotocathode

Edrift

E1

E1E

0

E1

Gated

Edrift

PMT PMT

Positive feedback: gating required.

CsI photocathode good match to thisapplication

VUV sensitive, "robust

CsI radioactivity negligible for < mphotocathode.

Commercial:V ~ 10 kV in < 1 s.

Preliminary tests encouraging.

S1

S1

S2

S3

S4


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For a large-scale experiment

Purification in liquid phase - sparkpurifier

CsI photocathode

Charge-gain readout

High quality x-y reconstruction.Especially lack of tails.

Radioactivity

Cost Gas gain of > 1000 needed.

Measured gain, 175 K.


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t. shutt- the xenon dark matter search

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