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Light Detection in XENON100 and Small-Scale LXe R&D

Detectors

Guillaume Plante

Columbia University

on behalf of the XENON Collaboration

LIDINE2013 - FNAL - May 31, 2013

Outline

Guillaume Plante - XENON LIDINE2013 - May 31, 2013 2 / 28

• XENON100

• Design

• PMT Arrays

• Light Detection Performance

• Status

• R&D Detectors

• XeCube2

• neriX

XENON100

XENON Program


XENON10 XENON100 XENON1T

2005-2007 2008-2013 2013-2017

Achieved (2007) Achieved (2011) Projected (2017)σSI = 8.8× 10−44 cm2 σSI = 7.0× 10−45 cm2 σSI ∼ ×10−47 cm2

Achieved (2012)σSI = 2.0× 10−45 cm2

XENON100 Collaboration


Columbia Rice UCLA Zurich Coimbra LNGS Mainz SJTU Bern

Bologna MPIK NIKHEF Purdue Subatech Munster WIS

Why Xenon?


• Large mass number A (∼131), ex-pect high rate for SI interactions(σ ∼ A2) if energy threshold for nu-clear recoils is low

• ∼50% odd isotopes (129Xe, 131Xe)for SD interactions

• No long-lived radioisotopes (with theexception of 136Xe, T1/2 = 2.1 ×

1021 yr), Kr can be reduced to pptlevels

• High stopping power (Z = 54,ρ = 3g cm−3), active volume is selfshielding

• Efficient scintillator (∼80% lightyield of NaI), fast response

• Scalable to large target masses

• Nuclear recoil discrimination with si-multaneous measurement of scintilla-tion and ionization

10−5

10−4

10−3

Tot

alR

ate

[evt/

kg/

day

]

0 10 20 30 40 50

Eth - Nuclear Recoil Energy [keV]

Si (A = 28)

Ar (A = 40)

Ge (A = 73)

Xe (A = 131)

σχN = 1 × 10−44 cm2

Principle


Eionization

excitation

Xe++ e−

+Xe

Xe+

2

+e−

Xe∗∗+XeXe∗

+Xe

Xe∗2

2Xe

178 nmsinglet (3 ns)

2Xe

178 nmtriplet (27 ns)

• Bottom PMT array below cathode, fully immersed in LXeto efficiently detect scintillation signal (S1).

• Top PMTs in GXe to detect the proportional signal (S2).

• Distribution of the S2 signal on top PMTs gives xy coordi-nates (∆r < 3mm) while drift time measurement providesz coordinate (∆z < 300µm) of the event.

• Ratio of ionization and scintillation (S2/S1) allows discrim-ination between electron and nuclear recoils.

XENON100: Design


PMT HV and Signal Lines ❛❛❛❛❛❛❛❛❛❛❛❛

❆❆❆❆Anode Feedthrough ❝

❝❝❝❝❝❝❝❝❝❝

Tube to

Cooling

Tower

Top Veto

PMTs

Top Array

PMTs✭✭✭✭✭✭

PTFE

Panels✭✭✭✭✭✭✭✭✭

Side Veto

PTFE Lining✱✱✱

Lower Side

Veto PMTs✏✏✏✏✏

Bottom Array PMTs ✑✑✑✑✑✑✑✑✑✑✑✑

Double-Wall

Cryostat

✔✔

✔✔

✔✔

✔✔

✔✔

✔✔

✔✔

✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄

Upper Side

Veto PMTs��

��

Bell✭✭✭✭✭✭✭✭

Top Mesh✘✘✘✘✘✘✘✘Anode

Bottom Mesh❳❳❳❳❳❳❳

Field

Shaping

Rings

✭✭✭✭✭✭✭✭

Cathode❤❤❤❤❤❤❤❤❤

Bottom Veto PMTs

❧❧

❧❧

❧❧

• Goal was to build a detector with a ×10 increase infiducial mass and a ×100 reduction in backgroundcompared to XENON10.

• All detector materials and components werescreened in a dedicated low-background countingfacility

• 161 kg LXe total mass consisting of a 62 kg targetsurrounded by a 99 kg active veto. 15 cm radius,30 cm drift length active volume.

• TPC inner volume defined by 24 interlocking PTFEpanels. Drift field uniformity ensured by 40 doublefield shaping wires, inside and outside the panels.

• Cathode at -16 kV, drift field of 0.533 kV/cm. An-ode at 4.4 kV, proportional scintillation region withfield ∼12 kV/cm. Custom-made low radioactivityHV feedthroughs.

• Aprile et al., Astropart. Phys. 35, 573, 2012

XENON100: PMT Arrays


• 242 low activity Hamamatsu R8520-06-Al 1” squarePMTs,

• 98 tubes on top (QE ∼23%), in concentric circles andenclosed in a PTFE structure,

• 80 high QE (∼33%) tubes on bottom, on a rectangu-lar grid to maximize photocathode coverage,

• 64 tubes in the LXe veto, in two rings, alternatinginward and down (up) to allow them to view the top,bottom and sides of the veto volume.

XENON100: Typical Low Energy Event


s]µDrift Time [0 20 40 60 80 100 120 140 160 180

Am

plitu

de [V

]

0.0

0.5

1.0

1.5

Veto

Am

plitu

de [V

]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

TPC

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

0.00

0.05

0.10

0.15S1: 14.1 pe

170 171 172 173 174 175 176 177

0.0

0.1

0.2

0.3 S2: 926.1 pe

XENON100: Typical Low Energy Event


1

2

3

4

5

67

8 910

11

12

13

14

15

16

17

18

19

20

2122232425

26

27

28

29

30

31

32

33

34

3536 37 38

39

40

41

42

43

44

45

46

47484950

51

52

53

54

55

56

57

5859 60 61

62

63

64

65

66

67

68697071

72

73

74

75

76

7778 79

80

81

82

83

848586

87

88

89

9091

92

93

9495

96

97 98179

180

181

182

183

184

185186 187 188

189

190

191

192

193

194

195

196

197

198

199

200

201202203204

205

206

207

208

209

210

99 100 101 102

103 104 105 106 107 108 109

110 111 112 113 114 115 116 117 118

119 120 121 122 123 124 125 126 127 128

129 130 131 132 133 134 135 136 137 138

139 140 141 142 143 144 145 146 147 148

149 150 151 152 153 154 155 156 157 158

159 160 161 162 163 164 165 166 167

168 169 170 171 172 173 174

175 176 177 178

211

212

213

214

215

216

217218 219 220

221

222

223

224

225

226

227

228

229

230

231

232

233234235236

237

238

239

240

241

242

[pe]

PM

Ti

S2

0

20

40

60

80

100

120

140

XENON100: Position Dependent Corrections


Z [mm]

-300-250

-200-150

-100-50

0Radius [mm]

0 20 40 60 80 100 120 140

rela

tive

LCE

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

histEntries 2888Mean x -178.9

Mean y 72.85

RMS x 86.59

RMS y 43.28

histEntries 2888Mean x -178.9

Mean y 72.85

RMS x 86.59

RMS y 43.28

x [mm]-150 -100 -50 0 50 100 150

y [m

m]

-150

-100

-50

0

50

100

150

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

• Corrections from measurements with 137Cs,AmBe (40 keV inelastic), 131mXe (164 keV),with agreement better than 3%.

• S1 rz and S2 xy correction due to spatial de-pendence of the light collection.

• S2 z correction due to finite electron lifetime.

XENON100: Light Yield and Energy Resolution


Energy [keVee]10 210 310

Ligh

t Yie

ld [P

E/k

eVee

]

1.5

2

2.5

3

3.5

Kr83m

Kr83m

Xe139Xe131

Xe131m

Cs137Co60

XENON100 Measurements

XENON100: Interpolation at 122 keVee

Manalaysay et al. (2010)

Energy [keVee]0 200 400 600 800 1000 1200 1400

/E)

[%]

σR

esol

utio

n (

0

2

4

6

8

10

12

14

16

18

20S1 signal

S2 signal

Combined S1, S2

• Volume averaged light yield at 0.530 kV/cm measured with several γ sources

• Limited penetration depth of 122 keV γ rays into the sensitive volume makes an in-situcalibration impossible

• Light yield at 122 keV is interpolated using the NEST LXe scintillation model

XENON100: Limit


]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000

]2W

IMP

-Nuc

leon

Cro

ss S

ectio

n [c

m

-4510

-4410

-4310

-4210

-4110

-4010

-3910

]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000

]2W

IMP

-Nuc

leon

Cro

ss S

ectio

n [c

m

-4510

-4410

-4310

-4210

-4110

-4010

-3910

]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000

]2W

IMP

-Nuc

leon

Cro

ss S

ectio

n [c

m

-4510

-4410

-4310

-4210

-4110

-4010

-3910

DAMA/I

DAMA/Na

CoGeNT

CDMS (2010/11)EDELWEISS (2011/12)

XENON10 (2011)

XENON100 (2011)

COUPP (2012)

SIMPLE (2012)

ZEPLIN-III (2012)

CRESST-II (2012)

XENON100 (2012)observed limit (90% CL)

Expected limit of this run:

expectedσ 2 ± expectedσ 1 ±

• Strongest limit to date over a large WIMP mass range, continues to challenge the interpretationof DAMA, CoGeNT, and CRESST-II signals as being due to scalar WIMP-nucleon interactions

• Aprile et al., Phys. Rev. Lett. 109, 181301, 2012

XENON100: Status


• Several analyses underway with data alreadyin hand

• Electronic recoil background rate stabilityanalysis

• Detector response to single electrons

• Ultra-low S2 (few electrons) analyses

• . . .

• Continue operation and taking data with lowbackground

• AmBe calibration just finished

• XENON1T begins construction this summer!

XENON1T

Small Scale R&D Detectors

XeCube2: LXe Detector: Design


• Built a special purpose LXe detector withmaximized scintillation light detection ef-ficiency

• LXe detector used to measure Leff downto 3 keV (PRC 84, 045805 (2011))

• Cubic sensitive volume with six 2.5 x 2.5 cmHamamatsu R8520-406 SEL High QE PMTs

• Calibration with 122 keV γ rays from a 57Cosource gives a light yield of Ly = 24.14 ±

0.09(stat)±0.44(sys) pe/keVee with a resolution(σ/E) of 5%

• Very high light yield, enables a measurement witha low energy threshold

Measurement of Leff : Setup


LXe

d

2H(d, n)3Heϕ = π

2

EJ301

EJ301

n

θ

θ

• Record fixed-angle elastic scatters of monoenergeticneutrons tagged by organic liquid scintillators withn/γ discrimination

• Use 2H(d, n)3He 2.5 MeV neutrons from a compactsealed-tube neutron generator

• Recoil energy is fixed by kinematics

Er ≈ 2EnmnMXe

(mn +MXe)2(1− cos θ)

Time of Flight [ns]-50 0 50 100 150

]-1

d-1

Rat

e [e

vent

s ns

0

50

100

150

200

250

300

n

γ o = 34.5θ 1.0 keV±6.5

Accidentals Accidentals

Scintillation Signal [pe]0 10 20 30 40 50 60 70

]-1

d-1

Rat

e [e

vent

s pe

0

20

40

60

80

100o = 34.5θ

1.0 keV±6.5

Measurement of Leff : Result


Nuclear Recoil Energy [keV]1 10 100

eff

L

0.00

0.05

0.10

0.15

0.20

0.25

0.30Sorensen 2009Lebedenko 2009Horn 2011 (FSR)Horn 2011 (SSR)Aprile 2005Aprile 2009Chepel 2006

Manzur 2010Plante 2011

• Lowest energy (3 keV) and most precise Leff direct measurement achieved to date.

• For details see Plante et al., Phys. Rev. C 84, 045805, 2011

Measurement of Re: Setup


• Ideally, what we would like to have is a way to gen-erate electronic recoils of a fixed energy homoge-nously inside the LXe volume, then “simply” mea-sure the response

• The Compton coincidence technique (Rooney andValentine, IEEE Trans. Nucl. Sci., 43, 1271, 1996)allows essentially that

• The energy of the recoiling electron is given

Eer = Eγ − E′

γ

Eer = Eγ −Eγ

1 +Eγ

mec2(1− cos θ)

• Measure the energy of scattered γ rays and use theexcellent energy resolution of the HPGe detector toselect events with nearly monoenergetic electronicrecoil energies in the LXe detector.

• LXe detector should have a high light detection ef-ficiency to achieve a low energy threshold

• Energy resolution of the far detector determines theminimum spread in selected recoil energies in theLXe detector

LXe

detector

PMTs

137Cs

HPGedetector

γ

γ′

θ

Measurement of Re: Scintillation Response


Scintillation Signal [pe]0 200 400 600 800 1000 1200

]-1

Rat

e [e

vent

s pe

0200400600800

1000120014001600 o = 8.6HPGeθ

1.0 keV± = 8.2 erE = [653,654] keVHPGeE

[keV

]H

PG

eE

630

640

650

660

Accidental coincidences

Accidental coincidences

Partial energy deposited in HPGe

Full energy deposited in HPGe

Measurement of Re: Result


Electronic Recoil Energy [keV]1 10 210

, Rel

ativ

e S

cint

illat

ion

Yie

lde

R

0.6

0.7

0.8

0.9

1.0

1.1

Energy [keV]

Re

0.5 1 2 5 10 20 50 100 2000

0.2

0.4

0.6

0.8

1

Obodovskii (1994)Aprile (2012)NEST (v0.98, 2013)

Compton scatters (this work)Calibration sources (this work)Band used for threshold calculation

• Data taken at many scattering angles, 0◦, 5.6◦, 8.6◦, 12.0◦, 16.1◦, 21.3◦, 28.1◦, and 34.4◦, tocover electronic recoil energies from ∼2 keV to 125 keV.

• The scintillation yield at different electronic recoil energies is obtained by calculating the LXescintillaton response in a series of slices of scattered γ energies.

• For details see Aprile et al., Phys. Rev. D., 86, 112004 (2012)

talk by A. Manalaysay, arXiv:1303.6891

XeCube2: Light Detection Efficiency


X [mm]-15 -10 -5 0 5 10 15

Y [m

m]

-15

-10

-5

0

5

10

15

Ligh

t Det

ectio

n E

ffici

ency

0.23

0.24

0.25

0.26

0.27

X [mm]-15 -10 -5 0 5 10 15

Y [m

m]

-15

-10

-5

0

5

10

15

Ligh

t Det

ectio

n E

ffici

ency

0.28

0.29

0.30

0.31

0.32

• Is there an explanation for the extremely high lightyield measured at 122 keV?

• One possibility: angular dependence of the PMTresponse, effect much more dramatic with a smalldetector

• Light detection efficiency estimated from MC in-creases significantly if we include this effect

• Unfortunately no measurements for the R8520 at178 nm. . .

Angle of Incidence [rad]-1.5 -1 -0.5 0 0.5 1 1.5

Rel

ativ

e R

espo

nse

0.0

0.2

0.4

0.6

0.8

1.0

1.2

neriX: New LXe Detector


• Dual-phase Liquid Xenon (LXe) Time Projection Chamber (TPC) for measuring nuclear andelectronic recoils in Xe (neriX)

• Designed for simultaneously measure the scintillation and ionization signals from low-energyinteractions in LXe

• Uses of the same cryogenics/gas system infrastructure built for previous measurements atColumbia

• Fully constructed and operational

neriX: Design


• Simultaneous measurement of the scintillationand ionization signals

• 3D position reconstruction

• High light detection efficiency

• Highly configurable design with stackable PTFEpieces

• Reduced amount of materials in the vicinity ofsensitive volume

• Liquid level change measured to 0.05 mm by cus-tom capacitive level meters

neriX: Assembly


neriX: Scintillation and Ionization Yield of ER


• Obtain scintillation and ionization yield as function of recoil energy and drift field

• Data taken at cathode voltages of 0, 1.25, 2.5, 5.0 kV corresponds to drift fields of 0, 0.59, 1.03,1.90 kV/cm

• Future measurements will go down to ∼1 keV with ∼1 keV bins at the lowest energy

• Initial trial measurement helped optimizing many parameters: PMT gain, linearity, trigger setup,S2 gain, . . .

Conclusion and Future Work


• XENON100

• Many upcoming analyses, stay tuned

• AmBe calibration just finished, taking dark matter data

• XENON1T starts construction this summer

• XeCube2: demonstrated the usefulness of the Compton coincidence technique to measure thescintillation response of LXe to low-energy ERs

• neriX: new dual phase LXe detector built and operational

• Trial measurement shows good promise for the upcoming real measurement

• Hardware changes:

• Install new Hamamatsu 1” multianode PMTs (R8520-406-M4) for the top array

• Replace current bottom PMT with higher QE PMT (R6041-406)

• Focus on measurement of the scintillation and ionization yield of ERs down to ∼1 keV

• After ER measurement completed, continue program with scintillation and ionization yield ofNRs

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