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Apr 15, 2023 138 likes •427 views

Status of the ArDM experiment Filippo Resnati (ETH Zurich) on behalf of the ArDM Collaboration LIDINE 2013, FNAL, 29-31 May 2013 Collaboration ETH Zurich A. Badertscher, F. Bay, C. Cantini, A. Curioni, U. Degunda, S. Di Luise, A.

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SLIDE 1

Status of the ArDM experiment

Filippo Resnati (ETH Zurich)

  • n behalf of the ArDM Collaboration

LIDINE 2013, FNAL, 29-31 May 2013

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SLIDE 2

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Collaboration

  • ETH Zurich
  • A. Badertscher, F. Bay, C. Cantini, A. Curioni, U. Degunda, S.

Di Luise, A. Gendotti, S. Horikawa, L. Knecht, D. Lussi, S. Murphy, G. Natterer, K. Nguyen, L. Periale, F. Resnati, A. Rubbia, F. Sergiampietri, D. Sgalaberna, T. Viant, S. Wu

  • CIEMAT
  • M. Daniel, B. Montes, L. Romero, R. Santorelli

2

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SLIDE 3

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Outline

  • Argon as a target for WIMP direct detection
  • ArDM recent past
  • Pulse shape discrimination (old runs)
  • Material screening
  • Neutron background and passive shielding
  • Status of the detector
  • New TPB coating performance
  • Installation of the detector in Canfranc
  • First test in warm GAr underground and expected light yield
  • Conclusions and outlooks

3

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SLIDE 4

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Argon as target

  • Extensive experience as

detector medium (neutrino experiments).

  • Cheap, easy to handle and to

purify (large volumes).

  • Event rate less sensitive to

energy threshold than for heavier noble gasses.

  • PSD and charge/light

(ß/γ background rejection).

  • 39Ar in atmosphere

(ß-active isotope, T1/2 = 269 y, Q = 565 keV, ~1 Hz/kg).

4

Xe Kr Ar Ne

Fast component Slow component

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SLIDE 5

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Direct WIMP detection

  • WIMPs (elastic) scatters on Ar

nuclei.

  • Nuclear recoils (<200 keV)

excite and ionize surrounding argon atoms.

  • Detection of scintillation light:
  • VUV (~128 nm) photons + WLS + PMTs.
  • Detection of ionized charge:
  • e- drift + extraction to the vapor +

proportional scintillation.

  • charge can be amplified in gas and directly

readout (LEM).

5

LAr GAr

with double phase TPC

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SLIDE 6

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

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

ArDM

6

  • ~1 ton double phase argon TPC for direct DM searches.
  • Presently installed in the Laboratorio Subterráneo de Canfranc.
  • Drift length: 120 cm.
  • Diameter: 80 cm.
  • Target mass: 850 kg.
  • Neutron shielding: passive

polyethylene.

  • Argon purification: LAr and

GAr recirculation through getters.

  • Temperature control: vacuum

insulation + two cryo-coolers.

  • Light readout: 12 PMTs in LAr

+ 12 PMT in GAr (8“ Hamamatsu R5912-02MOD-LRI).

  • Charge readout: proportional

scintillation in vapor (eventually Large Electron Multiplier).

  • A. Rubbia, J. Phys.: Conf. Ser., vol. 39, pp. 129–132, 2006

30 keVer threshold 0.5 ev/ton/day

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SLIDE 7

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Phased approach

  • Surface operation:
  • Build and assemble the ArDM prototype (extensive R&D efforts).
  • Commission the detector cryogenics, purification, HV, electronics,

light readout and software.

  • Underground operation I:
  • Construction and installation of the passive neutron shielding.
  • Installation of ArDM and its infrastructures (finished in March 2013).
  • Warm gas argon runs (test light readout system) - ongoing.
  • Cold gas argon runs (test cryogenics, light readout, impact on the lab

environment, ...).

  • Underground operation II:
  • Liquid argon tests (commission HV, purification, cryogenics, ...).
  • Physics runs (beginning 2014).

7

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SLIDE 8

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Pulse shape discrimination

LAr run on surface with only 14 PMT array below the cathode

241Am-Be source (externally triggered tagging the γ with a NaI)

8

neutron gamma Fast O(10 ns) Slow O(1.6 μs)

PSD parameter is the component ratio: fast/(fast+slow) neutron -> “fast” ß/γ -> “slow”

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SLIDE 9

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Pulse shape discrimination

9

241Am-Be

  • neutrons: < 11 MeV

(max Ar recoil ~1 MeV)

  • γ: 4.4 MeV

1 MeVre ~ 175 p.e. @ 0.7 p.e./keVee

Entries 18776

component ratio 0.2 0 .4 0.6 0 .8 1 counts/bin 200 400 600 800 1000 1200 1400 1600 1800

Entries 18776

Na source

22

after background subtr action function) fit (gaussian and expon ential

Entries 30216

component ratio 0.2 0 .4 0.6 0 .8 1 counts/bin 200 400 600 800 1000 1200 1400 1600

Entries 30216

Am-Be source

241

after background subtr action

  • exp. and gaussian func

tion) fit (gaussian and sum o f

22Na 241Am-Be

total collected light (p.e .) 200 400 600 800 1000 component ratio 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

CR_Histo_2D Entries 48813 Mean x 192.2 Mean y 0.426 RMS x 257.6 RMS y 0.2043

10 20 30 40 50 60 70 80 90

CR_Histo_2D Entries 48813 Mean x 192.2 Mean y 0.426 RMS x 257.6 RMS y 0.2043

n γ

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SLIDE 10

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Pulse shape discrimination

total collected light (p.e.) 20 40 60 80 100 120 140 160 electronic recoil contamination

  • 7

10

  • 6

10

  • 5

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10

measured electronic recoil contamination (ArDM average pulse shape) contribution from the photoelectron statistics (pulse shape from W. Lippincott, et al.) contribution from the photoelectron statistics

10

Measured fraction of 22Na source events mis-identified as neutron. Light yield estimated for the present configuration: 2 p.e./keVee Contamination expected: O(10-3) @ 10 keVee (statistical fluctuation only) Additional rejection factor from charge to light ratio (measure foreseen during the underground operation) Natural and cosmic induced background biases the measure -> to be evaluated underground

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SLIDE 11

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Material screening

11

Cryogenic and low activity Hamamatsu R5912-02MOD-LRI

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SLIDE 12

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 12

Material screening

Measurement campaign with Ge detector supported by the LSC

Already measured:

  • PMT (glass / dynodes / base)
  • Drift cage resistors

Measurement foreseen:

  • Stainless steel of the vessel
  • Parts of the field cage

Raw gamma spectrum

Contaminations are input to evaluate the neutron flux inside the detector (irreducible background) -> Ongoing

Simulation (SOURCES)

  • f 1 ppb 238U in stainless

steel 10-12 n/s/cm3

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SLIDE 13

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Neutron background in the cavern

13

“External” sources of neutrons:

  • Natural isotopes (spontaneous

fissions and (α,n) reactions)

  • cosmic muon

(spallation reactions) Neutron flux and energy spectrum “before the shielding” are essential input parameters for the complete Monte Carlo simulation In collaboration with Nuclear Innovation Unit (CIEMAT)

liquid scintillator BC501A

Detector tested at CIEMAT and to be moved in LSC

252Cf

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SLIDE 14

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Passive shielding

14

  • Lateral shield partially installed (allow to work on the top flange).
  • Bottom shield ready to be shipped to LSC.
  • Top shield assembled in CIEMAT (load test ongoing).
  • 50 cm thick polyethylene shield

reduces the flux of neutron below 1 MeV by a factor of ~105

  • Evaluate neutron interaction

rate in ArDM -> need of the measurement of the neutron flux in the cavern (ongoing)

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SLIDE 15

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

New Vs Old coatings

15

500 1000 1500 2000 2500 3000 3500 4000 100 200 300 400 500 600 700 800 900 1000

New Old τ3 (ns) # p.e.

TPB very good WLS solution for LAr applications. R&D to chemically attach it on Makrolon (paper in preparation) Evaporated TPB requires careful handling, minimize exposure to UV light and air 24 PMTs and reflectors re-coated. Test in warm GAr with a 241Am α source. Comparison of the same PMT before and after the re-coating. Detection efficiency improvement: ~5x.

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SLIDE 16

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Installation (PMTs)

16

PMT layout PMT independently mounted Completed PMT array (Zurich) In the boxes ready to be shipped TPB 0.1-0.2 mg/cm2 PMTs coated and tested at CERN mounted at ETH (Zurich).

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SLIDE 17

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Installation (reflectors)

17

Evaporator (Valencia) Unpacking (LSC) TPB ~1 mg/cm2 Tetratex sewed on Vikuiti Side reflectors prepared at CERN and coated at IFIC (Valencia).

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SLIDE 18

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Mounting the detector

18

March 2013

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SLIDE 19

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

First GAr test underground

19

Short α track Long α track

Mylar sealed 241Am source (~500 Bq) custom made at CIEMAT installed in the active volume of ArDM.

  • ~5 MeV α @ 100 Hz in the active

volume.

  • 60 keV γ @ ~1 Hz in the active

volume. α events well localized:

  • Z coordinate scan with the source

facing downwards.

  • 9 days of data-taking (~5 h/day)
  • GAr (99.9999% pure) filling and

evacuation every day. Measurement of the light yield of the newly coated detector fully assembled

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SLIDE 20

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Electronics

20

12x PMTs Passive splitter Analog sum Threshold discr. Coinc. unit ADCs 12x 12x 12x 12x 12x Timing unit PC & storage

  • VME based electronics.
  • CAEN crate and modules

including 4x ADC V1720, 8ch, 12bit, 2Vpp, 250MS/s. Trigger on the coincidence

  • f the top and bottom PMT

arrays with a threshold of 1.75 p.e.

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SLIDE 21

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

LED calibration run number 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 Integrated pulse height for single p.e. [arb.] 20 40 60 80 100 120 140

9 days

pulse integral (a.u.) time

PMT calibration

21

  • PMT response stable over 9

days: 2.5x107 (gain within 5%) continuously monitored.

  • Dark rate (2 PMT

excluded): top array: ~9 p.e. / 8 μs bottom array: ~2 p.e. / 8 μs

  • ~5 keVee threshold (11 p.e.

@ 2 p.e/keV) from the dark counts.

PMT number 2 4 6 8 10 12 14 16 18 20 22 24 s] µ Average dark counts [1/8

  • 1

10 1 10

2

10

dark rate (1/8 μs-1)

Top PMT array Bottom PMT array

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SLIDE 22

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Light yield [p.e.]

500 1000 1500 2000 2500 3000 3500 4000

TTR

0.2 0.4 0.6 0.8 1 1.2 1 10

2

10

Alpha events

alpha track source holder (PTFE) alpha track source holder (PTFE)

“short track”

22

TTR: top/(top+bottom) ~ Z position “long track”

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SLIDE 23

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Source @ the cathode

23

Light yield [p.e.]

200 400 600 800 1000

TTR

0.2 0.4 0.6 0.8 1 1.2 1 10

2

10

α long tracks 35 Hz α long tracks hitting the cathode grid α short tracks ~40 Hz

Light yield [p.e.]

500 1000 1500 2000 2500 3000 3500 4000

TTR

0.2 0.4 0.6 0.8 1 1.2 1 10

2

10

α from the top PMTs < 0.1 Hz background ~15 Hz

material in the detector, environmental radioactivity, γ from the 241Am, ...

dark counts (~11 p.e.) ~15 Hz (compatible with p.e. statistics)

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SLIDE 24

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Position Scan

24

total light yield [p.e]

500 1000 1500 2000 2500 3000 3500

TTR

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

  • 5

10

  • 4

10

  • 3

10

24.5 cm above cathode total light yield [p.e]

500 1000 1500 2000 2500 3000 3500

TTR

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

  • 5

10

  • 4

10

  • 3

10

45.5 cm above cathode total light yield [p.e]

500 1000 1500 2000 2500 3000 3500

TTR

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

  • 5

10

  • 4

10

  • 3

10

66.5 cm above cathode total light yield [p.e]

500 1000 1500 2000 2500 3000 3500

TTR

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

  • 5

10

  • 4

10

  • 3

10

87.5 cm above cathode

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SLIDE 25

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Am source distance from cathode grid [cm] 20 40 60 80 100 Light yield [p.e.] 500 1000 1500 2000 2500 3000 3500 4000 4500 Total Bottom Top

Light collection uniformity

25

  • Top/bottom “naive” dependence on the source position.
  • Uniform total collected light (10 % variations): ~3000 p.e. @ ~5 MeV α

Old tests of prototype with 14 PMTs below the cathode:

  • GAr test with 241Am source:

850 p.e. (Now 3x better)

  • LAr test with 22Na source at

0 kV/cm: 0.7 p.e./keVee Extrapolating new light yield in LAr at 0 kV/cm: > 2 p.e./keVee (compatible with Geant4 simulation)

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SLIDE 26

Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013

Conclusions and outlooks

26

  • The ArDM detector is installed underground at LSC
  • First measurement of light yield of the newly coated detector:
  • uniform collection light ~3000 p.e. for ~5 MeV α in GAr
  • Expected light yield in LAr at 0 kV/cm: 2 p.e./keVee
  • 850 kg of Ar, uniform light collection and 30 keVre threshold
  • Next steps:
  • warm gas argon tests with different sources.
  • cryogenic tests in gas argon (learn how to operate the detector

underground)

  • LAr run (full commissioning)
  • Beginning 2014: first ArDM physics run
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SLIDE 27

Backup slides

27

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SLIDE 28

Monte Carlo simulation

Full detector simulation of ArDM using Geant4

TTR Light yield [arb.] 58 cm above cathode

Full detector geometry : PMTs, reflectors, TPB layers, support structure, 3-layer stainless steel vessel wall Ionization and scintillation processes in argon media (gas or liquid) Optical photon tracing involving all the optical processes : wavelength shifting (conversion of VUV photons to visible) definition of all the “optical surfaces” (refraction, reflection ...) PMT response to visible photons The ArDM Monte Carlo simulation includes ; Simulation of the GAr data is on the way