ArDM - LAr on the ton scale

DM16 UCLA Feb. 19th 2016 C. Regenfus ArDM 1

ArDM - LAr on the ton scale ETHZ led collaboration with! CIEMAT, LSC, CERN and others

Installed at Laboratorio subterraneo de Canfranc (LSC)

First ton scale LAr detector in operation

Exploring the low energy frontier of the LAr technology at the ton scale

LSC Exp-08ArDM

Christian Regenfus - ETHZ(On behalf of the ArDM collaboration)

~2500mH2O


Experimental program and time line

ArDM is a R&D facility for future large LAr projects (DS20k)

- Developments done at CERN — synergetic with large LAr facilities (ν-programs)!

- Installation at the Spanish underground site Canfranc (LSC)!

- Design and commissioning for full remotely controlled operation!

- ArDM reconfirmed as a CERN Recognized Experiment (RE18)!

- Collaborating with DS group (e.g. Princeton, APC Paris, LNGS)!

- Common developments towards G2 (DS20k) and G3, depleted argon research

• End 2014: ArDM fully embedded in safety environment of LSC — filling started!

• Summer 2015: ArDM completed first physics run (single phase)

~ 6 months of stable data taking (Run I) !

• Analysis tools and MC framework developed by means of exploiting this data!

• First fundamental analyses have been performed focussing on backgrounds !

• 2016: Preparation of double phase running ongoing — Run II!

• 2017 and beyond — long term data taking — exp. upgrades (light read out) !

• Extended program: 39Ar studies, prototype tests, BG studies….


ArDM in a nutshell

• LAr mass: ~2t total, 850kg active, ~500kg fiducial • Double phase, vertical TPC (0.1 – 1 kV/cm drift field) • Cryogenic low radioactive 8” PMTs 12 + 12 (liquid and gas) • Projected LY ~2pe / keV (@ LAr operation) • Passive external neutron shield (~20t) • Trigger rate / DAQ capability ~ kHz

Dri

ft le

ngth

~11

0 cm

Cathode grid

Top PMT array !in vapour phase

Drift cage (field shapers)

lined with side reflectors

Bottom PMT array immersed in liquid

argon

- PSD and Ionization / scintillation ratio!- Localization: (fiducial volume, 3D imaging)!- Topology: (e.g. multiple elastic scatters from neutrons)

Background recognition strategies:

A.Rubbia J.Phys.Conf.Ser 39:129-132,2006.

Total LAr mass: ~2t

Status of ArDM-1t: arXiv:1505.02443


A ton scale LAr DM experiment

3.13$ 0.45$

5.36$

0.95$2.54$

9.87$

SS$Dewar$

SS$Top$Flange$

HV$resistors$

PMT$Electrode$

PMT$Base$

PMT$Glass$

)2

(GeV/cWIMP

M20 30 40 100 200 300 1000

)2

cross section (cm

-4710

-4610

-4510

-4410

-4310

-4210

-4110

-4010

-3910

XENON100, 225d

Trotta et. al., 2008, CMSSM Bayesian: 95% contour

Trotta et. al., 2008, CMSSM Bayesian: 68% contour

ArDM, (0.22 + 0.08) n/day, 90% CL.

no systematic error included

ArDM: 508kg FV, 3y exposure, 50 < E < 100 keV

Projected sensitivity for BG expectation of (0.22 ± 0.08) n/d (MC)

ArDM: 508kg FV, 3 y exp., 50 < E < 100keV

Multiple scatters

Single scatter neutrons !(indistinguishable BG)

G4 neutron MC

1st task — verifying these points

In the research focus:

Experimental upgrades foreseen

- DUV properties of large LAr targets !

- Neutron interactions!

- 39Ar PSD studies!

- Classification of depAr batches

Expectations!

• Serious contribution to searches of higher mass WIMPs!

• Design parameters for LAr G2 and G3 future facilities!


Stable data taking over ~6 months — 3×109 triggers recorded to disk

Date06.03. 05.04. 05.05. 04.06. 04.07. 03.08.

Inte

grat

ed n

umbe

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ecor

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Perlite removal

Closing of PE shield

Fast DAQ period

PE shield open

PE shield closed

Full: Feb 19th Cryo-cooling system stopped: Aug 5th

Trigger rate: 1.3–2.1 kHz , event size: 66 kB!

DAQ rate: 85–138 MB/s!

3.3 billion triggers — 215 TB raw data

Operation of ArDM — Run I in single-phase LAr mode

Fully remotely controlled, e.g. from CERN

Experiment at LSC ( Canfranc / Spain )

ArDM Control Center CERN

Safety: sophisticated PLC SC system

2015

Date24.02. 26.03. 25.04. 25.05. 24.06. 24.07.

[n

s]

3

800

1000

1200

1400

Stable purity

DM16 UCLA Feb. 19th 2016 C. Regenfus ArDM

TTR0.2 0.3 0.4 0.5 0.6 0.7 0.8

light

yie

ld

[ pe

/ keV

]

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Kr83Co57Ar39

Injected into vapor phase — diffusion time!

tot LY (PE)0 50 100 150 200 250 300 350 400 450 500

TT

R

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LY comparison [pe/keV]

39Ar BG subtracted

LAr: Expected 2 pe/keV

LAr

83Kr signals

- main calibration tool !- well matched to ROI!- many features emerge

cold GAr

~ 1 pe/keV

GAr LY, width, uniformity OK LAr : LY lower uniformity OK width larger

~ 1.1 pe/keV

Top

Bottom

0.6 < TTR < 0.7

LAr

LAr

Top

Bottom

LY and shapes: evidence for DUV absorption — under study O2 - N2 - trace measurements — negative result ICP mass spectrometer analysis under way However: question of purity only —> filters, distillation….


f90

48 hours data taking — ~30M events — no fiducial cuts

39Ar

The full LAr target (850kg active)252Cf neutron data

separation power (gaussian assumption)

Looking into one of the main features of LAr — PSD

preliminary

Need double phase data to proceed

50%

99.7%

polluted with γ absorptions

Very high if LY good

Good fiducialization is important


Exploring external γ backgrounds

Estimate comparable with LSC parameters (Ge measurement)

0 500 1000 1500 2000 2500 3000 3500 4000 4500 500010

−6

10−5

10−4

10−3

10−2

10−1

100

Difference spectra of external BG (open − closed)

Number of PE

Rate

per

10P

E

Data MC U238 (0.95211) MC TH232 (0.84792) MC K40 (1.1721) Fit (Σ MC)

Fit range

Data from open - close top cover !

Spectrum well described by 238U, 232Th and 40K contributions

preliminary

Large target feature:!!Selfshielding!!Spectrum extends into higher energy range!!(mult. γ absorption)


MC efforts

ArDM G4 model

Detector simulation developed and tuned with data of Run I

• Full optical photon ray tracing for DUV (scintillation) and visible (wave shifted) light!

!!!

• Optical parameters tuned to data! ! (scatt. length, absorption, refl. coefficients)!

Screening results used for e-like and n-like MC to estimate backgrounds

TTR vs TotLY

• MC data fully digitized !

• Same reconstruction and analysis framework!

• MC is in a good agreement with data, typically to better 10% !

• Main features are reproduced

Containing all known BGs

TPB surfaces Angular effects


e - like spectra

total light yield [pe]0 1000 2000 3000 4000 5000

rate

[ Hz

/ 10

keV

]

-510

-410

-310

-210

-110

1

10 -- 845.8 Hzγar39 +

data : 828.7MC : 845.8ar39 609.2tank 26.3pmtGlass 10.4topFlange 5.6pmtBase 8.9fieldShaperRing 1.3fieldShaperPillar 6.5external 177.7

Based on MC response from screening

validates our low BG goals

Data well described by normalized MC spectra based on the material screening results + external BG

73% 39Ar!21% external!6% internal

850 kg LAr target (~ 610L ) — no fiducial cuts850 Hz {

MC {Datapreliminary


Projected 39Ar sensitivity of ArDM for a 3σ measurement

Measurement time for a given sensitivity

measurement on 10-5 level feasible — improvements, e.g. more sophisticated analysis (spectral fit)

10s 1m 1h 1d 10d 100d

101 102 103 104 105 106 107 10810−6

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10−4

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Measurment time [s]

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letio

n fa

ctor

sen

sitiv

ity

500LFiducial volume

300L200L100L

BG rate 10Hz

~ ext + int !present setup

with additional external shield

3 months

10-5

Characterization of depleted argon


Hardware preparations/upgrades for Run II

130 cm

array of 13ceramic crucibles

pumping flange

access flange

vacuum gauge

vacuumvessel

reflector sheet120 x 25 cm2

Figure 11. 3D sketch of the evaporation apparatus for the reflector sheets of the ArDM detector.

Time [hrs]0 0.5 1 1.5 2 2.5 3 3.5

Pre

ss

ure

[m

ba

r]

-510

-410

-310

Pressure during evaporation

Figure 12. During the evaporation we constantly monitored the pressure of the evaporation vessel.The second peak shown in the graph, roughly after� 4 hours, is interpreted as the moment in whichno more TPB is remaining in the crucible.

4.2 Assembly of the wavelength shifting light reflectors in ArDM

The wavelength shifting side reflector is made of 15 overlapping panels, each of whichis composed of a TTX reflector installed on 3M foil substrate which acts as a substrate,providing mechanical support and avoiding curling of the edges due to the high thermalshrinking coefficient of TTX. The panels were fixed on the first and last field shaper ringsby means of teflon clips. The reflectors were installed such that they overlap slightlyon their edges and produce a uniform reflector around the detector volume. UV lampillumination results in a clear fluorescence (See Figure 14).

The mechanical support of the photomultipliers can easily be adapted to support mostof the commercially available 8" hemispherical PMTs. Bialkali photocathodes become

– 13 –

Cold charcoal trap

TPB coatings

ITO layer + TPB coating

Large ITO + TPB ! coated PMMA plates

New TPC drift cage, HV system !

Replace TPB coated surfaces!

Implement ITO coated windows!

Introduce cold charcoal trap!

Add cryo link (liquid storage)

HV up to 100kV

Activities ongoing at CERN and CIEMAT

Charge signal

Light yield

Fiducialization

R&D program

α background


Light detection system upgrade — under study

- Large capacitance!!- Light concentration

possibilities ?

Ar PS reconstruction (SiPM vs PMT avg traces)

SiPMs love low temperatures

Time from Trigger [s]4− 2− 0 2 4 6 8 10 12 14

6−

10×

Pu

lse

He

igh

t [V

]

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Waveform for Single EventSiPM

PMT

Total LY

μ

α

saturation

β/γ

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st

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ht

fra

cti

on

0 100 200 300 400 500 6000.3

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Demonstration for PID by PSD in SiPM LAr test

- Present system based on 24 8” PMT good, but: ! low PDE (17%), large amount of glass!

- Upgrade not trivial — m2, cryog., PDE, fast, power !

- Option Hamamatsu R11065 (30%) still under ! discussion (stability?, fill factor)!

- SiPM solution tempting — still need some time

SiPM: digital device with analogue read out

Prototype low power PA

Towards large surfaces - first array tests


Conclusions and outlook

• ArDM successfully completed first physics data taking (Run I) in single phase mode!! 3×109 triggers recorded to disk during ~6 months of stable data taking. Preliminary!! analyses based on the first data sample (<5%) confirm the expected performance of!! the ArDM detector — full statistics analyses ongoing!!• A detailed MC model was developed, describing the detector from first principles. Tuning of

parameters indicate a relatively short DUV absorption length in the LAr (ongoing)!!

• A fully satisfactory description of e-like background in the LAr target was obtained!• 39Ar β-decays quantified in agreement with the expected value of ∼1 Bq/kg !• The second most dominant BG due to external sources, internal contribution ~6% !!

• PSD promising (need double phase data to proceed)!!

• Presently preparing double phase Run II — scheduled for 2016!!

• 2017 and beyond!• Accumulate statistics — further hardware upgrades planned!• Facility available for sensitive depleted argon studies (sensitivity level down to 10-5)!• Full scale demonstration at the ton-scale is a necessary step towards 10-ton scale and beyond

ArDM - LAr on the ton scale

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