The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

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The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration

Transcript of The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Page 1: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

The DEAP-1 Detector at SNOLAB

Chris Jillings, SNOLAB/Laurentian U.

For the DEAP/CLEAN Collaboration

Page 2: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

The DEAP-1 Detector

Nuclear recoil

Electron recoil

Page 3: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

DEAP-1 at Queen’s

arXiv:0904.2930

Demonstrated a pulse shape discrimination between electron recoils and nuclear recoils at ~4x10-8

Detector stability(120-240 pe)

Measured at 511 keV2.9

2.7

2.8

Page 4: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

DEAP-1 moved to SNOLAB in 2007

• Runs underground: – December 4, 2007 to January 2008– v1 clean chamber: July 4, 08 to Dec 6, 08– v2 clean chamber: March 19, 09 to Dec 10, 09– v3 clean chamber: March 25, 10

• PSD improved to ~ 10-8

• Light yield increased using HQE PMTs• Backgrounds in WIMP energy ROI greatly

reduced

Page 5: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Clean v1 chamber

Glove box preparation of inner chamber (reduce Rn adsorption/implantation on surfaces)

Page 6: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

222Rn introduced from gas bottle, settles to about 25 decays per day

alpha

222Rn in DEAP-1 (Gen 1)

Page 7: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

DEAP-1 Gen 2 chamber

• DEAP-1 inner chamber redesigned, teflon as reflector instead of TiO2 paint

• Radon trap installed for filling

Gen 1 chamberGen 2, no Rn spike and ~10 times cleaner

Page 8: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Stability (Generation 2)

Stable to 10% over 150 days

Gen 2 data taken with new DAQ

Page 9: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Gen 3: Improved light yield

v3, ~4.7 pe/keV

v2, ~2.5 pe/keV

60 keV gammas from 241Am in AmBe neutron calibration runs

Page 10: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Hamamatsu R5912 HQE PMTs

• Qualified two of each candidate 8” PMT• Evaluate gain, relative efficiency, dark rate,

timing, late pulsing, after pulsing, prepulsing, magnetic field sensitivity ....

R5912 HQE will be used for DEAP-3600.

PMT in testing facility at Queen’s

5912 SPE

<75 ppb U/Th forR5912

Manufacturer Model No. Eff. Relative to R1408

Hamamatsu R1408 (SNO) 1.00

Hamamatsu R5912 1.30

Hamamatsu R5912 HQE 1.40

Photonis XP1806 1.18

Electron Tubes ET9354KB 1.20

Page 11: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Background rates in DEAP-1 versus time

v3 data being analyzed

120-240 pe region

Page 12: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Background Questions

• Given the efforts at surface cleaning between Gen 2 and Gen 3 yielded small results, is there a source of low-energy backgrounds we are missing?

• Is the WIMP-region background caused by radon in the bulk?

• Or quantitatively: what is the event rate in the WIMP region induced by radon in the bulk?

• A sample of radon extracted from approximately 100 litres of air, after corrections for efficiencies, should add Bq levels of radon.

Page 13: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Radon Spike From Air

Procedures and equipment from SNO.

InletNaOH

Water trap(coils at -60C)

ChromaSorbTrap at -110C(ethanol slush)

Lucas cellDEAP Rn tube

Page 14: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Radon Spike

• Use high-flow trap with chromasorb at -110C to trap 222Rn.

• Oxygen, nitrogen and argon pass through trap.• Transfer radon with cryopumping to small trap• Volume expand radon into Lucas cell and Rn tube.• Count Lucas cell to measure Rn spike.• Next day: install on inlet to argon system.

• As long as only a few standard cc’s of contaminant gas, our SAES purifier will purify.

• Concentrating the radon in 1m3 of air is not considered a “source” by SNOLAB.

Page 15: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

PSD Underground

• PSD is a huge data-reduction effort• Depends low-noise electronics• We have 27 TeraBytes of MIDAS data.

DAQ SamplingData Rate

Ev/sec

Data Rate

Mbyte/secBottleneck

Scope500 MHz

10 sec<~150 /s 1 Scope readout

V1720 &

MIDAS

250 MHz

16 sec~350 /s 8

Source strength

Page 16: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Sample PSD Data

Page 17: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Background To PSD

• The detector high-Fprompt background rates have some probability of being coincident with a valid tag as described in the DEAP-1 Surface paper (arXiv:0904.2930).

• Depends on rate of tags and the time window imposed in analysis.

• We expect:

RunPSD

Entries

Expected #

pile-up events

Surface 17 M 0.26

U/G 2008 (scope) 22 M 0.16 (preliminary)

U/G 2009 (MIDAS) 70 M 0.13 (preliminary)

Total 109 M 0.45

Page 18: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Analyzed PSD

Page 19: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Future PSD

• Surface, Gen 1 and Gen 2 data u/g had the same light yield. Analysis of Gen 3 PSD will allow the relationship between energy and PSD to be explored as well as effects of photon counting.

• Would like few x 109 events background free.• Requires

– Optimized tagging– Stronger source

Page 20: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

New 22Na source

Place source in bicron BC-490 plastic scint in mold.

Double-tag:

1- positron in plastic

2- back 511keV1 cmPMT

12

Source in design stages. Early testing with BC-490 successful.

Page 21: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Neutron-Shielding/M.C. Tests

• A series of runs were taken with the SNO AmBe neutron source behind various thicknesses of plastic

• Model test– Neutron spectrum from AmBe source (Neutron energy

spectrum from AmBe source depends on the grain sizes.)– neutron shielding Monte-Carlo calculations CLEAN nuclear-recoil quenching factor.

• Analysis ongoing

Fixed source holder

Frame holds from0.25” to 2” HDPP

Page 22: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Some Notes About Analysis

• Switching PMT and base circuit forced change in baseline algorithm.

• PMT SPE mean charge was determined using a mean charge over a restricted integration window. We have developed fits to Polya functions.

• Software noise-reduction techniques developed.• Re-analysis of all SNOLAB data just underway.• Goal: submit manuscripts for publication in timely

way.

Page 23: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

DEAP-1 to DEAP-3600

• Light yield in DEAP-1 + Monte Carlo Light yield in DEAP-3600 > 8 pe/keV (with R5912 HQE PMTs)

• Stability of DEAP-1 suggests that continuous purification of Argon not needed in DEAP-3600 (but it is available)

• PSD data are consistent with surface results: PSD model used holds up.– Detailed analysis of Gen 3 PSD underway. This is important

because PSD depends on statistics of photon counting and energy.

• PMT/Electronics for DEAP-3600 prototyped on DEAP-1– We are likely to go to a tapered base to improve signal linearity.

• Measured backgrounds in DEAP-1 allow for DEAP-3600 with reduced FV to be useful.

• Re-assembly of DEAP-1 in J-drift after with cleaned plumbing and new chamber.

Page 24: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Next 12 Months

• Move to J drift• Gen 4 acrylic chamber

– Better control of neck events– Wash all argon plumbing lines– Small improvements to cooling system

• Hotter source for PSD with improved time tag

Page 25: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.
Page 26: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

SNOLAB

• SNOLAB has provided – Services (IT, logistics …)

– LN2,

– technical staff, – engineering support, – URAs,– funds for new source development – extra shifts, …

Page 27: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

People

• DEAP-1 slides shown here are drawn from work by many including people at…– LU/SNOLAB (incl 9+ URAs in past three years)– Queen’s– Alberta– TRIUMF– Carleton– Yale– U. North Carolina– U. New Mexico– LANL

Page 28: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.
Page 29: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Position reconstruction

Size of DEAP-1

Very good position reconstruction, useful for identifying surface background events

Page 30: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Background rates in DEAP-1 (120-240 pe)

Date Background Rate (in WIMP ROI)

Configuration Improvements forthis rate

April 2006 20 mBq First run (Queen’s) Careful design with input from materials assays (Ge couting)

August 2007 7 mBq Water shield (Queen’s) Water shielding, some care in surface exposure (< a few days in lab air)

January 2008 2 mBq Moved to SNOLAB 6000 m.w.e. shielding

August 2008 0.4 mBq Clean v1 chamber at SNOLAB

Glove box preparation of inner chamber (reduce Rn adsorption/implantation on surfaces)

March 2009 0.15 mBq Clean v2 chamber at SNOLAB

Sandpaper assay/selection, improved purging, PTFE instead of BC-620 reflector (from Rn emanation measurements), Rn diffusion mitigation, UP water in glove box, documented procedures;Rn Trap@SNOLAB for filling.

March 2010 ? Clean v3 chamber at SNOLAB

Acrylic monomer purification for coating chamber. TPB purification.

Table from Mark Boulay

Page 31: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Alpha backgrounds

• Are very high energy• Non-linear energy response must be

calibrated out.

Page 32: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Clipping of Prompt Light

Average alpha

Average low energy recoil scaled to alpha energy

• Protection diodes clip the pulse

• Clipping is necessary to observe alphas and low energy recoils in the same run for DEAP-1 (clipping will be rare in DEAP 3600)

• New energy scale required for alphas

Page 33: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Energy Non-linearity

• Each PMT sees a >50% change in light based on event vertex position

• With clipped pulses, the effective gain may be highly non-linear over this range

• Methods to deal with this:1.Correct for clipping (currently gives ~10% energy resolution)2.Develop independent alpha energy scale (currently gives ~3% energy resolution)

Page 34: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Radon Daughter Coincidence Tags

232Th Chain238U chain

• Timing coincidences for alpha decays give calibration points for the alpha energy scale

Page 35: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Radon 220 Coincidences

Fit T½ = 0.15 ± .02 sReal T½ = 0.15 s

220Rn

216Po

Page 36: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Polonium 214 Coincidences

Fit T½ = 163 ± 27 usReal T½ = 164 s

214Po

214Bi

Page 37: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Correcting for Nonlinearity

Page 38: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Correcting for Nonlinearity

Corrected Prompt = Total Prompt _1 – 0.05 PromptZ + 1.33 PromptZ2

PromptZ = Prompt0 – Prompt1 Prompt0 + Prompt1

Page 39: The DEAP-1 Detector at SNOLAB Chris Jillings, SNOLAB/Laurentian U. For the DEAP/CLEAN Collaboration.

Calibrated Alpha Spectrum

Daughter Constrained Fit Unconstrained Fit222Rn 267 ± 14 325 ± 54218Po 267 ± 14 214 ± 20214Po 41 ± 7 42 ± 9 210Po 35 ± 18 2 ± 58220Rn 68 ± 7 123 ± 35216Po 68 ± 7 54 ± 9212Po 20 ± 10 20 ± 10

Χ2/dof 83/60 67/58

All widths are set at 2.9%