PDF Status of the DEAP-3600 experiment

Status of the DEAP-3600 experiment

Marcin Kuźniak

on behalf of the DEAP-3600 collaboration

Outline

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Detector overview

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Current status

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Latest dark matter search result

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Pulseshape discrimination C.Jillings (poster session 1)

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Limiting backgrounds

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Hardware upgrade

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Science highlights

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EFT and galactic halo models A. Zúñiga (Monday, 17:10)

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Heavy dark matter particles M. Lai (Monday, 17:10)

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Summary

DEAP-3600 Collaboration

~95 researchers in:

Current landscape

J. Billard et al., APPEC Committee Report, arXiv:2104.07634

Spin-independent, with the usual assumptions: Standard Halo Model, isospin parity

DEAP-3600 Dark Matter Search

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3.3 tonne liquid argon target (1000 kg

fiducial) in sealed ultraclean Acrylic Vessel

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128 nm scintillation from liquid argon is detected after converting it to visble

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In-situ vacuum evaporated TPB wavelength shifter (~10 m

surface)

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Bonded 50 cm long light guides +

polyethylene shielding against neutrons

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255 Hamamatsu R5912 HQE PMTs 8-inch (32% QE, 75% coverage)

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Detector immersed in 8 m water shield, instrumented with PMTs to veto muons

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Located 2 km underground at SNOLAB

3279 kg LAr

SNOLAB

Situated 2 km below the surface (6000 m.w.e.) in the Vale Creighton Mine located near Sudbury, ON.

Muon flux: 0.027 muon/m²/day.

DEAP-3600

Neutron (AmBe)

γ(²²Na)

PMT signal:

Prompt : 0-60ns Late: 60ns-10μs

Pulse shape discrimination (PSD)

Ar singlet and triplet excited states have well separated lifetimes (6ns vs. ~1.5 m s)

Single phase LAr:

scintillation channel is sufficient for b/g rejection no need for the ionization channel

Improved pulse shape discrimination

(accepted for EPJ C)

Conclusions:

1: Reducing detector effects improves effectiveness of PSD algorithms.

2: PSD in DEAP-3600 can reduce 10⁸ events/keV → <0.2 events in the ROI for 3 tonne years.

3: Using demonstrated reduction in ³⁹Ar from underground argon, we can obtain <0.2 events in 3000 tonne years in a large single-phase detector.

→ see poster session 1 (Chris Jillings)

231 live-days dataset (Nov ‘16 – Oct ‘17)

Phys. Rev. D, 100, 022004 (2019), arXiv:1902.04048

● Zero observed backgrounds, leading exclusion with LAr

● Excellent control over main background types, leading edge among other experiments

● Further sensitivity improvements limited by backgrounds from alpha activity in the neck of the detector

● Since then:

● Stable data collection for DM search:

● 802 live days (Nov 2016 – March 2020)

● 80% blind since Jan 2018

● Ongoing MVA/machine learning analysis, with improved signal acceptance and lower backgrounds

Neck alpha backgrounds

Monte Carlo

Data

The optical model in good agreement with data

● Alpha scintillation in LAr film/mist covering the flowguides

● Shadowing effect from the flowguides limiting the solid angle

→Apparent low-energy nuclear recoil events

Hardware upgrade 1: neck events

● Degraded light collection from prompt high energy events shifts them to lower energies, where we look for WIMPs

Solution: WLS with long time constant deposited in the problematic part of the detector a

VUVBare acrylic

a VUV

Coated acrylic

Current configuration Slow wavelength shifter (WLS) coating

Resulting

+

pulseshapes

Dust alpha backgrounds

● Evidence for presence of dust particulates in LAr in the detector.

● Orginally installed LAr filtration loop could not be used for technical reasons

● Alpha decays embedded in dust particulates have reduced energy deposition in LAr

→ low-energy tail in the spectrum

● Scintillation from such events can be partially shadowed by the particulates

Hardware upgrade 2: dust

Alternate cooling system

Objective 1: remove dust particles from LAr

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Deploy stainless steel vauum jacketed pipe to remove LAr and allow for

filtration

Objective 2: remove LAr film from the neck region

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Deploy alternative stainless steel vacuum jacketed pipe through the centre of the neck

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Allows for injection of LAr into the detector with the neck cooling coil turned off

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Warms the neck region so that there is

Hardware upgrade timeline

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New acrylic flow guides sanded and coated at Carleton

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Delivery of new system components for installation u/g:

Fall 2021

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Installation and commissioning work mainly throughout Winter and Spring.

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LAr fill: Spring 2022

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Data taking: Summer 2022

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Comparison and verification of backgrounds post dust filtration and with new neck configuration

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Quantification of neck alpha background using PSD based variables

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Are there backgrounds that persist in the upgraded

configuration?

Effective Field Theory, non-standard halo

P. Adhikari et al. (DEAP-3600 Collaboration), Phys. Rev. D 102, 082001 (2020)

231 live-days results are reinterpreted with a more general non-relativistic EFT framework, and exploring how possible substructures in DM halo affect these constraints

Effects of isospin parity breaking

→ see Ariel Zúñiga’s talk, DEAP-3600 constraints on dark matter effective interactions and halo substructures

P. Adhikari et al. (DEAP-3600 Collaboration), Phys. Rev. D 102, 082001 (2020)

Planck scale mass multi-scattering dark matter

● a.k.a multiply-interacting massive particles (MIMPs)

● DM candidates above -n 10σ𝛘 ≅ ^-25 cm² and m_𝛘≳10¹² GeV lose a negligible amount of energy in the scatterings with the Earth nuclei and can reach underground detectors designed for WIMP search.

● Event signature:

● Contains multiple nuclear recoil scatters

● Apparent low Fprompt (electronic recoil-like event)

MIMP exclusion limits

→ see Michela Lai’s talk, Detection Of Heavy Dark Matter Particles In DEAP-3600

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Freshly submitted to PRL: arXiv:2108.09405

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813 live-days, blind analysis

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New exclusion for candidates at Planck scale masses

(relevant for composite DM models)

Papers published/under review/upcoming

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Constraints on dark matter-nucleon effective couplings in the presence of kinematically distinct halo substructures using the DEAP-3600 detector (Phys. Rev. D, 102, 082001 (2020))

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Pulse-shape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data (accepted in Eur. Phys. J. C, arXiv:2103.12202)

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First direct detection constraints on Planck mass scale dark matter with multiple-scatter signatures using the DEAP-3600 detector (submitted to Phys. Rev. Lett., arXiv:2108.09405)

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Precision Measurement of the Specific Activity of 39Ar in Atmospheric Argon with the DEAP-3600 Detector (collaboration review)

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Technical paper on slow wavelength shifter coatings (collaboration review)

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On the horizon:

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Boron-8 solar neutrino absorption measurement

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Multivariate analysis to improve WIMP signal acceptance

Summary

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Excellent control over

Ar, neutron, radon and surface alpha backgrounds

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Multiple improved or new physics searches on the already collected dataset

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Sensitivity currently limited by the neck and dust alpha backgrounds

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Planned hardware upgrade, allowing to recover the design sensitivity

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Preparations slowed down by the pandemic

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About ready to start now with the installation, to follow until late Spring 2022

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Commissioning and physics run to follow

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Exciting Boron-8 solar neutrino result coming soon, stay tuned!

Electromagnetic backgrounds and a

measurement of

Ar activity