Recent results of WIMP dark matter quest with the DEAP-3600 - - PowerPoint PPT Presentation
XVII Mexican Workshop on Particles and Fields 21 25 Nov 2019 Len, Guanajuato Recent results of WIMP dark matter quest with the DEAP-3600 experiment Ariel Zuiga Reyes* on behalf of DEAP-3600 collaboration *Astrophysics Ph.D. student
XVII Mexican Workshop on Particles and Fields 21 – 25 Nov 2019 León, Guanajuato
Ariel Zuñiga Reyes*
*Astrophysics Ph.D. student (arzure89@gmail.com) Institute of Physics & Institute of Astronomy (UNAM)
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Obligatory DM intro slide
Planck 2015
Stars: optical Gas: X-rays Total mass: gravitational lensing
The Bullet Cluster:
Separation of gas from the bulk
Flat rotation curves of galaxies
matter only.
matter component.
dark matter.
matter clustering.
Mass discrepancies in galaxy clusters when use gravitational lensing
Foreground cluster CL0024+1654 produces multiple images of a blue background galaxy.
Cosmic Microwave Background
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Particle candidates for DM Most experiments
for WIMPs How to detect WIMP? Direct detection
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Dark Matter direct detection Dark matter particles from the Galactic halo that pass through the Earth will occasionally scatter off nuclei. The resulting recoil energy of the nucleus can be measured in dedicated low background detectors.
DM particle
𝐹𝑠 = |𝑟|2 2𝑛𝑂 = 𝑛𝑠
2 𝑤2 1 − cos 𝜄
𝑛𝑂 < 100 𝑙𝑓𝑊
Observable: recoil energy
Angle not measurable so for a given DM speed γ-rays
e-
heat
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: DM velocity distribution boosted to Earth’s frame.
𝑤𝑛𝑗𝑜 = 𝐹𝑢ℎ𝑠 𝑛𝑂 2 𝑛𝑠
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Expected rate of events
Detector physics Minimum velocity Particle/nuclear physics Astrophysics
Typical event rates are < 1 event/kg/year. A great experimental challenge! Differential cross-section
Spin-independent (SI) cross-section at zero momentum transfer Spin-dependent (SD) cross-section at zero momentum transfer
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See arXiv:1902.04048 (Published: PRD)
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Facility located 2 km deep underground at SNOLAB, Canada looking for direct detection of Weakly Interacting Massive Particles (WIMP).
Dark Matter Experiment using Argon Pulse-shape Discrimination (DEAP)
Main features:
provide thermal insulation and shielding.
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Liquid argon is suitable for very large targets due to:
… but there is Ar39: β decays around 1 Bq/kg in natural argon
Argon is a noble chemical element that, at atmospheric pressure and a cryogenic temperature
Argon Pulse-Shape Discrimination approach
Argon singlet and triplet excited states have well separated lifetimes
11 Electron recoil (ER) Nuclear recoil (NR)
fprompt fprompt
signal events have more prompt light!
Nuclear recoils excite predominantly the singlet state
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γ-rays β decays
Surface α decays
Pulse-Shape Discrimination in DEAP
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Background: Overview
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Neutrons can be produced by nuclear reactions in detector components
They may then scatter on argon nuclei and produce a WIMP-like signal. Mitigated with careful material selection, passive shielding, and fiducial cuts
Background (Muons & Neutrons): Cosmogenic & Radiogenic
We measured a muon flux of (3-4) ×10−10μ/cm2/s. 6 km.w.e. overburden drastically reduces muon flux; water Cherenkov muon veto tags remaining cosmogenic backgrounds.
PMT Borosilicate Glass (dominant neutron source)
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Background (α particles): LAr bulk Lowest Rn contamination of any noble liquid dark matter experiment! Distribution of mapped α particle energies from Fprompt and PE for short-lived α-decays in LAr.
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Leakage probabilities at energy threshold:
+1.3 )×10^-7
+0.7 )×10^-9
Strongest demonstration of PSD to date, due to low electronics noise and AP removal
Background (β and γ-rays): Electronic recoils in LAr
Probability of an electron recoil being detected above a given Fprompt value in the WIMP-search ROI. Vertical lines show the values above which 90% or 50% of nuclear recoils are expected to be found.
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After all cuts, a background expectation < 1 event was achieved At a fiducial mass of 824 kg, average WIMP efficiency is 35.4%. WIMP acceptance* as a function of PE
*Given a number of events that enter the fiducial volume, the fraction of events that survive all physics cuts is taken as the acceptance for WIMP-like recoils.
Expected backgrounds
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231 live days after run selection and deadtime corrections 0 events in ROI 824 kg fiducial mass Applying cuts to data, no WIMP candidate events are seen
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This analysis excludes spin-independent WIMP-nucleon cross-sections above 3.9×10−45 cm² @ 100 GeV WIMP mass (90% C.L.). This is a leading result for argon detectors and complementary to the results obtained from Xe-based experiments.
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3.9×10−45 cm² @ 100 GeV WIMP mass (90% C.L.).
and nuclear recoils (NRs).
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Joining the Global Argon Dark Matter Collaboration DarkSide-20k. Competitive with LZ, start operation at LNGS in 2021. Target exposure: 100 tonne·year. Future multi-hundred tonne (300) LAr detector,
exposure: 1 ktonne·year. Complimentary to xenon, the only other target allowing such large exposure.
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