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Solid State Detectors for Low-Mass Dark Matter Searches

Miriam Diamond University of Toronto Physics Dept &

Arthur B. McDonald Canadian Astroparticle Physics Research Institute

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The Dark Matter Question

So far, evidence for existence of DM comes from astrophysics

How to look for it in particle physics experiments?

2

2

you are here

~ 27%

~ 68%

+

=

?

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Come to the (Solid) Dark Side

  • What are we looking for?
  • How are we looking for it?
  • The solid program of solid-state detectors
  • SuperCDMS: apparatus, sensitivity, results with prototypes

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“What are we looking for?”

?

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“Beyond the Standard Model” Searches

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DM searches → BSM particle(s) that are:

  • Cold (non-relativistic)
  • Stable on cosmological timescales
  • Gravitationally interacting
  • Plus feeble, if any, non-gravitational interactions with each other / with luminous matter

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What mass scale?

What interactions with SM?

Are there “dark forces”?

How many new particle species?

…

Happy Valentine’s Day courtesy of Symmetry magazine

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Thermal Production of DM Particles?

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  1. DM initially in thermal equilibrium with SM, in hot “soup”
  2. Universe cools, SM no longer energetic enough to produce DM pairs, DM begins annihilating away
  3. Universe expands, DM stops annihilating (“freeze-out”)

A general, simple possibility for DM production in early universe:

time (ns)

temperature (GeV)

DM # density

Relative DM fraction

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2

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relic abundance

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WIMP Miracle?

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avg cross section

times velocity

“relic abundance”

of DM particle 𝜒

weak scale

“Weakly Interacting Massive Particles” (WIMPs)

time (ns)

temperature (GeV)

DM # density

Relative DM fraction

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2

3

relic abundance

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WIMPing out?

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But… searches where we most expected to find WIMPs haven’t found them!

Lots of WIMPy candidates:

  • Supersymmetric partners
  • Additional Higgs bosons
  • Kaluza-Klein modes
  • … etc

weak scale

arxiv.org/abs/1310.8327

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Now what?

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arxiv.org/abs/2209.07426

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My Favourite Park in the Particle Zoo

  • “Light WIMP-like DM” requires new, low-mass “dark mediators” (dark force carriers)
  • e.g. “Hidden Valley” / “Mirror Universe” models with “dark photons”
  • Look for the sub-GeV DM and also the mediators

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“Light DM”

WIMP DM

too hot

too much

CMB/BBN

  • Stick with thermal relic DM, it works (theoretically) at least down to 2me

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“How are we looking for it?”

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Search Strategies

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Complementarity between different types of experiments

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SM

SM

χ

χ

Collider

SM

SM

χ

χ

Direct

SM

SM

χ

χ

Indirect

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Search Strategies

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Complementarity between different types of experiments

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SM

SM

χ

χ

Collider

SM

SM

χ

χ

Direct

SM

SM

χ

χ

Indirect

SM

DM

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Direct Detection

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Collisions of galactic DM with SM particles in detector on Earth

v ~ 270 km/s

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Direct Detection

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DM particles collide with SM particles in detector “target” and are absorbed, or cause nuclear and/or electronic recoils

Nuclear Recoil Electron Recoil

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The GeV-Scale & Sub-GeV Detection Challenge

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Light DM (~2me) stretches traditional WIMPy direct detection techniques, which rely extensively on inelastic nuclear recoil

R. Essig

proton

mass

Not enough energy transfer

Can’t see recoil of nucleus

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The GeV-Scale & Sub-GeV Detection Challenge

For ~meV – keV dark mediators, need absorption searches

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BRN for DM Small Projects New Initiatives https://www.osti.gov/servlets/purl/1659757

proton

mass

electron

mass

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The GeV-Scale & Sub-GeV Detection Challenge

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Lowering mass and/or interaction thresholds

BRN for DM Small Projects New Initiatives https://www.osti.gov/servlets/purl/1659757

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Solid-State Detectors

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3 Channels for Next-Generation Detectors

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https://arxiv.org/abs/1509.08767

Silicon /

DM

Low thresholds

ER vs NR discrimination

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Many Next-Generation Detectors are Solid-State

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https://arxiv.org/abs/1509.08767

Silicon /

DM

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Many Next-Generation Detectors are Solid-State

Categorized by electron recoil energy (ΔE) and mDM detectable:

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(R&D) (speculative “exotic”)

…

R. Essig

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Many Next-Generation Detectors are Solid-State

Categorized by electron recoil energy (ΔE) and mDM detectable:

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(R&D) (speculative “exotic”)

…

R. Essig

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Many Next-Generation Detectors are Solid-State

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https://arxiv.org/abs/1707.04591

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Many Next-Generation Detectors are Solid-State

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https://arxiv.org/abs/1707.04591

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Underground Shielded Secret Lairs

Hide the detectors in shielding and bury them in an underground clean-room.

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Why?

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Underground Dark Shielded Lairs

Backgrounds, backgrounds, backgrounds!

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Cosmogenic

  • Cosmic ray muons
  • Spallation neutrons
  • Activated materials

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Environmental

  • Airborne radon & daughters
  • Radio-impurities in materials

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Charge-Coupled Devices (Semiconductor Pixels)

  • Take a photo of DM, like with your cellphone camera!
  • Ionization events induced by DM (instead of photons) in bulk Si of CCD pixels

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Charge-Coupled Devices (Semiconductor Pixels)

  • Pixels ~15 x 15 μm2 , hundreds of μm thick
  • “Skipper” CCDs reliably detect excitations as small as 1 electron in a pixel

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https://damic.uchicago.edu/detector.php

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Charge-Coupled Devices (Semiconductor Pixels)

  • Liquid nitrogen temperatures
  • Hour[s] of “exposure time” per “image”

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  • DAMIC (Dark Matter in CCDs)
  • SENSEI (Sub-Electron-Noise Skipper-CCD Experimental Instrument)
  • OSCURA (Observatory of Skipper CCDs Unveiling Recoiling Atoms)

DAMIC SNOLAB

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Cryogenic Semiconductor Crystals

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  • Collect phonons as well as electrons
  • Calorimetry rather than tracking/imaging
  • Operated at tens of mK

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https://arxiv.org/abs/1509.08767

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Cryogenic Semiconductor Crystals

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SuperCDMS

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Cryogenic Semiconductor Crystals

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Combination of phonon and ionization channels allows NR vs ER discrimination

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https://arxiv.org/abs/1706.01070

  • EDELWEISS (Expérience pour Detecter Les WIMPs En Site Souterrain) @ Modane
  • SuperCDMS

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Cryogenic Scintillating Crystals

Along with phonon signal: instead of collecting electrons in semiconductor crystals, collect light in scintillating crystals, operated at ~5 mK

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https://arxiv.org/abs/1904.00498

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Cryogenic Scintillating Crystals

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β/γ

NR oxygen

NR tungsten

https://arxiv.org/abs/1904.00498

Combination of phonon and light channels allows ER & gammas vs NR discrimination

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  • CRESST-III (Cryogenic Rare Event Search with Superconducting Thermometers) @LNGS

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SuperCDMS (Super Cryogenic Dark Matter Search)

Operated in a Soudan, Minnesota underground lab until 2015

More powerful version now being constructed in Canada’s world-leading astroparticle physics facility, 2 km underground in the Vale Creighton Mine near Sudbury

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SuperCDMS (Super Cryogenic Dark Matter Search)

Operated in a Soudan, Minnesota underground lab until 2015

More powerful version now being constructed in Canada’s world-leading astroparticle physics facility, 2 km underground in the Vale Creighton Mine near Sudbury

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SuperCDMS@SNOLAB

  • kg-scale Si and Ge detector modules
  • 6 modules per “tower”, 4 “towers” in cryostat

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SuperCDMS@SNOLAB

First full science run expected next year

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CUTE (Cryogenic Underground TEst) Facility @SNOLAB

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One tower now being tested in CUTE user facility

  • Calibrations
  • Detector response
  • Background measurements
  • “Early science data”!

https://arxiv.org/abs/2310.07930

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Charge Channels: High Electron Mobility Transistors

Low-noise amplifiers to read out small ionization signals

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Ge or Si

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Phonon Channels: Transition Edge Sensors + SQUIDs

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  • Phonon energy deposits cause TESs operated near critical temp to transition from superconducting to normal state
  • Signal amplification by Superconducting Quantum Interference Devices

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New in SuperCDMS: Phonon Signal Amplification

  • Drifting charges across a Vb generates cascade of “Luke phonons”
  • Lowers recoil energy threshold
  • But “true calorimetry” and NR vs ER discrimination lost

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Primary recoil energy

Luke phonon energy

Total phonon energy

Si / Ge

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SuperCDMS Detector Types

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Interleaved Z-sensitive Ionization & Phonon: both HEMTs and TESs

  • ER vs NR discrimination, especially useful for background rejection

High Voltage: only TESs

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  • lower energy threshold

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SuperCDMS@SNOLAB Sensitivity Projections

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Spin-independent nucleon-coupled DM

Neutrino fog

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Projection for setup under construction

Possible with near-term upgrades

Possible with longer-term upgrades

Already

excluded

arxiv.org/abs/2203.08463

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SuperCDMS@SNOLAB Sensitivity Projections

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Dark Photon Axion-Like Particle DM

Already

excluded

Already

excluded

arxiv.org/abs/2203.08463

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Results from Prototypes at Test Facilities are Exciting!

“HVeV”, “CPD” Si prototypes: gram-scale devices

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Results from Prototypes at Test Facilities are Exciting!

Few eV phonon resolution, can see single electron-hole pairs

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https://arxiv.org/abs/2005.14067

https://arxiv.org/abs/2204.08038

Laser calibration

Total phonon energy [eV]

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Nuclear Recoil & Electron Recoil Limits

https://arxiv.org/abs/2005.14067

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https://arxiv.org/abs/2007.14289

SuperCDMS

HVeV Run 2

Nuclear Recoil Electron Recoil

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Dark Absorption: Dark Photon & Axion-Like Limits

https://arxiv.org/abs/2005.14067

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SuperCDMS HVeV Run2

SuperCDMS

HVeV Run2

Dark Photons Axion-Like Particles

kinetic mixing

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e- coupling

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Come to the (Solid) Dark Side, We Have Cookies

  • Direct detection of WIMP-like DM at the GeV- and sub-GeV scale, through NR and/or ER, is a well-motivated challenge
  • Especially when accompanied by searches for low-mass mediators, at the eV to keV scale, through dark absorption
  • Solid-state technologies, including cryogenic semiconductor / scintillating crystals and charge-coupled devices, provide many advantages for such searches …
  • … As demonstrated in recent world-leading limits on low-mass NR, ER, dark photons, axion-like particles, …
  • Including prototype and R&D devices, promising further discovery potential in the near future

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@SuperCDMS

https://www.snolab.ca/experiment/supercdms/

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Shedding Light on Low-Energy Backgrounds

  • Low-energy background events, of unknown origin, observed in:
    • XENON1T, DarkSide-50 (liquid nobles)
    • SENSEI, DAMIC, SuperCDMS, EDELWEISS, CRESST-III (solid-state)
  • Possible explanations in solid-state detectors include:
  • Cherenkov radiation
  • Transition radiation
  • Cracking/micro-fracturing of crystals or holders
  • Luminescence & phonons from recombination

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https://arxiv.org/abs/2011.13939