Dark Maer: New Technologies

Daniel McKinsey LUX Co-Spokesperson UC Berkeley and LBNL

TAUP 2017 Sudbury, Canada July 26, 2017 S

7/26/17 D. McKinsey New DM Technologies 1 Current State of the Field

7/25/17 D. McKinsey New DM Technologies 2 Current State of the Field

More mass (LXe, LAr)

7/25/17 D. McKinsey New DM Technologies 3 Current State of the Field

Lower threshold Lighter targets

More mass (LXe, LAr)

7/25/17 D. McKinsey New DM Technologies 4 There’s plenty of room at the boom

See Tracy Slatyer’s plenary talk for physics movaon for light dark maer (thermal, asymmetric, freeze-in, SIMP, ELDER…)

7/25/17 D. McKinsey New DM Technologies 5 There’s plenty of room at the boom

Non-trivial requirements: • low thresholds • control of radioactive backgrounds • control of dark counts & instrumental backgrounds 7/25/17 D. McKinsey New DM Technologies 6 US Cosmic Visions: New Ideas in Dark Maer

• Many of the technologies discussed here were compiled in the Cosmic Visions Dark Maer effort in the US, driven by the DOE Office of High Energy Physics. • Invesgang low-cost & high-impact opportunies in Dark Maer (DM) science – The G2 experiments (ADMX, LZ, and SuperCDMS) are flagships of the US Dark Maer program and obvious priority – “New Ideas in Dark Maer” workshop focused on complementary science that can be done by small projects <$10M (some much less) – 100+ talks in 4 working groups, presenng new ideas, proposals, and science and R&D results • See hps://indico.fnal.gov/conferenceDisplay.py?confId=13702 • See arXiv:1707.04591 • A few of the ideas for direct detecon described in this talk.

7/26/17 D. McKinsey New DM Technologies 7 sub-GeV DM

Disnguish two types of interacons, e.g.

σe vs mDM σN vs mDM

• dark photon mediator • dark photon mediator • vector, coupling • vector, coupling predominantly to leptons predominantly to quarks • scalar

Important to test interacons separately Benchmarks: dark-photon mediators “Heavy” Ultralight

excing complementarity ultralight mediator scenario with collider & beam-dump is uniquely probed by probes (for elasc scaering) Direct Detecon Absorpon

Si or Ge detector

superconductor long-term R&D Direct Detecon Summary Slide from Cosmic Visions

Explore hidden-sector targets: Electron recoil (ER) • ER Projects ready now explore elasc scalar thermal relic, asymmetric, SIMP/ Elder, freeze-in • R&D needed to push to weaker couplings & MeV-mass NR • Long-term R&D to reach keV masses

Opportunies to explore WIMP-p SD scaering also ready now

Nuclear recoil (NR) Spin independent 11 Nigel Smith (WIMPs) Gianpaolo Carosi (Axions) This talk XENON ADMX LXe bubble chamber LUX/LZ HAYSTAC Water bubble chamber DEAP CAPP Haloscope (CULTASK?) Direconal gaseous TPC (CYGNUS) DarkSide-50/-20k ORGAN Graphene (PTOLEMY G3) CDEX Orpheus Internally amplified Ge Edelweiss MADMAX Xenon charge-only CRESST QUAX Scinllang crystals (GaAs, NaI) SuperCDMS LC-Circuit Color centers PICO ABRACADABRA Superfluid helium with TES readout DAMIC/SENSEI CASPEr Superfluid helium with ionizaon NEWS-G DRIFT

This is not a fully exhausve list; apologies if your favorite technology is not covered!

7/26/17 D. McKinsey New DM Technologies 12 Low Mass Dark Maer: The Wild West of Direct Detecon

7/25/17 D. McKinsey New DM Technologies 13 Low Mass Dark Maer: The Wild West of Direct Detecon

Small homesteads, wide open (parameter) spaces 7/25/17 D. McKinsey New DM Technologies 14 Backgrounds for sub-GeV

• Solar neutrino background is small • Radiogenic backgrounds to few-eV electron recoil events likely <1 event/ kg/year/eV (based on projecons for measured values at O(50 eV)) • For sub-GeV searches, crical backgrounds are: • dark counts • EM interference • vibraons

7/25/17 D. McKinsey New DM Technologies 15 Scinllang Xenon Bubble Chamber Prototype (Northwestern University) Muon paddle Bubble Chamber Camera Vacuum Cryostat • Concept: Coincident scinllaon IR illumina@on PMT and bubble nucleaon by nuclear recoils –65 to –50 °C 43 – Extreme electron recoil discriminaon as in freon superheated bubble chambers

Mirrors – Event-by-event energy Scin@lla@on & from scinllaon signal Piezo Bubble – Now demonstrated in –105 °C liquid xenon LXe

arXiv:1702.08861 normal [PRL 118, 231301] To hydraulic controller

TAUP - July 26, 2017 16 Scinllang 2 1

Bubble Chamber 0 • Potenal for sub-keV −1 LED Gate Image shown at left −150 −100 −50 0 50 Time from DAQ trigger (ms) thresholds and light nuclei 2 1 1 [PMT pulse area (au)] (Ar, Ne, …) 10 Acoustic amplitude (au) – Beer low-threshold 0 0 log −1 LED Gate Image shown at left −1 electron discriminaon than −150 −100 −50 0 50 Time from DAQ trigger (ms) −0.5 0 0.5 1 1.5 freon chambers Time from acoustic t0 (ms) 1 200 [PMT pulse area (au)] 10

– Acoustic amplitude (au) 0 Low-energy NR calibraons 0 150 log underway 100 Acousc Signal −1 −10 −0.5 50 0 0.5 1 1.5 • CEnNS physics in reach at Time from acoustic t0 (ms) PMT amp (mV) −20 200 −250 −200 −150 −100 −50 0 −50 0 50 100 150 200 Xenon pressure (psia) Time from DAQ trigger (s) Time from PMT trigger (ns) O(10) kg scale 150 0 • Unique 1100 –10 GeV/c2 WIMP −10 50 Scinllaon Signal PMT amp (mV) −20 sensivity at ton-scale −250 −200 −150 −100 −50 0 −50 0 50 100 150 200 Xenon pressure (psia) Time from DAQ trigger (s) Time from PMT trigger (ns)

TAUP - July 26, 2017 17 Water as a Bubble Chamber (M. Szydagis, U Albany) • Water does not naturally scinllate. BUT: – Can look at Cerenkov light from high energy interacons as ER veto – Beer yet, can dope water with quantum dots, some of which can have triple the light yield of LXe

• Natural advantages of using H2O – Cheap, non-cryogenic, and easy to purify; has lots of protons (sub-GeV DM target). – Can be passed through hydrophilic nano-pore membrane, new tech for any bubble chamber (or a TPC)! CYGNUS HD10, a 10 m3 gas me projecon chamber

Gas mixture: SF6:4He, p ~ 1 atm. • Possibility of switching from atmospheric pressure (search mode) operaon to low pressure operaon for (improved) direconal confirmaon of WIMP signal. • Reduced diffusion via negave Ion dri (SF6)

Charge amplificaon via Micromegas

HD – high resoluon charge readout via x/y strips (200 μm pitch) for improved • 3D direconality with head-tail sensivity • Electron event rejecon • Fiducializaon

Redundant 3D fiducializaon • SF6 minority carriers • Charge cloud profile

Helium target • Improved sensivity to low mass WIMP • Longer recoil tracks, extending electron event discriminaon to lower energies through Helium target

7/25/17 D. McKinsey New DM Technologies 19 PTOLEMY-G3 Detector: Graphene field-effect transistors (G-FETs) arranged into a fiducialized volume of stacked planar arrays – Graphene cube (G3), with mass 1kg ~ 1010 cm2 ~ 109 cm3

Will look for MeV dark maer scaering events that liberate an electron from a graphene target, in the absence of any other acvity in the G3

See Y. Hochberg, Y. Kahn, M. Lisan, C. Tully, K. Zurek, arXiv:1606.08849

G-FET sensor element (Graphene Nanoribbon Array) FET-to-FET hopping trajectory

z

y x

7/26/17 D. McKinsey New DM Technologies 20 Fiducialized Volume (G3)

G-FET sensor element FET-to-FET hopping trajectory

z

y x

20 Graphene Nanoribbon Array (produced Stacked planar arrays of G-FETs at ) 1kg ~ 1010cm2 ~ 109cm3 Resistance-Temperature (RT) and Current- Cryogenically cooled (4.2K) Voltage (IV) curves in progress Cryopumping of gas contaminants on G3 Scalability to interdigitated capacitor with surface from line-of-sight trajectories pixel areas of 1mm2 or larger Low mass substrates with ALD dielectric

produce a total cold mass lighter than one 21 LHC magnet

Germanium Detectors with Internal Amplificaon (Dongming Mei, U South Dakota) This experiment would use an ionizaon amplificaon technology for Ge in which very large localized E-fields are used to accelerate ionized excitaons produced by parcle interacon to kinec energies larger than the Ge bandgap, at which point they can create addional electron-hole pairs, producing intrinsic amplificaon.

This amplified charge signal could then be read out with standard high-impedance JFET- or HEMT-based charge amplifiers.

Such a system would potenally be sensive to single ionized excitaons produced by DM interacons with both nuclei and electrons. In addion, purposeful doping of the Ge could lower the ionizaon threshold by a factor of 10, to ~ 100 meV, making the detector sensive to 100 keV DM via electron recoils. 7/26/17 D. McKinsey New DM Technologies 22 Few-electron detecon with two-phase Xe detectors (P. Sorensen, A. Bernstein)

Idea: Deploy a small O(10) kg liquid xenon TPC with a focus on electron counng and Prototype migaon of e- backgrounds. at LLNL

Ways to reduce electron backgrounds:

1) Larger electron emission field – XENON achieved ~5.5 kV/cm – Suspect >7 kV/cm needed for substanal reducon of e-train bkgd

2)Infrared photons to liberate trapped e- – Liquid surface trapping potenal is 0.34 eV – 940 nm LEDs readily available (1.3 eV photon), trigger on S2

3) Last resort: HV switching – Divert trapped electrons back to gate electrode – Possible in principle, may actually work quite well

7/26/17 D. McKinsey New DM Technologies 23 Scinllators with transion edge sensor readout Sensivity to dark maer – electron interacons. No E field = No dark current Philosophy: Running in equilibrium, use TES detecon efficiency and photon energy resoluon to minimize dark counts.

GaAs: Derenzo et al: 1607.01009

Pure NaI, CsI: J. Liu 83 photons/keV seen at 77K

No aerglow seen in GaAs

7/26/17 D. McKinsey New DM Technologies 24 Scinllators with transion edge sensor readout

Or, choose your favorite scinllator No E field = No dark current (LXe, CaWO4, …)

Maximize light yield and target mass, minimize band gap, aerglow, and background.

No aerglow seen in GaAs

7/26/17 D. McKinsey New DM Technologies 25 Color centers (R. Budnik and collaborators)

7/26/17 D. McKinsey New DM Technologies 26 Why Superfluid Helium?

Light baryonic target with mulple signal channels, including light, charge, triplet excimers, phonons, and rotons. (W. Guo and D. N. McKinsey, PRD 87, 115001 (2013).

7/25/17 D. McKinsey New DM Technologies 27 Superfluid helium-4 as a detector material

• Search for the electric dipole Measurement of neutron lifetime: moment: R. Golub and S.K. Lamoreaux, P.R. Huffman et al, Nature 403, 62-64 (2000). Phys. Rep. 237, 1-62 (1994).

7/25/17 D. McKinsey New DM Technologies 28 Superfluid helium-4 as a detector material

Proposed for measurement of pp solar neutrino flux using roton detection (HERON): R.E. Lanou, H.J. Maris, and G.M. Seidel, Phys. Rev. Lett. 58, 2498 (1987).

Two signal channels, heat and light. Both measured with a bolometer array.

Also, “HERON as a detector?” in “Dark Matter, Quantum Measurement” ed Tran Thanh Van, Editions Frontieres, Gif-sur-Yvette (1996)

7/25/17 D. McKinsey New DM Technologies 29 Why Superfluid Helium-4? • Liquid down to 0 K, allowing 10-100 mK-scale TES readout. – Take advantage of the great advances in TES technology – Take advantage of possible ~ 100% detecon efficiency for photons, triplet excimers – Take advantage of the extremely low vapor pressure of superfluid helium at low temperatures, enabling quantum evaporaon-based heat signal amplificaon. • Helium is expected to have robust electronic excitaon producon efficiency, with a forgiving Lindhard factor, so nuclear recoil scinllaon signals should be relavely large. • Negligible target cost • Low nuclear mass and charge -> low backgrounds from neutrino-nucleus scaering and gamma-nucleus scaering. • Low vibraon sensivity: As a superfluid, small velocies don’t generate excitaons. • Large ionizaon gap -> less signal quanta per keV than in super-, semiconductors. But no electron recoil background below 16 eV. • Impuries easily removed from helium using cold traps and geers, and will literally fall out of the superfluid. 7/25/17 D. McKinsey New DM Technologies 30 Reading Out Singlet Excitaons (16 eV Photons)

Detecng photons is a simple calorimetry applicaon. Operang calorimetry in LHe: less Simple detector: box standard. Possible thanks to: with calorimetry inside - Huge LHe-solid Kapitza resistance - Fast conversion of photon energy to non-phonon excitaons (e.g. Al quasiparcles)

Triplet excimers may also be read out using the same calorimetry!

F. Carter et al, J Low Temp Phys (2016) arXiv:1605.00694

7/25/17 D. McKinsey New DM Technologies 31 Phonons and Rotons

Superfluid supports vibraonal modes (some non-intuive).

Ballisc, ~150 m/s.

Enormous Kapitza resistance, i.e. ny probability of crossing into solid.

Few downconversion pathways.

Most signal expected in R- and R+ rotons, with absorpon probability measured to be 2.8 x 10-3. See Brown and Wya, J. Phys.: Condens. Maer 15, 4717 (2003).

7/25/17 D. McKinsey New DM Technologies 32 Phonons and rotons can change type when reflecng from surfaces

Calculaons based on Tanatarov et al., arXiv:1004.3497

refection mode-change probabilities upper three: solid interface (blue=0, red=1) lower three: vacuum interface R [i −> 1] R [i −> 2] R [i −> 3]

1.5 1.5 1.5

1 1 1 i i i Θ Θ Θ

0.5 0.5 0.5

0 0 0 0 1000 2000 R [i −3000> 1] 4000 5000 0 1000 2000 R [i −3000> 2] 4000 5000 0 1000 2000R [i −3000> 3] 4000 5000 p [eV/c] p [eV/c] p [eV/c] 1.5 1.5 1.5

1 1 1 i i i Θ Θ Θ

0.5 0.5 0.5

0 0 0 7/25/17 0 1000 2000 3000 4000 5000 D. McKinsey New DM Technologies 0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 33 5000 p [eV/c] p [eV/c] p [eV/c] Quantum evaporaon from superfluid helium – vacuum interface

Heat amplificaon from desorpon – adsorpon process Adsorpon gives 10-40 meV depending on surface

7/25/17 D. McKinsey New DM Technologies 34 Reading out 4He Quasiparcles (Quantum Evaporaon) Substanal amplificaon of heat signal through quantum evaporaon, followed by helium atom adsorpon

7/25/17 D. McKinsey New DM Technologies 35 Athermal Evaporaon – Demonstrated by HERON R&D

7/25/17 D. McKinsey New DM Technologies 36 Superfluid Helium Detector Concept

Signal channels: 1) Scinllaon 2) Ballisc Triplet Excimers 3) Phonons/Rotons

No dri field, and no S2 signal • No worry of few-electron background • Posion reconstrucon via signal hit paerns • (Though could apply dri field to detect single electrons via roton/phonon producon.)

Best for energies down to 300 eV.

Discriminaon using signal raos

Posion reconstrucon using signal hit paerns

7/25/17 D. McKinsey New DM Technologies 37 Electron recoil / nuclear recoil discriminaon

Toy Monte Carlo detecon efficiencies: - singlet UV photons: 0.95 (4pi coverage by calorimetry) - Triplet excimers: 5/6 (only solid surfaces) - IR photons: 0.95 (similar to UV photons)

Excellent predicted discriminaon at sub-keV energies

7/25/17 D. McKinsey New DM Technologies 38 Heat-only Readout?

Signal channels: Phonons Rotons

Energies down to ~ few meV !!

Discriminaon using roton/phonon signal raos likely. Electron recoils, detector effects, nuclear recoils likely create different roton/ phonon distribuons.

Posion reconstrucon using signal hit paerns

7/25/17 D. McKinsey New DM Technologies 39 Projected sensivity to keV-scale dark maer parcles

K. Schutz and K. Zurek, Phys. Rev. Le. 117, 121302 (2016) and S. Knapen, T. Lin, and K. Zurek, arXiv:1611.06228.

Instead of coupling to a single nucleus, couple to virtual mode in the superfluid helium, which in turn decays to mul-excitaons

Producon of mul-excitaons allows high energy transfer from the low-mass, low-momentum dark maer parcle

7/25/17 D. McKinsey New DM Technologies 40 Expected Backgrounds

Backgrounds included: - Neutrino nuclear coherent scaering - Gamma-ray electron recoil backgrounds (similar to SuperCDMS) - Note: Helium itself is naturally radiopure, and easily purified of contaminants - Gamma-ray nuclear recoil backgrounds (see Robinson, PRD 95, 021301 (2017)

Arguments for low “detector” backgrounds: - Low-mass calorimeter, easy to hold - Target mass highly isolated from environment (superfluid: fricon-free interfaces)

7/25/17 D. McKinsey New DM Technologies 41 Projected Sensivity Inial sensivity studies, taking neutrino and gamma ray backgrounds into account: (with S. Hertel, UCB/LBL -> U. Massachuses, Amherst Junsong Lin, Andreas Biekert, Vetri Velan, UC Berkeley)

7/25/17 D. McKinsey New DM Technologies 42 Projected Sensivity

Even a small mass (~ kg) of superfluid helium can probe substanal dark maer parameter space

7/25/17 D. McKinsey New DM Technologies 43 Projected Sensivity Larger target mass (~ 100 kg) of superfluid helium, with lower energy threshold (~ 10 meV) can push even lower in dark maer Superfluid He w/ ultra-low threshold mass and cross-secon

7/25/17 D. McKinsey New DM Technologies 44 Superfluid helium readout via field ionizaon (See arXiv:1706.00117) Goal: an even more sensive way to detect He atoms produced through quantum evaporaon, reaching energy sensivity of 1 meV

1 U = ↵ E~ 2 int 2 | |

A) Direct impact B) Orbital capture The polarizaon force draws helium to the C) Surface diffusion p, where the field gradient is highest. D) Bouncing

7/25/17 D. McKinsey New DM Technologies 45 Superfluid helium readout via field ionizaon (See arXiv:1706.00117) Field ionizaon detector array

DM parcle

Rotons and phonons

Recoil helium atom

Liquid helium

7/25/17 D. McKinsey New DM Technologies 46 Summary and Outlook

Rising theorecal interest in low-mass dark maer

Lots of open parameter space, can be probed by small (inexpensive) experiments

Many proposed approaches, which is appropriate as the field discovers which approaches work and which do not.

Much lower energy thresholds will bring new technical challenges, primarily instrumental backgrounds.

Expect rapid development in this area!

7/25/17 D. McKinsey New DM Technologies 47 Backup

7/25/17 D. McKinsey New DM Technologies 48 Helium-4 Nuclei: A Natural Match for Light Dark Maer Detecon

Another view: maximum recoil energy for various targets, as a funcon of WIMP mass.

7/25/17 D. McKinsey New DM Technologies 49 Why Superfluid Helium for Low-mass Dark Maer Detecon? (W. Guo and D. N. McKinsey, PRD 87, 115001 (2013).

• Kinemac matching with light dark maer candidates. – Pull the energy deposions up in energy, to above threshold. – Gain access to more of the WIMP velocity distribuon, for a given energy threshold.

• Superfluid helium offers mulple signals to choose from, and to separate dark maer signal from backgrounds (both electron recoils and detector backgrounds). – Prompt light – Delayed triplet excimers – Charge – Heat (roton and photon quasiparcles)

7/25/17 D. McKinsey New DM Technologies 50 Liquid helium-4 predicted response (Guo and McKinsey, arXiv:1302.0534, Phys. Rev. D 87, 115001 (2013).)

Liquid helium has lower electron scinllaon yield for electron recoils (19 photons/keVee)

But, extremely high Leff, good charge/light discriminaon and low nuclear mass for excellent predicted light WIMP sensivity

Calculated nuclear recoil signals Measurements in literature!

7/25/17 D. McKinsey New DM Technologies 51 Predicted nuclear recoil discriminaon and signal strengths in liquid helium

for He decreases to about 0.4 at low energies, due to Lindhard effect, but is not equal to the Lindhard factor ! 7/25/17 D. McKinsey New DM Technologies 52 Underway: Development of a NR light yield measurement

Scaer fast in LHe to measure light yield (as we have done previously in LXe, LAr, and LNe). This is yet to be measured in LHe!

Neutron sources available:

➢ DD neutron generator ○ 2.8 MeV and 106 n/s ➢ 88Y-Be photoneutron ○ 153 keV and ~103 n/s ➢ 124Sb-Be photoneutron ○ 24 keV and ~103 n/s

53 How to detect triplet helium molecules? New demonstraon: Transion Edge Sensor operated immersed in superfluid helium See F. Carter et al, arXiv:1605.00694

The collecon area here is just Coincidence: prompt singlet photon the transion edge sensor itself Microscopic. One (max) Non-coincidence: delayed triplet molecule excitaon per recoil. (+untagged photons)

7/25/17 D. McKinsey New DM Technologies 54 Phonon/roton reflecvies have complex energy and angular dependence

Tanatarov et al, arXiv:1004.3497v1

7/25/17 D. McKinsey New DM Technologies 55 A mirrored box for heat collecon

Analogy with light detectors, which collect scinllaon light from a crystal or scinllang liquid, using a reflector around the scinllator to efficiently steer the light into a photomulplier.

Here is a standard NaI detector, this one from Ortec:

7/25/17 D. McKinsey New DM Technologies 56 Discriminaon based on electronic excitaon/heat rao:

G. Seidel:

S. Hertel:

7/25/17 D. McKinsey New DM Technologies 57 Discriminaon without electronic excitaons?

For very low energies, electronic excitaons are heavily suppressed. Need to move to a scheme that doesn’t rely on electronic excitaons, only heat.

How to get parcle idenficaon without electronic excitaons?

Possibly could look at roton/phonon rao, or more generally the momentum distribuon of the quasiparcles. Given that ER and NR have different dE/dx, it’s quite plausible that they give different quasiparcle distribuons. Higher dE/dx should result in a more thermalized (colder) quasiparcle distribuon.

7/25/17 D. McKinsey New DM Technologies 58 Projected sensivity to keV-scale dark maer parcles

7/25/17 D. McKinsey New DM Technologies 59 Liquid helium cryostat at UC Berkeley

➢ Cools down to ~1.5 K ○ 4He is superfluid below ~ 2.1 K ○ 4He scinllaon normal versus superfluid

60 Light detecon with PMTs, operang in superfluid helium

➢ Pt underlay to avoid posive charge accumulated in cathode

➢ Demonstrated to work at milli-Kelvin temperature

➢ Pt underlay decreases QE ○ 16% with Pt versus 30% in XENON100

61 Helium cell design

➢ Mechanical mounng for the panel with TPB deposited

➢ A cube has 8 verces, 6 panels × 2 = 12. ○ 8 < 12. Cannot use diagonal. Off-diagonal design.

➢ Thickness of panels ○ 0.5 mm in PMTs in helium scenario ○ 2 mm in PMTs in vacuum scenarios

62 How low of an energy can be probed?

Electron recoil Nuclear recoil (excited by electron) (excited by neutron)

Light yield (photons/keV) 22 9 @ ~1 keVnr (predicted prompt secon, Ito 2013)

TPB conversion efficiency 1.35

Light collecon efficiency 0.5

PMT quantum efficiency 0.14

Photoelectrons/keV 2.1 0.85

Aim for a few keVnr with this setup. The next experiment will use transion edge sensor readout at < 100 mK temperatures, with ~ 100% quantum efficiency.

63 Simulaons PMTs in liquid helium (submerged) or in vacuum ○ Submerged scenario: More dead helium, thinner acrylic panel ○ Vacuum scenario: Less dead helium, thicker acrylic panel

• No big difference in recoil spectrum • Technically easier to implement design with PMTs submerged in liquid helium.

64