HeRALD: Dark Matter Direct Detection with Superfluid 4He Doug - - PowerPoint PPT Presentation

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HeRALD: Dark Matter Direct Detection with Superfluid 4He Doug Pinckney on behalf of the HeRALD collaboration 10 December 2019 Phys. Rev. D 100, 092007 1 Low Mass Dark Matter Direct Detection Parameter space wide open, O(10 g-day)

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SLIDE 1

HeRALD: Dark Matter Direct Detection with Superfluid 4He

Doug Pinckney on behalf of the HeRALD collaboration 10 December 2019

1

  • Phys. Rev. D 100, 092007
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SLIDE 2

Low Mass Dark Matter Direct Detection

  • Parameter space “wide open”, O(10 g-day) exposures set leading limits
  • This space is challenging to access: for a given target mass, lower DM

mass requires lower detector threshold [O(10 eV) threshold for O(100 MeV) DM]

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103 104 105 106 107 108 109 1010 1011 1012 1013

MDM [eV/c2]

10-3 10-2 10-1 100 101 102 103 104 105 106 107

Elastic Recoil Endpoint [eV]

KEDM at cutoff

He Xe

threshold target mass

Threshold

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SLIDE 3

HeRALD: Helium Roton Apparatus for Light Dark matter

  • Superfluid 4He as a target material
  • Favorable recoil kinematics
  • Recoil energy can be fully reconstructed with TES calorimetry

from M. Pyle at UCB (top right taken from LBL RPM presentation)

  • Zero bulk radiogenic backgrounds
  • No Compton backgrounds below 20 eV
  • HERON experiment at Brown (Seidel, Maris), proof
  • f concept work

3

Superfluid 4He Calorimeters

Vacuum gap

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SLIDE 4

Excitations in Superfluid 4He

4

He

DM

Excitation

~meV Vibrations (phonons, rotons) Singlet UV (16 eV) Photons Triplet Kinetic Excitations

O(ns)

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SLIDE 5

Excitations in Superfluid 4He

5

He

DM

Excitation

~meV Vibrations (phonons, rotons) Singlet UV (16 eV) Photons Triplet Kinetic Excitations

Detection Method

Absorbed in calorimeters on 10 ns timescale

O(ns)

He* He

γ

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SLIDE 6

Excitations in Superfluid 4He

6

He

DM

Excitation

~meV Vibrations (phonons, rotons) Singlet UV (16 eV) Photons Triplet Kinetic Excitations

Detection Method

Absorbed in calorimeters on 10 ns timescale Ballistic, travel at O(1 m/s), deposit energy in immersed calorimeters

O(ns)

He* He

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SLIDE 7

Excitations in Superfluid 4He

7

He

DM

Excitation

~meV Vibrations (phonons, rotons) Singlet UV (16 eV) Photons Triplet Kinetic Excitations Adsorption of quantum evaporated He atoms on upper calorimeter + adsorption gain, 10-100 ms timescale

Detection Method

Absorbed in calorimeters on 10 ns timescale Ballistic, travel at O(1 m/s), deposit energy in immersed calorimeters

O(ns)

QP Vacuum Gap He

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SLIDE 8

Energy Partitioning

  • Nuclear and electron recoils have different energy partitioning!
  • Estimated from measured excitation/ionization/elastic scattering cross sections
  • Distinguishable with signal timing

8

Seidel

Electron excitation cutoff

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SLIDE 9

Sensitivity Projections

  • Solid red curve, 1 kg-day

@ 40 eV threshold

  • 3.5 eV (sigma)

calorimeter resolution demonstrated by Pyle at UCB

  • 9x “adhesion gain”
  • 5% quasiparticle

detection efficiency

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Neutrino Floor Direct Detection Astrophysics 1 kg-day 40 eV 100 kg-yr 1 meV

Bulk Fluid

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SLIDE 10

Activities at Berkeley (Slides from Junsong Lin)

Measure nuclear recoil (NR) scintillation light yield of superfluid helium

  • 6 one-inch PMTs monitoring one-inch cube of LHe.

  • PMTs submerged in LHe

  • Proximity leads to better light collection

  • Biased by Cockcroft-Walton (C-W) generators

  • TPB as wavelength shifter (LHe scintillation = 80 nm)

  • Demonstrated single PE sensitivity at T=1.75 K

  • Using Compton scattering to determine ER light signal yield

  • Next step: DD generator for NR light yield

λ

10

Transformer C-W Generator PMT

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SLIDE 11

Activities at Berkeley (Slides from Junsong Lin)

  • Estimate ER light signal yield

from Compton scattering peaks

  • ~0.4 PE/keVee (using 3 of 6

PMTs)

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SLIDE 12

Calibration via 24keV neutrons: Photoneutron

  • Coincidence at 24 keV:
  • Energy of convenient photoneutron source (124SbBe)
  • Energy of ‘notch’ in cross section of Fe (~25 m

interaction length)

  • Result: can surround a photoneutron source in

material opaque to gammas but transparent to 24 keV neutrons

  • Endpoint in He: 14 keV
  • 1 GBq 124 Sb source (practical) results in a few n/s

collimated neutrons

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SLIDE 13

2 −

10

1 −

10 1 10

2

10

3

10

4

10 Neutron Energy [keV] 1 10

2

10 Number of Neutrons

Neutrons and Gamma flux after the filter

Calibration via 24keV neutrons: Pulsed

  • Also looking into pulsed source based on filtered DT neutron generator

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Pb

Collimate neutrons Block gammas Filter out the 24 keV neutrons using Fe-56 moderate MeV-scale neutrons to <100 keV neutron booster, get neutrons with energy

  • f ~1 MeV using Pb n-

>2n process DT Generator (14.1 MeV, 1us timing)

Borated Poly Fe Al + AlF3 (Fluental) Pb DT 40 cm

Neutrons Gammas

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SLIDE 14

Activity at UMass

  • Characterizing dilution refrigerator
  • Uncertainty in how quasiparticles, triplet

excitations interact at surfaces

  • Achieve and enhance adhesion gain: keep

calorimeter dry, use materials with higher Van der Waals attraction

  • Adapting the HERON film burner design,

demonstrated but heat load problematic

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Condenser Surface Evaporator Surface

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SLIDE 15

Heat Load Free Film Stopping

  • Cesium coated surfaces,

demonstrated but technically difficult [Nacher and Dupont-Roc, PRL 67,

2966 (1991)] [Rutledge and Taborek, PRL 69, 937 (1992)]

  • Geometry of atomically sharp

“knife edges”, used by x-ray satellites at higher temperatures, has yet to be conclusively demonstrated [Y.

Ezoe et al J. Astron. Telesc. Instrum. Syst. 4(1) 011203 (27 October 2017)]

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Alternate Method: Nitride Overhang Anisotropically Etched Si

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SLIDE 16

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Next Steps

Data taking with optimized designs

UMass

He Film Stopping Adhesion Gain Quasiparticle Reflection

Both

keV-scale Neutron Calibration Dilution Refrigerator Characterization

Berkeley

Scintillation Yield Measurements Calorimetry Testing

  • Phys. Rev. D 100, 092007
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SLIDE 17

Extras

17

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SLIDE 18

Background Simulations

  • Radon surface backgrounds not yet considered

Thomson Delbruck Rayleigh

1 kg underground target

Neutrons

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SLIDE 19
  • PMTs are Hamamatsu R8520-06-MOD (platinum underlay for cryogenic usage)

  • PMTs and biasing system previously demonstrated to work at ~15 mK

temperature vacuum in an earlier project by Junsong & co.


  • Cockcroft-Walton (CW) generator directly generates the different individual

voltages needed by different dynode stages of the PMT. So no voltage-divider resistor circuit needed.


  • Only a few volts AC needed from room temperature, no need for high-voltage

cryogenic feedthrough

Scintillation Yield Measurement Details

19

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SLIDE 20
  • For Compton scattering, we used a 2” diameter by 2” height NaI detector as

far side detector to determine the recoil angle.

  • For DD generator, we will use a 5” diameter by 5” height BC-501A liquid

scintillator detector as far side to determine the recoil angle.

  • For both cases, coincidence is used to select true events.
  • Currently, I only understand the single PE area from 3 of the 6 PMTs well to

sum up their area

More Scintillation Yield Measurement Details

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SLIDE 21

Helium Compton Scattering

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SLIDE 22

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From Scott Hertel

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SLIDE 23

23

Evaporator Surface Condenser Surface Condenser Surface Experimental film stoppage area

Film Burner Model

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SLIDE 24

Excitations in Superfluid 4He

24

He

DM

Vibrations (phonons, rotons) Excitations Ionization

Detected State

Vibrations (phonons, rotons) Dimer Excimers (IR Photons) Singlet UV Photons Triplet Kinetic Excitations

He+ e- He* He* He

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SLIDE 25

Sensitivity Projections Cont.

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Curve Exposure Threshold Solid Red 1 kg-day 40 eV Dashed Red 1 kg-yr 10 eV Dotted Red 10 kg-yr 0.1 eV Dashed-Dotted Red 100 kg-yr 1 meV Dashed- Dotted-Dotted Red 100 kg-yr 1 meV

+ off shell phonon sensitivity Neutrino Floor

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SLIDE 26

Extending Sensitivity with Off Shell Interactions

  • The 0.6 meV evaporation threshold limits

nuclear recoil DM search to mDM >~ 1 MeV

  • Can be avoided if we find an excitation

with an effective mass closer to the DM mass, allow DM to deposit more energy in the detector

  • In helium this could be recoiling off the

bulk fluid and creating off shell quasiparticles

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SLIDE 27

Detecting Vibrations: Vibrations in Helium

  • The vibrational (“quasiparticle”, “QP”)

excitations we expect to see are phonons and rotons

  • Velocity is slope of dispersion relation
  • Rotons ~ “high momentum phonons”
  • Just another part of the same

dispersion relation

  • R- propagates in opposite direction to

momentum vector

27

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SLIDE 28

Example Waveform

  • Based on HERON R&D
  • Can distinguish scintillation and

evaporation based on timing

28

  • J. S. Adams et al. AIP Conference Proceedings 533, 112 (2000)

Annotations from Vetri Velan 365 keV electron recoil

HERON DATA

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SLIDE 29

Another Example Waveform

  • Distinguish between different phonon distributions by arrival time in detector
  • R+ arrive first
  • P travel at a mix of slower speeds and arrive next
  • R- can’t evaporate directly, need reflection on bottom to convert into R+ or P

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p0 p1 p2 Recent Quasiparticle Simulation R+ P R-

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SLIDE 30

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SLIDE 31

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