the low/very low mass particle dark matter frontier
TRANSCRIPT
B.SadouletMoorea Pacific 2018.5 1 September 2018 1
The Low/Very Low Mass Particle Dark Matter Frontier
Bernard Sadoulet Dept. of Physics /LBNL UC Berkeley
UC Institute for Nuclear and Particle Astrophysics and Cosmology (INPAC)
Scope of this talk Situation September 2018 High mass region>6 GeV/c2 0.5-6 GeV/c2 intermediate mass region
G2 program. How to get to solar neutrino floor The low mass region: 1 MeV to 0.5 GeV/c2
Reachable with current technology?
The ultra low mass frontier: 1 keV-1 MeV/c2 Also 1 meV to 1 keV ultra light boson absorption
Thanks to Matt Pyle Kathryn Zurek and many colleagues but misunderstandings are mine
B.SadouletMoorea Pacific 2018.5 1 September 2018
Scope of this talkWhat do I mean by Particle Dark Matter?
We tend to speak about WIMPs: Weakly Interacting Massive Particles with mass and interaction at the weak scale, typically SUSY
=> appropriate dark matter density But lack of SUSY at LHC has obliged us to expand our exploration space!
• Theoretically: Dark Sector, Heavy or Light carriers, Dark Matter asymmetry etc.
Plenty of viable models, but much less constrained than WIMPs • Experimentally: New techniques
I would like still to speak about DM particles which act more as individual particles scattering on a target than waves!
≠ Ultra light bosons: axions, dark photons, moduli Because they are very light, long wave length, large occupation number:
best described as coherent fields =>We will hear a number of talks ot this conference
However, such bosons can be absorbed by either nuclei or electrons. Same amount of deposited energy as scattering of halo
particle of mass 106 more massive: same technology!
≠ Sterile neutrinos Different techniques: x ray detection
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B.SadouletMoorea Pacific 2018.5 1 September 2018
Basic KinematicsKinematics
Purely elastic
ultimately due to the conservation of energy and momentum. Bad news for low mass
But at low mass
Putative Dark Matter event rate goes as
Electron recoil background from Compton, betas ≈ flat at low energy Proportionally less important!
Main problem, spurious pulses, not enough redundancy to be sure of a signal
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Ed =!q 2
2mT
=m
r
2
mT
v2 1− cosθ *( ) = mχ2mT
mx +mT( )2 v2 1− cosθ *( )
where mT is the mass of the nucleon or electron
For mχ << mT , Ed ≈mχ2
mT
v2 1− cosθ *( )
1mχ
match mT to mχ as much as possible
B.SadouletMoorea Pacific 2018.5 1 September 2018
Design Drivers for Dark Matter Scattering/Absorption
Maximize potential signal Kinematics Matrix elements
Maximize sensor energy sensitivity Lower gap materials, lower temperature or Amplification
Minimize background/dark current/shot noise Radioactivity, neutrino background External influence (RF, IR, Vibration,Crystal Cracking) Gap inhomogeneity (hot spots)
Maximize discrimination Energy spectrum shape Time and pulse shape Nuclear recoil recognition (phonon/ionization or scientillation, pulse
shape) Directionality? Velocity modulation?
Maximize target mass/unit cost, leverage R&D 4
B.SadouletMoorea Pacific 2018.5 1 September 2018
Particle DM Situation in September 2018At High Mass >10GeV/c2
Nothing so far Broadly consistent with the absence of Super Sym. observation at
LHC Focus point solution in CMSSM ≈10-45 is mostly excluded
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Intermediate Mass ≈10GeV/c2
A number of closed contours, and strong limits
What is going on? See Reina’s talk
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Below 1 GeV/c2 Nearly totally open
B.SadouletMoorea Pacific 2018.5 1 September 2018
High Mass Region M>6 GeV/c2
Favored region of WIMP mechanism Noble liquids are the technologies of choice
Large target masses at reasonable cost Xe excellent self shielding, moderate Nuclear Recoil discrimination (39Ar depleted) Ar excellent Nuclear Recoil discrimination, but higher thresholds
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B.SadouletMoorea Pacific 2018.5 1 September 2018
High Mass Region M>10 GeV/c2
Complementarity of other technologies Diversity of nuclei: More general than spin independent/dependent
Velocity dependent effects (including Fermi)Haxton, Zurek Different systematics (but of course need to be in the same sensitivity
region)
Large target mass candidates Scintillators (NaI):
challenge of radioactivity but need to check DAMA See Reina’s talk
PICO Mostly for “spin dependent” Discrimination against alphas
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B.SadouletMoorea Pacific 2018.5 1 September 2018
The Intermediate Mass Region 500 MeV/c2<M<6 GeV/c2
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10’’
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Amplification MechanismsDAMIC and CRESST have currently the energy sensitivity to cover this
region, but not yet the mass But you can improve energy sensitivity by amplification. 3 incarnations
Gas multiplication Multiwire Proportional chambers, NEWS-G, Drift
Gas field induced scintillation Noble gas S2 signal
Neganov-Trofimov-Luke (NTL): CDMSLite
But lost Nuclear Recoil Discrimination 10
B.SadouletMoorea Pacific 2018.5 1 September 2018
CDMSLite Run 3 Just out of the press ArXiv 1808.09098 Neganov Trofimov Luke + Profile likelihood analysis (about factor 3 compared to Optimal Interval)
Recent Results 1: CDMSLite Run 3
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Is this believable?
B.SadouletMoorea Pacific 2018.5 1 September 2018
Recent Results 2 Dark SidearXiv 1802.06994
Decent resolution
Better job than LUX, Xe on e emission from grid
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B.SadouletMoorea Pacific 2018.5 1 September 2018
Recent Results 2 Dark Side
My main problem: assumption about behavior of the yield at low energy
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B.SadouletMoorea Pacific 2018.5 1 September 2018
Low Mass Region Projections≈2020
DAMIC/SENSEI CCD NEWS-G (Spherical Proportional Counter) Low temperature calorimeters: SuperCDMS, CRESST, Edelweiss
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SuperCDMS: Current Limits on resolution
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In principle TES r.m.s. ≈Tc3 (Pyle) Best so far 20eV baseline r.m.s. for 1.3 kg Ge 2 x our goal, <project threshold But need to control
Vibrations √ IR √ RF <= seems to be a major problem (+ correlated noise in dry fridges )
Compact TES 50µx200µ 2 10-18 W/√Hz
Distributed TES Collect over 4” 2 10-17 W/√Hz
B.SadouletMoorea Pacific 2018.5 1 September 2018
Radioactive BackgroundsTritium, 32Si
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CDMSLite Run 2 arXiv 1806.07043
B.SadouletMoorea Pacific 2018.5 1 September 2018
Low E-field Dark Current
Use of NTL amplification Need to hold voltage Delicate but our contact seem OK
However large dark current
≈ independent of field IR ? Metastable states Appears as shot noise but will give individual pulses
Maybe due to being at the surface Muons/gammas->metastable states?
Plan to test at CUTE, a new underground test facility at SNOLAB
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an early R&D detector significant improvements since
B.SadouletMoorea Pacific 2018.5 1 September 2018
Reaching The Solar Neutrino Floor
Neganov Trofimov Luke amplification mixes the primary phonons with the ionization generated phonons.
We need Nuclear Recoil discrimination in 1-6 GeV/c2 to reach solar neutrino floor
How can we restore? 1) Displacement of NR peaks
no very far for what we already measure!
2) 2 types phonon sensors One close to region where Neganov Trofimov Luke phonons are created One further away more sensitive to original phonons => Separate E0 from ENeganovTrofimovLuke some preliminary demonstration in existing detectors
3) Also progress in ionization charge amplifier (91 eV rms for 300pf detector capacitance)
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• σ=5eVt
• Singlee-/h+Sensitivity• ER/NRDiscrimination
TotalPhononEnergy[keVt]
1e-/h+ER1x(100+3)
2e-/h+ER2x(100+3)
3e-/h+ER3x(100+3)
1e-/h+NR1x(100+30)
B.SadouletMoorea Pacific 2018.5 1 September 2018
Our Low Mass DreamsEasiest:e scattering!
in condensed matter, everything is inelastic
excitations, phonons
Liquid He Lightest nucleus
HERON D. McKinsey
Can go further than naive estimates
Interesting calculations e.g., by the Zurek group of multiple excitations
e.g., back to back phonons (≠ large momentum compared to energy carried by phonons)
Penalty due to off shell process, but some sensitivity!
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US Cosmic Visions: New Ideas in Dark Matter 2017 : Community ReportarXiv:1707.04591v1
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Jeremy Mardon, SITP, Stanford
DIRECT DETECTION VS OTHER BOUNDS
10 100 1000 10410-44
10-41
10-38
10-35
10-32
10-29
mDM @MeVD
se@cm
2 D
FDMµ1êqLEP
PlanckN eff
XENON10 ER
XENON10 NR
CRESST
XQC
EDM-DM
10 100 1000 10410-42
10-40
10-38
10-36
10-34
mDM @MeVD
se@cm
2 D
FDM=1LEP
CMB
PlanckN eff
XENON10 ER
XENON10 NR
CRESST
MDM-DM
10 102 10310-4310-4210-4110-4010-3910-3810-3710-3610-35
mDM @MeVD
se@cm
2 D
FDM=1
XENON10 ER
CRESST
HeXeArGe
PlanckN eff
Massive Dark Photon
1 10 102 10310-4310-4210-4110-4010-3910-3810-3710-3610-3510-3410-3310-32
mDM @MeVD
se@cm
2 DFDM µ 1êq2
XENON10 ERHeArXeGe
Freeze-In
Ultra-light Dark Photon
e scatter:Smaller Band Gaps are better
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(Ultra-lightMediator)
Essigetal1607.01009
1kgGe~3tonofXe
https://arxiv.org/pdf/ 1108.5383.pdf
B.SadouletMoorea Pacific 2018.5 1 September 2018
SuperCDMS 1g Si deviceGo to lower crystal mass: Single e-h pair sensitivity
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B.SadouletMoorea Pacific 2018.5 1 September 2018
Dark Matter Limit at the Surface
Use only events in peaks No Background Subtraction: Optimal Interval Method
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Mean σ ! 14eV
B.SadouletMoorea Pacific 2018.5 1 September 2018
Dark Matter LimitPhys. Rev. Lett. June 2018 p121.051301
Inelastic electron recoil Dark Photon limit
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Light mediator
Heavy Mediator
As expected, factor ≈ 10-6 in mass scale
1 eV/c2!
B.SadouletMoorea Pacific 2018.5 1 September 2018
Parasitic phenomenaExcellent diagnostic tool
+ leakage current indistinguishable from dark matter
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B.SadouletMoorea Pacific 2018.5 1 September 2018
The Ultra Low Mass Frontier
How do the creative schemes proposed align to the major design drivers?
1. Maximize potential signal 2. Maximum sensor energy sensitivity 3. Minimize background/dark current/shot noise 4. Maximize discrimination 5.Maximize target mass/unit cost, leverage R&D
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B.SadouletMoorea Pacific 2018.5 1 September 2018
1. Maximize Potential Signal
Direct Coupling to Optical Phonons In many dark sector models, coupling to nuclei/electrons is through dark
photon and its small mixing with ordinary photons
Advantage of polar crystals, e.g., GaAs, Al2O3 arXiv:1712.06598v1 (Knapen, Lin, Pyle, Zurek) including coupling to L Optical phonons
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LO phonon resonant absorption needs 36 meV sensitivity
Scintillation Direct gap: Photon threshold = e threshold
Light Dark Photon mediator
LO phonon Production needs 36 meV sensitivity
Dark Photon absorption
Polar Crystal Example: Dark Photon couplings in GaAs
B.SadouletMoorea Pacific 2018.5 1 September 2018
2. Maximum Sensor SensitivityLooking for small gap
Semiconductors ≈ 1eV (scintillation in Ga As is also 1 eV) Liquid helium rotons 0.75 eV Superconductors 1 meV
Creative exuberance (cf 1985) which is refreshing Graphene and carbon nanotubes where gap can be engineered Dirac materials (Semi metal with small gaps) Spins in a magnetic field Labelled DNA (Druikier) ≈eV binding energy Color centers ≈ eV binding energy?
Need to couple to a sensitive enough sensor CCDs with skipper readout (multiple sensing) SENSEI/DAMIC but 1 eV
Low temperature sensors TES ≈Tc3
MKID Amplification mechanisms
Luke Neganov but amplifies only ionization 4He Absorption on bare surface Spin flip avalanche (cf old granules & PICO)
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B.SadouletMoorea Pacific 2018.5 1 September 2018
Promising TES result: 70 meV50µx200µ
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• Noisematchestheorytowithinx1.4– Sptot =2x10-18 W/rtHz
• !sensor ~8kHz• "E =55meV (withoutcollectionlosses
…~20%)
B.SadouletMoorea Pacific 2018.5 1 September 2018
3. Minimize Dark Count 4. Maximize Discrimination
My main worry Fabrication defect=>zero gap flooding the sensors All parasitic phenomena will show up
Can we recognize nuclear recoil? probably not below a few 100MeV
Directionality inherent in crystal asymmetries e.g., Al2O3 LO phonons (Zurek, Pyle)
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22’
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5. Target Mass and CostRate goes at 1/mDM!
We will probably see soon results with very small detectors
DAMIC/SENSEI Low Temperature Detectors R&D (e.g., SuperCDMS)
Do not underestimate cost of R&D cf. history
Thermistors used in CMB SQUIDs
Balance enthusiasm with new direction and amount needed to get in the 100g region
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B.SadouletMoorea Pacific 2018.5 1 September 2018
ConclusionsThe current combination of experiments and
technologies will cover 300 MeV/c2 to TeV/c2. “G2”: part of the way towards neutrino floor 2020-2025 G2+: go to neutrino floor
New window below 500 MeV/c2 Nuclear Recoils: Liquid He, Polar crystals Electron scattering: -> keV DM absorption:-> meV
New experimental results soon R&D for G2/G2+ paves part the way toward those ambitious goals Table top experiments
Exciting new ideas (cf 1985 era) Use/manufacture low gap systems Of course many of these clever schemes will fail, but fun
We do not need large target masses My worries
(3.) Dark Count problem (we already see in 500 MeV/c2 to 6 GeV/c2, and learn from it)
(4.) Paucity of dark matter specific signatures 34