Detecting Very Low Mass Dark Matter via Paleo-detectors In - - PowerPoint PPT Presentation

• Andrzej. K. DRUKIER and Maciej GORSKI

Spring 2019 adrukier@gmail.com maciej.gorski@ncbj.gov.pl

Detecting Very Low Mass Dark Matter

via Paleo-detectors

In collaboration with OKC U. Stockholm: K.Freese, S. Baum, P. Stengel

Abstract

Paleo-detectors permit to detect low-mass DM. For 5 < MDM < 15 GeV/c2 => doable!!! For 1 < MDM < 5 GeV/c2 => possible!! For 0.5 < MDM < 1 GeV/c2 => tough! For MDM < 0.5 GeV/c2 => ???? DM detection/exclusion below 5 GeV/c2 will be much more difficult than above. Most probably it will be done in Generation II searches.

An example of tracks left in solids (accelerator)

Tracks left by radioactive decays

New WIMPs Detectors

Deep bore detectors, e.g. spaghetti detectors Chemically Amplified Detectors * nano-explosives/nano-thermites * {catalase, H2O2} –system

!!! PALEO-DETECTORS (> 2000 minerals) !!!

Signatures of WIMPs interaction

1) N2 dependence of cross-section -> Stodolsky conjecture 2) (dE/dx)rn >> (dE/dx)background => Average range of recoiling nuclei M ~ 1 GeV => O(5 nm) M ~ 5 GeV => O(10 nm) M ~ 15 GeV => O(20 nm) M ~ 500 GeV => O(50 nm) M ~ 5000 GeV => O(150 nm) 3) Annual modulation 4) Particular ratio of FM = (TED/ETE) TED = Total energy deposited; ETE = Energy transferred to electrons; 5) Directional effects(??).

DM: Annual Modulation

Drukier, Freese and Spergel (1986),

Bernabei et al (2003,…,2018)

This is a 12.6 σ result

DM: Annual Modulation

BUT

Stringent limits for 15 – 500 GeV/c2, but almost no limits for M< 5 GeV/c2

Paleo-detectors may be much better

Present data for:

Halite, Gypsum, Epsomite, Olivine,Nchwaningite, Nickelbischofite

Paleo-detectors may be much better

1) Expected sensitivity limits depend on mineral. 2) At MDM < 15 GeV/c2 kinematics dominates and the Li/Be minerals are the best. 3) At MDM > 15 GeV/c2 the background is due to impurities of X(U) and X(Th), and marine evaporites seem the best. 4) In marine evaporites there is no Li/Be, but there are many borates. 5) There is no one best paleodetector, but a plurality of paleodetectors optimized for assumed MDM. 6) At low masses, dependence on mineral seems lower than at high masses. 7) Recent Monte Carlo suggests that we may reach solar neutrino floor.

Dark matter velocity distribution

Anne Green, JCAP10(2010)034 S. Chaudhury, et al. JCAP09(2010)020 (Boosted to Earth’s frame) (Not boosted to Earth’s frame)

!!! Especially important for MDM < 5 GeV/c2 !!!

Low Mass WIMPs Detection

Kinematics requires low mass targets => coherent scattering gives much more counts => current methods of background rejection fail => good spatial resolution improves S/B ratio Maximum recoil energy: MDM > 15 GeV/c2 → Erecoil ~ 1 keV C, N, O 15 > MDM > 5 GeV/c2→ Erecoil ~ 0.3 keV B, C, N, O 5 > MDM > 1 GeV/c2 → Erecoil ~ 0.1 keV Li, Be, B MDM < 1 GeV/c2 → Erecoil << 0.1 keV H, Li

Paleo-detectors

WIMPs scatter on nuclei Recoiling nuclei leads to radiation damage Etching creates tracks Tracks can be measured

MDM > 15 GeV/c2 → Erecoil ~ 1 keV AFM, X-ray, UV

15 > MDM > 5 GeV/c2 → Erecoil ~ 0.3 keV AFM, X-ray 5 > MDM > 1 GeV/c2 → Erecoil ~ 0.1 keV EM, AFM? 1> MDM → Erecoil << 0.1 keV EM

Perfect cleavage is crucial

5413 minerals

• > 2000 minerals with perfect cleavage

Can’t accept K, U, Th

• > 1500 minerals

Important groups for LM and VLM DM

• (Li,Be,B) minerals
• Graphite-like minerals ?
• Rock forming minerals
• Marine evaporite minerals

Mineralogy - all goods are here

Backgrounds in Paleo-detectors

Radioactivity :

• betas only on electrons => very low
• gammas only on electrons => very low
• alphas => challenging but rejected by length
• spontaneous fission => very low

Cosmic rays:

• depth – dependent, need > 4 km

Solar neutrinos:

• only 8B and hep for LM-DM
• also 7B and pep for VLM-DM

Major disaster possible – overlap with pp neutrinos

Signatures

Backgrounds are single peaked but peaks are broad. For monochromatic DM, N elements in a mineral => N peaks. DM halo velocity spectrum => peaks become slopes. Most rock forming minerals

• => X(U) ~ 5 ppm , X(Th) ~ 10 ppm

Marine evaporites, e.g. NaCl – => X(U) < 1 ppb, X(Th) ~ 1 ppt

Ultra low mass DM (ULM-DM) MDM < 1 GeV/c2 Very low mass DM (VLM-DM) 1< MDM < 5 GeV/c2 Low mass DM (LM-DM) 5 < MDM < 15 GeV/c2

Matching LM-DM mass with target mass

For higher energy recoils we need low mass targets Best kinematics when MDM=Mtarget For MDM< 5 GeV/c2 most of minerals are sub-optimal We measure range, not recoil energy => we need low density minerals comprising at least one low-A element. We considered following groups of speciality minerals: (Li, Be, B), graphite-like, “dirty water” There are ~ 20 borates among marine evaporites

Selection of best groups of minerals

For LM-DM analysis, figures of merit order the mineral groups as follows: Type Indication minimum density [g/cc] 1) Li 1 - 3 GeV 2.09 2) Be 3 – 5 GeV 1.81 3) B 4 – 6 GeV 1.71 4) graphite-like 5 – 8 GeV 0.87 !! 5) “dirty-water” 8 – 10 GeV 1.67 Li mineral (Zabuyelite) optimal for range from 1 to 5 GeV/c2 DM Borates are an important subset of marine evaporites i.e. minerals are very pure with very low abundance of U and Th

Favorite minerals for LM-DM

Name Formula MW density » [g/cc]

Zabuyelite Li2CO3 73.9 2.09 Bertrandite Be4Si2O7(OH)2 238.2 2.00 Barberiite (NH4)BF4 104.8 1.89 Evenkite (CH3)2(CH2)22 338.7 0.87

Microscopy.. Δx [nm] Throughput Cost Availability

Soft X 25 **** *** ** Hard X 10 *** * * AFM 1-5 *** **** **** EM 0.5 * * **

Best strategy => slice the mass range

The ability to use UV and/or X-ray microscopy is crucial. For a given mass, we maximize range using three parameters:

1) Mass of target nuclei 2) Density of target mineral 3) Velocity cutoff In paleo-detectors, very high count rate enables use of range

• cutoffs. For VLM-DM best compromise is low-A and low-density

Initially we assumed that chemical composition beats density. For MDM < 1 GeV/c2 hydrogen-containing minerals are best For MDM ~ 1 - 5 GeV/c2 Li minerals are best, For MDM ~ 10 GeV/c2 B minerals are best, For MDM ~ 15 GeV/c2 graphite-like or dirty water minerals are best.

The best for 5, 10 and 15 GeV/c2 Note that x-axis scale is different for different plots

Four-crystals experiment MDM=5 GeVc2

The analysis of track length spectra may permit to measure the DM mass for MDM > 5 GeV/c2 M

For Li minerals the LM-DM and solars decouple

Sun as the neutrino source

Solar neutrinos energy spectra

Fluxes: pp pep 8B hep

Detectability of LM - DM

ULM-DM => only Li – minerals: VLM-DM => Li – and Be - minerals LM-DM => Li -, Be – , B – and C – minerals

Readout modes:

ULM-DM => only EM and AFM VLM-DM => AFM and hard X-ray microscopy LM-DM => X-ray and UV – microscopy ULM-DM => big challenge: overlap with pep neutrinos

Comparison for low masses subtypes

Comparison for low masses subtypes Could be worse!

Comparison for low masses subtypes Could be worse!

Comparison for low masses subtypes Could be worse!

Lithium minerals

Name Formula MW density g/cc

Zabuyelite Li2CO3 73.89 2.09 Bikitaite Li2[Al2Si4O12]•2(H2O) 408.21 2.28 Bityite CaLiAl2[(AlBeSi2)O10](OH) 387.16 2.31 Hectorite Na0.3(Mg,Li)3(Si4O10)(OH)2 383.25 2.50 Borocookeite Li(1+3x)Al(4-x)[BSi3O10](OH,F)8 502.73 2.62 Griceite LiF 25.94 2.64 Cookeite LiAl4(Si3Al)O10(OH)8 522.16 2.67 Liberite Li2Be(SiO4) 114.98 2.69 Saliotite Na0.5Li0.5Al3(AlSi3O10)(OH)5 452.18 2.75 Cryolithionite Na3Li3Al2F12 371.74 2.78 Ephesite NaLiAl4Si2O10(OH)2 388.04 2.984

Thermal neutron capture in lithium

Cross section for fast neutrons interaction on Li is OK. Cross section for thermal neutrons interaction on Li is very large.

6Li + n → 3H(2.05 MeV) + 4He(2.73 MeV)

1) 6Li abundance is only 7.5% of natural Li 2) 3H don’t leave traces 3) 4He probably don’t leave traces 4) If 4He leave traces they are very long (> 10 μ) and can be very well distinguished from very short (<10 nm) recoils due to VLM-DM Aber sicher ist sicher. We also calculated Be-minerals.

Comparison for low masses subtypes Could be worse!

Comparison for low masses subtypes Stodolsky conjecture.

Resume 1

Paleo-detectors may detect DM down to 0.5 GeV/c2. At ~ 1 GeV/c2 the range requires use of E-microscopy. Zabuyelite is great for 0.5 < MDM< 5 GeV/c2 There are some Lithium minerals good for VLM-DM There are few other good minerals, e.g. Bertrandite and Borax. Multiple crystals experiment (n=2,3,4) can establish LM-DM mass.

Conclusions

Paleo-detectors permit to detect both solar neutrinos and low- mass DM. For 5 < MDM < 15 GeV/c2 => doable!!! For 1 < MDM < 5 GeV/c2 => possible!! For 0.5 < MDM < 1 GeV/c2 => tough! For MDM < 0.5 GeV/c2 => ????

We need collaborators!!! We need geologists!! We need people with best possible EM!

We have bananas, we need funds.

Backup slides

Empty bore-holes are great

Depth is crucial

Paleo-detectors

(replace Mica detectors) WIMPs scatter on nuclei Recoiling nuclei leads to radiation damage Etching creates tracks Tracks can be measured

Information is safe in paleo-detectors

Table : Annealing time at T = 300° K – Calcite 109 yrs – Olivine 1014 yrs – Tektite 1022 yrs – Zircon 1039 yrs – Diopside 10 60 yrs

Alpha source = 241Am, energy=5.486 MeV total counts 2971 Artifacts: 1 at ~3.24 MeV, 1 at 3.50 MeV

Rejection = 3*10-4 at cutoff 3.24 MeV

Four-crystals experiment Ratios of recoil length spectra (ν/DM)