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 < M DM < 15 GeV/c 2 => doable!!! For 1 < M DM < 5 GeV/c 2 => possible!! For 0.5 < M DM < 1 GeV/c 2 => tough! For M DM < 0.5 GeV/c 2 => ???? DM detection/exclusion below 5 GeV/c 2 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, H 2 O 2 } –system !!! PALEO-DETECTORS (> 2000 minerals) !!!
Signatures of WIMPs interaction N 2 dependence of cross-section -> Stodolsky conjecture 1) 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),
DM: Annual Modulation Bernabei et al (2003,…,2018) This is a 12.6 σ result
BUT Stringent limits for 15 – 500 GeV/c 2 , but almost no limits for M< 5 GeV/c 2
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 M DM < 15 GeV/c 2 kinematics dominates and the Li/Be minerals are the best. 3) At M DM > 15 GeV/c 2 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 M DM . 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 M DM < 5 GeV/c 2 !!!
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: M DM > 15 GeV/c 2 → E recoil ~ 1 keV C, N, O 15 > M DM > 5 GeV/c 2 → E recoil ~ 0.3 keV B, C, N, O 5 > M DM > 1 GeV/c 2 → E recoil ~ 0.1 keV Li, Be, B M DM < 1 GeV/c 2 → E recoil << 0.1 keV H, Li
Paleo-detectors WIMPs scatter on nuclei Recoiling nuclei leads to radiation damage Etching creates tracks Tracks can be measured M DM > 15 GeV/c 2 → E recoil ~ 1 keV AFM, X-ray, UV 15 > M DM > 5 GeV/c 2 → E recoil ~ 0.3 keV AFM, X-ray 5 > M DM > 1 GeV/c 2 → E recoil ~ 0.1 keV EM, AFM? 1> M DM → E recoil << 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 8 B and hep for LM-DM - also 7 B 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 – M DM < 1 GeV/c 2 Ultra low mass DM (ULM-DM) 1< M DM < 5 GeV/c 2 Very low mass DM (VLM-DM) 5 < M DM < 15 GeV/c 2 Low mass DM (LM-DM)
Matching LM-DM mass with target mass For higher energy recoils we need low mass targets Best kinematics when M DM =M target For M DM < 5 GeV/c 2 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/c 2 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 M W density » [g/cc] Zabuyelite Li 2 CO 3 73.9 2.09 Bertrandite Be 4 Si 2 O 7 (OH) 2 238.2 2.00 Barberiite (NH 4 )BF 4 104.8 1.89 Evenkite (CH 3 ) 2 (CH 2 ) 22 338.7 0.87 Microscopy.. Δ x [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 M DM < 1 GeV/c 2 hydrogen-containing minerals are best For M DM ~ 1 - 5 GeV/c 2 Li minerals are best, For M DM ~ 10 GeV/c 2 B minerals are best, For M DM ~ 15 GeV/c 2 graphite-like or dirty water minerals are best.
The best for 5, 10 and 15 GeV/c 2 Note that x-axis scale is different for different plots
Four-crystals experiment M DM =5 GeVc 2
The analysis of track length spectra may permit to measure the DM mass for M DM > 5 GeV/c 2 M
For Li minerals the LM-DM and solars decouple
Sun as the neutrino source
Solar neutrinos energy spectra Fluxes: pp pep 8 B 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 M W density g/cc Zabuyelite Li 2 CO 3 73.89 2.09 Bikitaite Li 2 [Al 2 Si 4 O 12 ]•2(H 2 O) 408.21 2.28 Bityite CaLiAl 2 [(AlBeSi 2 )O 10 ](OH) 387.16 2.31 Hectorite Na 0.3 (Mg,Li) 3 (Si 4 O 10 )(OH) 2 383.25 2.50 Borocookeite Li (1+3x) Al (4-x )[BSi 3 O 10 ](OH,F) 8 502.73 2.62 Griceite LiF 25.94 2.64 Cookeite LiAl 4 (Si 3 Al)O 10 (OH) 8 522.16 2.67 Liberite Li 2 Be(SiO 4 ) 114.98 2.69 Saliotite Na 0.5 Li 0.5 Al 3 (AlSi 3 O 10 )(OH) 5 452.18 2.75 Cryolithionite Na 3 Li 3 Al 2 F 12 371.74 2.78 Ephesite NaLiAl 4 Si 2 O 10 (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. 6 Li + n → 3 H(2.05 MeV) + 4 He(2.73 MeV) 1) 6 Li abundance is only 7.5% of natural Li 2) 3 H don’t leave traces 3) 4 He probably don’t leave traces 4) If 4 He 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/c 2 . At ~ 1 GeV/c 2 the range requires use of E-microscopy. Zabuyelite is great for 0.5 < M DM < 5 GeV/c 2 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.
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