PHY 582 Particle Physics II Experiment Lecture 8

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PHY 582 ― Particle Physics II (Experiment) Lecture 8: Dark Matter detectors Introduction: Dark

PHY 582 ― Particle Physics II (Experiment) Lecture 8: Dark Matter detectors Introduction: Dark matter WIMP detection Standard Halo model Signatures Backgrounds Classes of DM detectors Crystal Scintillator Detectors (DAMA/LIBRA, ANAIS, COSINE) m. K Detectors (CDMS, EDELWEISS, CRESST) Bubble Chambers (PICO) Noble Liquid Detectors (DEAP, XMASS, Dark. Side, LZ, XENON) Current and projected limits Arán García-Bellido PHY 582 1

Dark matter Overwhelming evidence that normal (atomic) matter is not all the matter in

Dark matter Overwhelming evidence that normal (atomic) matter is not all the matter in the Universe Properties: Gravitationally interacting Neutral, stable Not hot Not baryonic All evidence so far is from gravitational effects To identify it, we need to see it in other ways PHY 582 2

Possible candidates Theorists have come up with all kinds of candidates! Masses and interaction

Possible candidates Theorists have come up with all kinds of candidates! Masses and interaction strengths span many orders of magnitud But not all candidates are similarly motivated ar. Xiv: 1407. 0017 PHY 582 3

Relic density 1) New heavy particle X is in thermal equilibrium: XX ↔ qq

Relic density 1) New heavy particle X is in thermal equilibrium: XX ↔ qq 2) As the Universe cools: XX qq ← ∕ → 3) Universe expands: XX qq ← ∕ 1 2 → ∕ X q Bands of increasing �σAv� 3 ar. Xiv: 1003. 0904 Relation between ΩX and annihilation strength is simply: m. X~100 Ge. V, g. X~0. 6 → ΩX ~ 0. 1 Remarkable coincidence: Particle physics independently predicts PHY 582 4

WIMP detection Direct detection (LUX, CDMS, Xenon, Dark. Side, . . . ): WIMP

WIMP detection Direct detection (LUX, CDMS, Xenon, Dark. Side, . . . ): WIMP elastically scatters off nuclei → nuclear recoil Measure recoil energy spectrum in target: ionization, phonons, scintillation PHY 582 Particle colliders √s ~ few Te. V Indirect detection √s ~ 2 mχ Indirect detection (Ice. Cube, Super-K, HAWC, Fermi-LAT, CTA, . . . ): WIMPS annihilate 1) in halo: e+, p, γ or 2) in Sun: high-energy ν Colliders: missing ET, mono-jet signatures Cannot prove it’s DM Direct detection q ≤ 10 s Me. V 5

Direct detection: expected rates in detector Observable: kinetic energy of recoiling nucleus Evis ~

Direct detection: expected rates in detector Observable: kinetic energy of recoiling nucleus Evis ~ q ~ 10 s of Me. V → ER = q 2/m. N < 30 ke. V Expected rate in a detector Evi s From astrophysics: ρ0, velocity distribution f(v) [Maxwellian] From particle physics: mχ , σ Minimum velocity: v required to produce a recoil of energy ER PHY 582 6

The Standard Halo Model Local density: ρ0 = ρ(R 0) = 0. 3 Ge.

The Standard Halo Model Local density: ρ0 = ρ(R 0) = 0. 3 Ge. V/cm 3 ρ0 = 0. 008 M⊙/pc 3 = 5· 10 -25 g/cm 3 Local circular speed: vc = 220 km/s Sun’s orbital speed around center of MW Local escape speed: vesc = 544 km/s The escape speed is the speed required to escape the local gravitational field of the MW The local escape speed is estimated from the speeds of high velocity stars PHY 582 7

Signatures Expected rate: R is energy dependent due to kinematics and f(v) Test consistency

Signatures Expected rate: R is energy dependent due to kinematics and f(v) Test consistency of signal with different targets Annual Modulation: Earth annual rotation around Sun Orbital velocity has a component that is antiparallel to WIMP wind in summer and parallel to it in winter So apparent WIMP velocity (and hence R) will increase (decrease) with nd season: period of 1 year and phase t 0 ~ June 2 Small effect (few %) among other effects which also have seasonal dependence Diurnal Direction Modulation: Earth rotation about its axis, oriented at angle wrt WIMP “wind” Change the signal direction by 90° every 12 hrs. ~30% effect PHY 582 8

Backgrounds in DM detectors Radioactivity of surroundings: 238 U, 238 Th, 40 K, Ra

Backgrounds in DM detectors Radioactivity of surroundings: 238 U, 238 Th, 40 K, Ra in air Decays in rock and concrete walls of the laboratory Mostly gammas and neutrons from (α, n) and fission reactions Passive shields: Pb against the gammas, polyethylene/water against neutrons Active shields: large water Cherenkov detectors or scintillators for γ and n Radioactivity of detector and shield materials: 238 U, 238 Th, 40 K, 137 Cs, 60 Co, 39 Ar, 85 Kr, . . . Me. V neutrons can mimic WIMPs by elastically scattering from the target nuclei Ultra-pure Ge spectrometers (and other methods) are used to screen the materials before using them in a detector, down to parts-per-billion (ppb) (or lower) levels Cosmic rays and secondary reactions: need to go underground Most problematic: muons and muon-induced neutrons Hadronic component (n, p): reduced by few meter water equivalent (m w. e. ) PMT HPGe detector bkg XENON collaboration ar. Xiv: 1503. 07698 v 1 226 Ra/228 Th: PHY 582 ~1 m. Bq/PMT 9

DM experiments around the world PHY 582 10

DM experiments around the world PHY 582 10

Did you know? 1. How much radioactivity (in Bq=1 decay/sec) is in your body?

Did you know? 1. How much radioactivity (in Bq=1 decay/sec) is in your body? where from? 4000 Bq from 14 C, 4000 Bq from 40 K (e- + 400 1. 4 -Me. V γ + 8000 νe) 2. How many Radon atoms escape per 1 m 2 of ground, per s? 7000 atoms/m 2 s 3. How many plutonium atoms you find in 1 kg of soil? 10 million (transmutation of 238 U by fast cosmic ray neutrons), soil: 1 -3 mg U per kg CDMS used lead ingots from Roman sunken ships to build shileds with very low radioactivity PHY 582 11

Direct detection experiments Light: scintillating crystals, liquid noble-gas detectors Ionization/charge: directional detectors Heat: Cryogenic

Direct detection experiments Light: scintillating crystals, liquid noble-gas detectors Ionization/charge: directional detectors Heat: Cryogenic bolometers, superheated liquids DRIFT, DM-TPC, PICO, DAMIC, NEWAGE, MIMAC CDMS EDELWEISS XENON, LUX/LZ, Panda. X, Dark. Side, Ar. DM DAMA/LIBRA, COSINE, ANAIS, XMASS, DEAP PHY 582 CRESST 12

Room temperature scintillation exps DAMA-Libra, Grand Sasso; KIMS, Korea Inorganic alkali halide crystals: Na.

Room temperature scintillation exps DAMA-Libra, Grand Sasso; KIMS, Korea Inorganic alkali halide crystals: Na. I (Tl), Cs. I (Tl) High density, high light output Can be produced with high purity in large mass at affordable cost (annual modulation study) PHY 582 13

The DAMA signal 250 kg Na. I, 0. 82 tons-year → 8. 9 sigma

The DAMA signal 250 kg Na. I, 0. 82 tons-year → 8. 9 sigma Origin remains unclear, incompatible with other experiments Amplitude: ~ (0. 0116 ± 0. 0013) events/(kg ke. V d) T = 0. 999 ± 0. 001 yr, t 0 = 0. 400 ± 0. 019 (May 26± 7 days) PHY 582 14

Cryogenic experiments at m. K Detect a temperature increase after a particle interacts in

Cryogenic experiments at m. K Detect a temperature increase after a particle interacts in an absorber Principle: phonon (quanta of lattice vibrations) mediated detectors Motivation: increase the energy resolution + detect smaller energy depositions (lower the threshold) Use a variety of absorber materials (not only Ge and Si) E=deposited energy; C(T) =heat capacity of absorber; G(T) =thermal conductance of the link between the absorber and the reservoir at temperature T 0 m =absorber mass; M =molecular weight of absorber Example: at T = 10 m. K, a 1 ke. V energy deposition in a 100 g detector increases θD =Debye temperature (at which the highest frequency gets excited) the temperature by: ΔT = 1 μK→ this can be measured! PHY 582 Super. CDMS CRESST 15

Example CDMS results Calibration data: expect signal events above ionization threshold and within nuclear

Example CDMS results Calibration data: expect signal events above ionization threshold and within nuclear recoil band Two detector configurations Carve out signal timing and ionization signal PHY 582 The solid red boxes indicate the signal regions. The candidate events are the round markers inside the signal regions. The blue histograms indicate the distributions of calibration neutrons along each axis for the respective detector. 16

Cryogenic: the race for low mass WIMP Super. CDMS @ SNOLAB: Aim for 50

Cryogenic: the race for low mass WIMP Super. CDMS @ SNOLAB: Aim for 50 kg-scale experiment (cryostat can accomodate 400 kg) Focus on 1 -10 Ge. V/c² mass range Improvements: deeper lab, better materials, better shield, improved resolution, upgraded electronics, active neutron veto? 2018 -20: construction 2020: begin data taking EDELWEISS @ Modane: 2016: largest (20 kg) Ge array in operation 2017: 350 kg×d in HV mode to optimize 1 -10 Ge. V sensitivity Future: ton scale together with CDMS (EURECA) CRESST II @ LNGS: Read phonons and scintillation light from Ca. WO 4 Data taking 2013 -2015, 52 kg×d 2016: lowest thresh 300 e. Vnr PHY 582 17

PICO bubble chamber at SNOLab Chamber filled with a superheated fluid in metastable state

PICO bubble chamber at SNOLab Chamber filled with a superheated fluid in metastable state Detect expanding bubble when particle deposits energy >Eth in radius <r 0 Acoustic Discrimination Neutrons produce multiple bubbles alpha deposits energy over tens of microns NRs deposit energy over tens of nanometer Signal would appear flat in expansion time PHY 582 multiple scattering neutron event Signal would occur isotropically, bckgrounds concentrate near the walls 18

Why noble liquids for DM detection? Scalability: relatively inexpensive for large scale (multi-ton) detectors

Why noble liquids for DM detection? Scalability: relatively inexpensive for large scale (multi-ton) detectors Easy cryogenics: 170 K (LXe), 87 K (LAr) Self-shielding: very effective (especially for LXe case) for external background reduction Low threshold: high scintillation yield (similar to Na. I(Tl) but much faster timing) n-recoil discrimination: by charge-to-light ratio and pulse shape discrimination Xe nucleus (A~131): good for SI plus SD sensitivity (~50% odd isotopes) For Xe: no long-lived radioactive isotopes (Kr-85 can be removed) For Ar: radioactive Ar-39 is an issue but there are ways to overcome it mass, PHY 582 “Dark matter sensitivity scales as the problems scale as the surface area” 19

Noble gases properties PHY 582 20

Noble gases properties PHY 582 20

Dual phase liquid noble gas detector Single phase would only detect scintillation in liquid

Dual phase liquid noble gas detector Single phase would only detect scintillation in liquid Dual phase TPC: add gas to also detect ionization Single photon and electron sensitivity Z position from S 1 -S 2 timing X-Y position from S 2 signal pattern ER/NR discrimination by charge to light ratio (S 2/S 1) PHY 582 21

LZ detector: key parameters 7 ton LXe active: 5 -6 t fiducial volume, ~2

LZ detector: key parameters 7 ton LXe active: 5 -6 t fiducial volume, ~2 t skin detector Light yield >6 phe/ke. Vee, NR threshold: 6 ke. V, ER discrimination: 99. 5% Background: 1. 8 evts (8 t-yr) → Will reach 2. 5· 10 -48 cm 2 circa 2020 PHY 582 22

Sanford 4850 ft (1500 m) underground = 4300 mwe Dune LUX/LZ PHY 582 23

Sanford 4850 ft (1500 m) underground = 4300 mwe Dune LUX/LZ PHY 582 23

LZ Backgrounds Photomultipliers of ultra-low natural radioactivity Low background titanium cryostat LUX water shield

LZ Backgrounds Photomultipliers of ultra-low natural radioactivity Low background titanium cryostat LUX water shield an added gadolinium-loaded scintillator active veto Instrumented “skin” region of peripheral xenon as another veto system Radon suppression during construction, assembly and operations Ultra-low levels of Kr in Xe PHY 582 24

Example: Xenon 100 results (2009) Use calibration data: Cs-137 and Am. Be to characterize

Example: Xenon 100 results (2009) Use calibration data: Cs-137 and Am. Be to characterize electron recoil and nuclear recoil 10 observed events All compatible with expected bkg from leakage 7. 0 ± 1. 4 evts PHY 582 25

Vanilla exclusion plot Assume we have detector of mass M, taking data for a

Vanilla exclusion plot Assume we have detector of mass M, taking data for a period of time T The total exposure will be ε = M × T [kg days] Nuclear recoils are detected above an energy threshold Eth, up to a chosen energy Emax The expected number of events nexp will be: Cross sections for which nexp ≥ 1 can be probed by the experiment If ZERO events are observed, Poisson statistics implies that nexp ≤ 2. 3 at 90% CL Exclusion plot in the cross section versus mass parameter space (assuming known local density) PHY 582 26

Current limits & projections PHY 582 ar. Xiv: 1707. 06277 27

Current limits & projections PHY 582 ar. Xiv: 1707. 06277 27

The neutrino floor Neutrino-electron and neutrino-nucleus scattering 8 B neutrinos dominate: serious background if

The neutrino floor Neutrino-electron and neutrino-nucleus scattering 8 B neutrinos dominate: serious background if the WIMPnucleon cross section < 10 -10 pb Energy of nuclear recoils: <4 ke. V (heavy targets, Xe, I etc) to <30 ke. V in light targets (F, C) Non-8 B neutrinos: impact on WIMP detectors at much lower WIMP-nucleon cross sections solar Diffuse Supernova background PHY 582 atmospheric 28

Summary of direct DM searches Dark matter could be made of particles of ~100

Summary of direct DM searches Dark matter could be made of particles of ~100 Ge. V with weak couplings Dark matter models need input from astrophysics, cosmology, particle physics Lots of assumptions in Standard Halo model Direct detection requires low radioactive material backgrounds Go deep into mines/tunnels to minimize cosmic rays Several techniques employed to measure nuclear recoil: use combinations for better discrimination Cryogenic Ionization Scintillation Bubbles/acoustic Next generation of liquid noble-gas experiments of ~1 ton will push sensitivity almost to the limit of the irreducible neutrino nuclear scattering background PHY 582 29

Extras PHY 582 30

Extras PHY 582 30

Ar. DM PHY 582 31

Ar. DM PHY 582 31

Current limits PDG 2017 PHY 582 32

Current limits PDG 2017 PHY 582 32