Jianglai Liu Shanghai Jiao Tong University

EPS 2017, Lido Island, July 6-11, 2017 1 Composition of the universe

Dark energy 68.3% 26.8%

4.9% Ordinary matter 2 Galactic halo

. DM local density around us: 0.32(0.02)* GeV/cm3 *inclusion of new LAMOST survey data, arXiv:1604.01216 . The solar system is cycling the center of galaxy with on average 220 km/s speed (annual modulation in earth movement)

3 WIMP, the miracle, and detectability

BSM new Relic physics density

WIMP direct detection: WIMPatomic nucleus in the detector, and detect its recoil (Goodman & Witten, 1985) • Nuclear recoil (NR): recoiling energy ~10 keV • Electron recoil (ER): background (WIMP ER signals’ energy hugely suppressed) 4 Elastic recoil spectrum

. Energy threshold   mass DM  . SI: coherent scattering on all nucleons (A2 Ge Xe enhancement) . Note, spin-dependent Si effect can be viewed as scattering with outer unpaired nucleon. No luxury of A2 enhancement Gaitskell, Annu. Rev. Nucl. Part. Sci. 2004

5 Neutrino “floor” Goodman & Witten

Ideas do exist Phys. Rev. D 90, 083510 (2014) how to go beyond this “floor” (directional, annual modulation, etc), but the pragmatic issue is still how to get there 6 Available hiding space for DM

Elastic spin-independent cross section

a few events/100kg/year Generic WIMP Nature Physics 13, 212– 216 (2017)

7 A “dark matter rush”

8 Background: external

. Cosmogenic background hugely suppressed in underground labs . Remaining external background (gamma, neutrons, and cosmics) can be shielded or vetoed

DarkSide active veto in LNGS

PandaX passive shield in CJPL-I 9 Background: internal

. Detector components (gammas/neutrons)  Cluster @ boundary  Multi-site  Low energy scatter deep in target without high E scattering in outskirt further suppressed! “self-shielding” if reconstruct vertex power of monolithic large detector . (Uniform) background in target, e.g. Rn, Kr . Crucial: further ways to suppress ER background (light/charge ratio, pulse shape, etc …) 10 Detection technologies* CDMSlite Phonons: ~10 meV/ph Electron recoil: background Nuclear recoil: signal

Dark matter Dark matter

DAMA/LIBRA, XMASS Detector CoGENT, CDEX

DEAP, mini-CLEAN DAMIC

electrons:

~10 eV/e~10 ph

PandaX, XENON, LUX/LZ

~10 ~10 eV/ photons: Scintillation Scintillation DarkSide, ArDM

* with representative experiments, not meant to be complete 11 NaI (Tl) experiments

DAMA/LIBRA

• Incompatible with many other experiments (minor model dependence) • Very challenging to make pure NaI crystals • Ongoing NaI projects: SABRE, DM-Ice, COSINE, ANAIS, Cosinus

See Schieck’s talk 12 Cryogenic low threshold detector

Cost per kg Very high*

Difficulty in target scaling Moderate: build arrays

Radioactive isotope Ge/Si can be very pure

Position reconstruction ability iZIP: yes via interdigitated electrodes Surface/volume available via PSD Self shielding Moderate: not monolithic, surface background important ER background suppression Excellent if phonon and ionization detection 10-6 RoI Low mass WIMPs

* difficult to give $/kg due to significant cost on processing/fabrication. 13 D. Bauer SuperCDMS@ Soudan

. Solid-state Ge and Si detectors at < 50 mK. detect ionization and phonon signals from dark matter nuclear recoil scattering . CDMSlite: larger bias c boosts phonon signals e- c Luke Phonons from drifting charges  ΔV low energy thresholds, Recoil Phonons h+ excellent resolution, but

no discrimination 14 D. Bauer SuperCDMS@ Soudan

. Solid-state Ge and Si detectors at < 50 mK. detect ionization and phonon signals from dark matter nuclear recoil scattering . CDMSlite: larger bias c boosts phonon signals e- c Luke Phonons from drifting charges => ΔV Recoil Phonons low energy thresholds, + PRL116,h excellent resolution, but 071301 (2016)

no discrimination 15 D. Bauer SuperCDMS: Soudan to SNOLAB

Designing new SuperCDMS (G2, ～100 kg) experiment for the deeper and cleaner SNOLAB underground laboratory in Canada (operation @ 2020)

16 Point-contact Ge

. LN2 temperature, pure ionization channel . Point-contact detector (small cap ~pF: low electric noise) . CoGENT (Soudan, positive, with annual modulation) and CDEX (CJPL, negative). CDEX long exposure measurement of annual modulation ongoing.

PRL106 (2011) 131301 arXiv:1401.3295 PRD93, 092003

17 Q. Yue CDEX-10 to CDEX-1T

10-kg CDEX ongoing longer term plan of a ton-scale Ge experiment CJPL-II

18 CRESST @ LNGS: low mass record See Turkoglu’s talk . CaWO4 crystals (10 mK) phonon & photons

. 300 eVnr achieved in CRESST-II . CRESST-III with lower mass （24 g) started commissioning 2016,

threshold ~50 eVnr achieved

19 Xe detector

Cost per kg High: ~$1500/kg (material only)

Difficulty in scaling Easy: monolithic

Radioactive isotope Very pure except 136Xe, other than short lived cosmogenic isotopes Position reconstruction ability TPC: excellent (few mm) Single phase: ~cm Self shielding Excellent

ER background suppression TPC: good with charge/light ratio 0.5% Single phase: moderate with PSD RoI Medium to high mass WIMPs

20 XMASS @Kamioka A. Takeda, XeSAT 2017

21 XMASS @Kamioka

A. Takeda, XeSAT 2017

22 Dual phase experiments

23 PandaX-II Dark Matter Run

 First low background run concluded June 2016 with Particle and Astrophysical Xenon 33,000 kg-day exposure. @ CJPL Minimum elastic SI exclusion: 2.5x10-46 cm2 @ 40 GeV/c2

 After the first low background run, experienced some difficulties in background control, which cost an extended down time PRL 117, 121303 (2016)  Now taking dark matter data under an excellent running

condition. 24 PandaX-xT Experiment

. Preparing new experiments in CJPL-II, hall #B2 . Intermediate stage:  PandaX-4T (4-ton target) with SI sensitivity ~10-47 cm2  On-site assembly and commissioning: 2019-2020 . Eventual goal: G3 xenon dark matter detector (~30T) in CJPL to “neutrino floor” sensitivity

25 LUX @Sanford See Lindote’s talk

250-kg LXe . Combination of both science runs (95+332 live-days) . SI cross section limit, 1.1x10-46 cm2 @ 50 GeV/c2, PRL 118, 021303 . Excludes significant portions of the 1-sigma regions for WIMPs favored by certain SUSY models. 26 SeeLZ Lorenzon’s talk

27 See Galloway’s talk XENON1T First Results arXiv:1705.06655

World leading bkg level: 0.210-3 evt/day/kg/keV First SR: 1024 kg x 34.2 day, no candidate found Minimum limit: 7.7 x 10-47 cm2 @ 35 GeV 28 XENONnT

29 See Arneodo’s talk

30 Liquid as detector

Cost per kg cheap

Difficulty in scaling Easy (monolithic detector)

Radioactive isotope 39Ar (1Bq/kg) except using underground Ar (UAr) Position reconstruction ability TPC: excellent (few mm) Single-phase: yes (cm) Self shielding Good

ER background suppression Excellent via PSD (10-8), additional in TPC Energy threshold High (needed for PSD)

31 Argon world running program

DEAP-3600 Mini-CLEAN Single phase Single phase

DarkSide-50 Dual-phase

ArDM Dual-phase 32 DarkSide-50 See Martoff’s talk Phys.Rev. D93 (2016) no.8, 081101

. Pioneered the use of underground Ar . Demonstrated UAr can reduce 39Ar by 1400 times . S2/S1 cuts further suppresses background 33 DEAP-3600@ SNOLAB: 3.6-ton Ar

. Commissioning completed . Collecting data since late 2016. Sensitivity will reach LUX limit by 2017 34 Next stage world Ar program

Mark Boulay, Cosmic Visions 2017

. 20-ton UAr two-phase TPC at DS-20K LNGS . TPC scaled from DS-50 . Crucial technologies: . Low rad. Ar: underground and isotopic depletion . SiPMs for light readout 35 After DS-20K

. Argo/DEAP-nT targeting 1kton-year total exposure . Single/dual-phase considered . Can reach neutrino floor . Site TBD

36 After DS-20K

. Argo/DEAP-nT targeting 1kton-year total exposure . Single/dual-phase considered . Can reach neutrino floor . Site TBD

37 Spin-dependent interaction

. Natural to expect if WIMP has spin

38 Dan Baxter PICO-60: SD c-p coupling Phys. Rev. Lett. 118, 251301 (2017)

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3 8 W -41 discriminate D 10 against alpha S 101 102 103 WIMP mass [GeV/c2] . Blind analysis, 0 events observed, x17 improvement to set world best limit on spin dependent proton coupling 39 131Xe and 129Xe: SD c-n coupling See Lindote’s talk Phys. Rev. Lett. 118, 251302 (2017)

. LUX full exposure limit: 1.6x10-41 cm2 @ 35 GeV/c2 . Collider search complementary for lower mass

40 Recoil directionality: galactic WIMP

D'Ambrosio and Pinci’s talks

See recent updates from www.tir.tw/conf/cygnus2017 Apologies for not going into details! 41 Discovery may be just around the corner

. In next 5 years, number of G2 experiments will turn on and have new results

. Stronger interplay between collider/indirect/direct experiments and the theory community

42 . Many materials borrowed from public talks presented by individual collaborations . Many thanks to Dan Bauer, Qian Yue, Rick Gaitskell, Elena Aprile, Shigetaka Moriyama, Cristiano Galbiati, Juan Collar and Dan Baxter in helping me with the materials

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