Dark Matter Search with

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Jianglai LiuShanghai Jiao Tong University

On behalf of PandaX Collaboration

Universe today

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Dark matter 26.8%Dark energy 68.3%

4.9%

Ordinary

matter

WIMP Miracle and Detectability

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Indirect detection

Collider search

Direct detection

BSM new physics

Relic density

WIMP

Qiang Yuan and Yufeng ZhouQian Yue and this talk

Galactic halo

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The solar system is cycling the center of galaxy with on average 220 km/s speed (annual modulation in earth movement)

DM local density around us: 0.3(0.1) GeV/cm3 Astrophys. J. 756:89 Inclusion of new LAMOST survey data: 0.32(0.02),

arXiv:1604.01216

Direct detection

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DM: velocity ~1/1500 c, mass ~100 GeV, KE ~ 20 keV

Nuclear recoil (NR): recoiling energy ~10 keV

Electron recoil (ER): due to gamma/beta background

A = m2/m1

WIMP: hide & seek

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Generic WIMP

Elastic spin-independent cross section

a few events/100kg/year

Nature Physics 13, 212–216 (2017)

Bagnaschi,E.A. et al.

Background: external

Cosmogenic background hugely suppressed in underground labs

External background (gamma ray and neutrons) can be shielded or vetoed

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PandaX passive shield in CJPL-I

DarkSide active veto in LNGS

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 …)

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Dual phase xenon TPC

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Detector capability: • Large monolithic target• 3D reconstruction and

fiducialization• Good ER/NR rejection • Calorimeter capable of seeing a

couple of photons/electrons

Dual phase xenon experiments

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LUX, 250 kg, concluded 2016,

Sanford Lab

LZ(7-ton) in preparation

XENON1T

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China Jin-Ping Underground Lab (CJPL-I)

PandaX Experiments

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＝Particle and Astrophysical Xenon Experiments

PandaX-I: 120 kg

DM experiment

2009-2014

PandaX-II: 580 kg

DM experiment

2014-2018

PandaX-III: 200 kg to

1 ton HP gas 136Xe

0vDBD experiment

Future

PandaX-xT:

multi-ton DM

experiment

Future

PandaX collaboration

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Shanghai Jiao Tong University

Peking University

Shandong University

Shanghai Institute of Applied Physics

Yalong Hydropower Company

University of Maryland

University of Science & Technology of China

China Institute of Atomic Energy

Sun Yat-Sen University

Lawrence Berkeley National Lab

Alternative Energies & Atomic Energy Commission

University of Zaragoza

Suranaree University of Technology

Started in 2009, ~50 people

PandaX apparatus in CJPL-I

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PandaX-II Detector

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60 cm x 60 cm cylindrical TPC

580-kg of LXe in sensitive region, 1.2-ton LXe in total

55 top + 55 bottom R11410 3” target PMTs

24 top + 24 bottom R8520 1” VETO PMTs

PandaX-II data taking history

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Run9 =79.6 days, exposure: 26.2 ton-day Run10 =77.1 days, exposure: 27.9 ton-day Largest reported DM exposure to date

2015 2016

Nov. 22 – Dec. 14, Physics commission (Run8, 19.1 days, stopped due to high Krypton background)

Mar. 9 – June 30, low background with 10-fold reduction of Kr (Run9, 79.6 days)

Nov. 2016 – Mar.2017, 2nd distillation campaign and recommissioning

Jul – Oct, ER calibration & tritium removal

2017

Apr.22 – July15, dark matter data taking (Run10, 77.1 days)

July 2017-Now, few months 220Rn/AmBe runs, followed by blinded DM search, 3 x stat of Run 10

2018

Calibration

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Neutron calibration: AmBe source deployed (Energy spectrum measured in Daya Bay detector)

ER calibration using tritiated methane (pioneered by LUX)

Selected data with electron lifetime ~700 s, ~8000 low energy ER events

Jianglai Liu Topical Workshop on DM, IAS, NTU

NR & ER data

Events leaked below the NR median: 0.53(8)%18

99.9% NR acceptance from MC

AmBe band median

Open Red circles: AmBe data Solid Black dots: Tritium dataSolid Blue line: Run9+Run10 median

Jianglai Liu Topical Workshop on DM, IAS, NTU

Run8+9 SI and SD results

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PRL 118, 071301 (2017)PRL 117, 121303 (2016)

Minimum elastic SI exclusion:

2.5x10-46 cm2 @ 40 GeV/c2

33,000 kg-day exposure

Minimum -n SD cross section limit:

4.1x10-41 cm2 at 40 GeV/c2

Run 9 search for axion-electron coupling

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coupling:5x10-12 5x10-13

A + Xe Xe+ + e-

Run9 axion limits

Among the leading axion search on axion-electron coupling using DD experiments

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Solar axions Galactic ALPs

PRL 119, 181806 (2017)

2nd distillation campaign

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After ER calibration, realized that the getter could not remove tritium background effectively

Suspected tritium attached to wall, emanation rate balance with removal rate

2nd distillation campaign (for Kr and tritium)

Nov. – Mar 2017: recuperate distillation refill, flush (closed) detector with warm xenon

First beneficial occupancy of CJPL-II!

ER background budget table

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Run9 Run10127Xe 0.42 0.021

Tritium 0 0.2785Kr 1.19 0.20222Rn 0.13 0.12220Rn 0.01 0.02

Detector ER 0.20 0.20

Solarneutrino

0.01 0.01

136Xe 0.0022 0.0022

Total 1.96 0.79

Original 127Xe gone, additional introduced by a bottle of surface xenon during distillation

Based on best fit to data (later)

Rest are consistent between Run 9 and Run 10

Unit: mDRU = 10-3/keV/day/kg0.8 mDRU ~ 2 events a day!

Energy spectrum in Run 10

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[0,50] keV DM search range

Data and expected background in good agreement

Distribution of events

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Appears to have a downward fluctuation of background (p value 7% for Run 9+10)

Run 9 Run 10

WIMP-nucleon SI results

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Improved from PandaX-II 2016 limit about 2.5 time for >30GeV/c2

Lowest exclusion at 8.6×10-47cm2 at 40GeV/c2

Most stringent published limit for WIMP-nucleon cross section for mass >100GeV/c2 to date

PRL 119, 181302 (2017)

Linear in mass

WIMP-nucleon SD results (54 ton-day)

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Minimum -n SD cross section limit:

1.6x10-41 cm2 at 40 GeV/c2

Minimum -p SD cross section limit:

4.4x10-40 cm2 at 40 GeV/c2

More general EFT analysis completed

Soon to be appeared on arXiv

XENON1T 1ton-year result

XENON1T released their 1ton-year exposure search in May

Background fluctuation p value: 22%, best fit: 1.7 DM particles below the NR median

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XENON1T arXiv:1805.12562

Self-interacting DM search

Astrophysical observations: SIDM could solve long standing “small-scale puzzle” and “diversity problem” for galactic rotation

A. Kamada, M. Kaplinghat, A. Pace, and H. Yu, PRL 119, 111102

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Dark mediator for the SIDM

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Interaction strength of dark mediator with SM: 2/m4

NR spectrum softer than the traditional WIMP

arXiv:1802.06912, PRL accepted

SIDM constraints from PandaX-II

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Put serious constraints on parameter region favored by dwarf galaxies observations

Future: CJPL-II

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PandaXCDEX

B2 experimental hall

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PandaX-xT

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Intermediate stage: PandaX-4T (4-ton target) with SI sensitivity ~10-47 cm2

On-site assembly and commissioning: 2019-2020

Sensitivity of PandaX-4T

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arXiv:1806.02229

B2 experimental hall

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Project progress

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Low background cryostats Cooling bus

TPC

Low temp PMT testing chamber

Ultralow concentration Kr assay

Low threshold trigger system

PandaX-III: High pressure 136Xe TPC

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0DBD signal: two electrons emitting from the same vertex with a summed energy at the Q value (tracking essential)

TPC: 200 kg, 10 atm, symmetric, double-ended charge readout plane with micromegas module with cathode in the middle

Four more upgraded modules for a ton scale experiment

Published CDR recently: arXiv:1610.08883

Jianglai Liu Topical Workshop on DM, IAS, NTU

20-kg scale prototype at work

39Jianglai Liu Topical Workshop on DM, IAS, NTU

Summary and outlook

PandaX-II continues to probe the forefront of the dark matter particle models

2018 expected completion of PandaX-II

Exciting upgrade plans and future opportunities at CJPL-II for PandaX

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