Search for Dark Matter at CJPL with PANDAX

Kirill Pushkin for the PANDAX Collaboration,

10th Rencontres du Vietnam, Very High Energy Phenomena in the Universe,

August 3-9, 2014

Contents

• Introduction• Experiment • Commissioning. Data taking.• Prospects and summary

PANDAX: Particle and Astrophysical Xenon

The PANDAX Collaboration

• Collaboration started in 2009 (includes ~40 people)

• 7 institutions

Shanghai Jiao Tong University,

Shandong University,

Shanghai Institute of Applied Physics, CAS,

Beijing University,

Yalong Hydropower Co., Ltd.

http://pandax.org

University of Michigan (USA)University of Maryland (USA)

China JinPing Underground Laboratory (CJPL)

• ~2400 m overburden of rock• Deepest underground lab in operation

6720 m.w.e. ~57 muons/(year x m2)• Low radioactivity marble rock • Easy access – located in the middle of the 18 km tunnel

• μ – veto system unnecessary• compact shielding structure possible• easy access by road• future plans for CJPL II

CJPL

SURFSURF

Current layout of CJPL

The PANDAX laboratoryXe detector

Ge counting station Storage bottles with Gas Xenon

The PANDAX Detector

• Dual phase Xe detector• Probing WIMP-nucleon cross section• Designed for 1 T fiducial mass

Stage I: 125 kg xenon target, 400 kg total massStage II: 500 kg xenon target, 1.3T total massStage III: 1.5 ton target, 3T total mass

III stages for PANDAX

Stage I

Stage II

Stage III

External shielding

Passive shield Rn purge with N2 gas

• Reduces background from surrounding rocks and concrete• Passive shield allows accommodating a large, 1T, scale detector

• Continuous flush with boiled-off LN2

• Levels of Rn achieved < 1 Bq/m3 (limited by thesensitivity of the used Rn detector

CryogenicsCooling power ~180 W (-96 degrees of Celsius)

LN cooling Heat exchangerPulse Tube Refrigerator

Stage I TPC

Detector characteristics:

• TPC radius: 30 cm• Drift length: 15.4 cm

• Total Xenon mass: 400 kg• Sensitive target: Xe mass: 125 kg• Fiducial volume: Xe mass 37 kg

• Top PMTs array (1”, R8520): 143• Bottom PMTs array (3”, R11410): 37

PANDAX- Stage I

Background control: Detector materials counting

Use materials with low radioactivity: 238U, 232Th, 40K, 60Co

PANDAX Stage I Progress

PMT calibration with LEDs

LED calibrations:• 2 Teflon ball diffusers on top PMT array• LED and diffusers are coupled to optical fibers and feedthroughs• Gains balanced at ~2x106

Calibration data systemWe can insert a gamma or neutron source into the tubing to calibrate the detector

3D position reconstruction important for further background reduction

Xenon purity

• Electron lifetime ~262 us (drift time 20-80 us)

S2 vs S1 light anticorrelation

40 keV (Xe-129)

80 keV (Xe-131)

Gamma background rejection

Radioactive background: Kr in Xe

• We employ a home made distillation column to remove Kr from gaseous Xe.

• We use an ultrasensitive Purity Analysis System based on RGA (MKS E-Vision 2).

• The amount of Kr-84 in our Xe after the distillation is of the order of ppt which can be subsequently recalculated in to the amount of Kr-85 in Xe.

Radioisotope Kr-85, T1/2=10.756 years. Beta maximum energy decay 687 keV

Kr-Xe distillation system

Calibration measurements of Kr-84 in Xe gas

Measured by K. Pushkin and He Min Purity Analysis System

Sensitivity projection (Stage I after 100 days of taking data)

Stay tuned for the Physics Results (17 days Dark Matter data paper will be released VERY SOON)

Leff cutoffbelow 3 keVLeff no cut offbelow 3 keV

Upgrade: Stage II

Goals:• Upgrade in preparations. Stay tuned for more exciting news• Sensitivity reach 2x10-46 cm2 at 100 GeVwith 54000 kg-day.

Future plans: CJPL-II

Summary

• PANDAX has made a good progress in the past year. Currently, the experiment is taking data.

• Stay tuned for the coming 17 days Dark Matter data paper (expected to appear VERY SOON on arXiv).

• Currently, we are upgrading the detector, Stage I, to Stage II.

Thank you for your attention!