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
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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
• μ – veto system unnecessary
• Deepest underground lab in operation
• compact shielding structure possible
2
6720 m.w.e. ~57 muons/(year x m )
• easy access by road
• future plans for CJPL II
• Low radioactivity marble rock
• Easy access – located in the middle of the 18 km tunnel
CJPL
SURF
SURF
Current layout of CJPL
Ge counting
station
The PANDAX laboratory
Storage bottles with Gas Xenon
Xe detector
The PANDAX Detector
• Dual phase Xe detector
• Probing WIMP-nucleon cross section
• Designed for 1 T fiducial mass
III stages for PANDAX
Stage I
Stage III
Stage I: 125 kg xenon target, 400 kg total mass
Stage II: 500 kg xenon target, 1.3T total mass
Stage III: 1.5 ton target, 3T total mass
Stage II
External shielding
Passive shield
• Reduces background from surrounding
rocks and concrete
• Passive shield allows accommodating
a large, 1T, scale detector
Rn purge with N2 gas
• Continuous flush with boiled-off LN2
• Levels of Rn achieved < 1 Bq/m3 (limited by the
sensitivity of the used Rn detector
Cryogenics
Cooling power ~180 W (-96 degrees of Celsius)
LN cooling
Pulse Tube Refrigerator
Heat exchanger
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 system
We 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
80 keV (Xe-131)
40 keV (Xe-129)
Gamma background rejection
Radioactive background: Kr in Xe
Radioisotope Kr-85, T1/2=10.756 years. Beta maximum energy decay 687 keV
• 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.
Kr-Xe distillation system
Calibration measurements of Kr-84 in Xe gas
Integrated partial pressure over 10min (AU)
c2 / ndf
18.41 / 12
p0
2.792e-10 ± 6.895e-11
p1
38.52 ± 2.145
10-8
10-9
10-11
10-10
10-9
Concentration of Kr in Xe (mol/mol)
Measured by K. Pushkin and He Min
Purity Analysis System
Sensitivity projection (Stage I after 100 days of
taking data)
Leff cutoff
no cut off
below 3 keV
Stay tuned for the Physics Results
(17 days Dark Matter data paper will be released VERY SOON)
Upgrade: Stage II
Goals:
• Upgrade in preparations. Stay tuned for more exciting news
• Sensitivity reach 2x10-46 cm2 at 100 GeV
with 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!