PANDA-X
A New Detector for Dark Matter Search
Karl Giboni
Shanghai Jiao Tong University

Seminar at KEK, Tsukuba Japan
3 February, 2011

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Jin Ping Laboratory
Newly constructed deep
underground lab In the south ofChina, Sichuan Province

Now available for installation ofdetectors

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Dark Matter Search2500 m of rockoverburden
About 7500 m.w.e.
25 – 50 Muons per year

A muon veto is
unnecessary

7.5

10-10
JinPing
25 – 50 Muons per year

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The lab was designed and built by Tsinghua University, Beijing and ERTAN
power company
The lab is 40 m x 7 mand 6.5 m high.

PANDA – X will occupy
the last 10 m, but wemust leave half thewidth for trucks to pass.

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PANDA will have a passive shield in
the classical form of
5 cm OFHC copper
20 cm polyethylene
20 cm lead
40 cm polyethylene
In an octogonal shape.
No active shield!
No water shield!
No muon veto shield!
The innermost 5 cm of copper form ahermetic cylinder of 1.35 m diameterand 1.85 m height.
This is also the outer vessel of thevacuum cryostat

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Originally PANDA was intended to be a complement of the XENON100 detector.
However, before the design started the liaison was cut, and the design in nearly
all details is entirely different and fully developed at Jiao Tong.

The Panda team:

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Direct detection of Dark Matter (WIMPs)PANDA-X

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Originally

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Overview of present results

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Charge and light yield dependon Ionisation density

NeArXeWavelengthnm

85128175

Fast Lightnsec

few

103Slow Lightμsec

15.4

1.527

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Advantages of Liquid Xenon

Problems of Xenon

High Density ( 3 g/cm3 )Large Atomic Number ( σsiprop. A2 )Spin Independent + Dependent (131Xe)
Easy Scale up to Large Detector Mass
No Long-Lived Radioactive Isotopes
Efficient Scintillator ( 80 % of NaI(Tl) )No Wavelength Shifter (178 nm)
Transparent to Scintillation Light
Dielectric Strength >few 105 V/cm
Charge depends on Ionization Density

Cryogenic (-100°C )85Kr contaminationVUV lightExpensive

PANDA-X

Dark Matter SearchTechnologies which make large detectors posssible
PTR – Cooling

low maintenance, reliable, stability

VUV - PMTs

optimized for Xe, high Qe, low T, high P, low RI, fast

Recirculation– Purificationelectron drift times > msec

Dual Phase

Charge measurement with proportional scintillation

Liquid Distillation

Kr removal

Combined Charge- Light Signal

very good energy resolution

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WIMP Detection Challenge:

Background Discrimination

Signal: < 0.1 /kg/day (background 106 /kg/day< 100 keVpoint like, no other feature

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Self – shielding effect can be easily seen in data fromXENON100(arXiv1005.0380)

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Additional Background discrimination by light and charge collection

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Overview of present results
Amplification of s2 ≈ 100

Enhanced discrimination due to Gamma – Neutron Band separation
Better position resolution (double hit resolution)Less fiducial volume cut required
But:
Large area grids
HV feedthroughs
High electric fieldin gas space

Precise level contol
Grids must be leveled (parallel to liquid surface)
Large dead time
Large amount of digitizer data

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Higher drift field enhances the Gamma – Neutron band separation

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Example from XENON100: All 22 events in fiducial volume
failed S2/S1 and single hit cut

XENON100
arXiv1005.0380

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Excellent position resolution: 2 mm perp. to el. Field
1 mm along el. field

Mean free paths:

XENON100

MeV Gamma 3 cm
MeV Neutron 30 cm

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Improvements over XENON100:
Less background due to deeper site
Multiple Gamma and Neutron events in larger detector
Better Gamma – Neutron band separation (higher E – Field)
Enhanced light collection
Reduced amount of Teflon
Larger distance of Bottom PMT to Active Volume

But,
No active Veto

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Improvements over XENON100:

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Schematic Lay out of the inner structure of Panda
Anode + Grid
Assembly

Top Array
143 R8520

Liquid Level
Active Volume
Fiducial Volume 25 kg

Cathode Mesh
Cone shapedLight Guides

Bottom Array
37 R11410
3” round

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Panda in it’s Shield
Removable Top Cover

5 cm OFHC copper (outer vessel)
20 cm polyethylene
2 cm OFHC copper
20 cm lead
40 cm polyethylene

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Panda will have a high and uniform light collection efficiency

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The high light collection efficiency at high fields assists inrejecting backgroundPANDA-X

Dark Matter SearchComparison of Xenon based Experiments
Zeplin III

XENON100

XMASS

Fiducial Mass
Total (kg)
Fiducial (kg)1227060

Electron Recoil
Rejection ( % )99.9Energy Threshold(keVr)
Sensitivity at
100 GeV (cm2)
10 GeV (cm2)
StatusLUXPANDA-X

800
100300120259909999.9

1092010510-44>10-422x10-453x10-43

10-45>10-42

3x10-46
4x10-44

4 x10-45
10-44

ScienceRun

Science
Run

Operation

Surface Construction
TestingPANDA-X

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Schedule:

Civil engineering of underground lab completed
Major items ordered, incl. the vessels, cryogenic system, readout electronics, PMTs
Most of the equipment is expected before end of March
Above ground lab at SJTU preparation nearly completed
Above ground tests of complete set up to start in June
Installation of shield underground to start end of MarchCounting facility to be assembled before end of March
Underground installation of detector: September

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SJTU only recently started with xenon technology. A year
ago rather few of infrastructure existed. In the mean time:
Equipped a lab for the development of Panda.
Set up a machine shop to support our activities
Built small test system
Set up gas supply system and recirculation
for high flow rates
Set up PMT test facilityStarted development of Kr removal column
Started development of Read Out system
Started develpment of counting facility in Jin Ping lab

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Dark Matter SearchSome of the recent activities:
Remvable Top Cover