PANDA-??
A New Detector for Dark Matter Search
Karl Giboni, Xiangdong Ji, Andy Tan, Li Zhao
Shanghai Jiao Tong UniversitySeminar at KEK, Tsukuba Japan
24 November, 2011

PANDA-X

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

Depth: 7500 m.w.e.
Low radioactivity rock

PANDA-X

Dark Matter Search

Double Phase approach, i.e. discrimination by light and charge collection

PANDA-X

Dark Matter Search

Schematic Lay out of the inner structure of Panda (25 kg)
Anode + GridAssemblyTop Array
143 R8520

Liquid Level
Active Volume
Fiducial Volume 25 kg

Cathode Mesh
Cone shapedLight Guides

Bottom Array
37 R11410
3” round

PANDA-X

Dark Matter Search

Inner structure of Panda ready to be installed.

PANDA-X

Dark Matter Search

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

Shield construction will
start in December(about 60 days)

PANDA-X

Dark Matter Search

Test Set Up for Panda in aboveground lab (Shanghai).
LN2HeatCoolingPTRExchanger

Outer Vessel(about 1.2 m into ground)

PANDA-X

Dark Matter Search

Gas Storage system. Only
One 300 kg (80 bar) gas
cylinder and dewar is nowinstalled.
SAES Getter in background.
All behind cryogenic system

PANDA-X

Dark Matter Search

Inner vessel currently baking
under vacuum.

This SS vessel is only fortests. The final vessel willbe Ti

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Development Plan

The shield and the outer vessel are sufficiently large
500 kg: PTFE panels, Shaping Rings to be replaced
1000 kg: New detector structure in larger inner vessel

25 kg

500 kg1000 kg

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Summary

Panda-X is being assembled in lab aboveground
Installation underground in early spring 2012
Detector can be easily expanded from 25 kg up to 500 kg
1000 kg detector is planned. This detector requires new
inner structure, new inner vessel and many more PMTs.
Space in JinPing lab, passive shield, and cryogenic system
are already foreseen for 1 ton detector

However, scale up of LXe detectors is becoming increasinglydifficult. Some details of the design have to be changed forthe 1 ton ( or larger) detector.

PANDA-X

Problems with DesignLeveling and Level Control
Make design much more
complicated.
Leveling and Level Control
are not desirable
Remove Overflow ChamberandLevel Glides

Overflow chamber adds alot of material, i.e.
backgroundPANDA-X Problems with Design
Anode-Cathode distance:
84 cm
At 1 kV/cm: 84 kV
Max drift time: 415 µsec
Anode with typically 5 kV
in gaseous xenon
Cathode HV too close toBottom PMTs
HV feedthrough is not soeasy to realize above 50 kV

PANDA-X Problems with DesignTop PMT make too muchbackground

Light guide cones lessefficient than expected
Too many PMTs on Topand Bottom.
Too many electronic channels
Background dominatedby PMTs and bases
Too many cables

PANDA-X Problems with Design

Light efficiency reduced byPTFE reflector panels.

PTFE makes problems withbackground1 ton PANDA-X

Everything else is okay
and does not have to bechanged!

We need a new, different
concept for Panda ??

1 ton PANDA-X
Proportional Scintillation in liquid
xenon with small test chamber
Very thin wire 4 µm
Proportional counter 6 mmdiameter
HV up to 3 kV
Homogeneous field in drift
space, radial field aroundanode wire.
Miyajima et al., NIM160(1979)239

1 ton PANDA-X
Results with α - source
Charge gain observed atlarge fields
Charges nearly saturate at
1 kV, but increase again
above 1.5 kV, when charge
multiplication starts
However, charge multiplication adds more
fluctuations, i.e. loss in energy resolution.
Limitation to Proportional Scintillation night bebetter1 ton PANDA-X
Drifting electrons are accelerated in
between collisions by the electricfield. But, below a threshold energy
they can not start an electron
avalanche.

There is a plateau at no gain
between 1 kV and 1.5 kV.
The acceleration is not sufficiently
strong to start an avalanche, but Xe
atoms can be excited and photons
can be created above a much lowerthreshold.

1 ton PANDA-X
The energy resolution canget much worse due tocharge multiplication.

But energy resolution notvery important for WIMP
search. A small charge gain
can be tolerated

1 ton PANDA-X
Direct and secondary
scintillation pulses at 1.6 kVand 3.0 kV.

The time scale is the same,but the amplitude scale isreduced by a factor 2.

1.6 kV

3.0 kV

Secondary scintillation pulses at
2.8 kV.
The time scale is 200 nsec/iv.)

1 ton PANDA-X

Light at different voltages.
At 1.6 kV nearly no charge
gain, but a factor 10 morelight.

We do not need a large light gain.
A very large difference between
primary and secondary light does
require a very large dynamic
range!

1 ton PANDA-X

Typical direct scintillation pulse.
(50 nsec/div)

Different geometry, similar
results, but also thicker wires.

Masuda et al., NIM160(1979)247

Secondary scintillation pulse.
(200 nsec/div)

1 ton PANDA-X
Energy resolution for
Prop. Scintillation and Charge

Energy resolution of
Proportional Scintillationcomparable to charge
measurement with CSA.

However, energy resolution
will be much better withCharge – Light combination

1 ton PANDA-X

20 µm wires
We should operate just at theonset of charge multiplication

1 ton PANDA-X
At SJTU we will study
Proportional
Scintillation in liquid with asmall test chamber.

System is ready to start tests.

1 ton PANDA-X
Pieces for the test detector
are already prepared.

Simple gridded IonizationChamber with Charge andLight Read Out

1 ton PANDA-X
With Proportional Scintillationin liquid xenon, all the structure
can be immersed.
Up and down are equivalent,
and we can make several driftregions.
Example: 4 drift regions, 21 cm
length each.
Two cathodes and 3 anode –grid assemblies.
Liquid level far above top
anode assembly

Liquid Level

ACACA

The New and Improved PANDA-1T
Advantages: 1. Liquid level far above top anode2. No leveling necessary
3. For 1 kV/cm total HV 21 kV instead of 85 kV
4. Cathode (HV) far from Bottom Photo Sensor
a. No problem with high E - fieldb. No γ-rays interacting in front of PMT
5. Max. drift time 105 µsec instead of 420 µsec
a. Less purity requirementb. Less dead timec. Less digitized data
6. No Anode HV in gaseous xenon.

Light Read Out for PANDA-1T
Arrangement of photo sensors in the LXe:
Top and bottom array fully symmetric :Both will be used for S1 and S2 detection
Light cones not very effective (will be removed)
Sides have to be covered by sensors.
Usual requirements still valid:a. Immersed in liquidb. Operating temperature -110 C
c. Pressure > 3 bar
d. High Qe (and also Collection Efficiency)e. Large coverage of areas
f. Low radioactivity

Light Read Out for PANDA-1T
Simulation of Panda 25k shows that lightcollection is not symmetric. And the 25
kg is already the best case!

Light Read Out for Panda 1T
Only choice: Gaseous Photo Multiplier
ThickGEM single stage
Micromegas for additional gain
CsI Photocathode
Transparent PhotocathodeUV-Quartz Envelope
A lot of work development work already done byAmos Breskin (Weizman Institute) and others.
Main job left: Packaging

SJTU wants to join RD51 collaboration in February 2012

Light Read Out for Panda 1T
Size 8” x 8” (or 8” x 4”), Pixel size about 1” x 1”
Sides : 60 pieces (to be optimized)
Top, Bottom 30 + 30 pieces (to be optimized)
Ar- CF4 - 95%-5%Transparent PhotocathodeUV Quartz Window
CsI PhotocathodeThGEM

Micromegas

The New and Improved PANDA-1T
Final size, aspect ratio, andrelative location in thevessel to be optimized.
Field shaping by wire rings
hold in place by supportstructure.
A lot of work ahead, but noproblems in principle.
Final performance to beevaluated with simulations