blacksburg - october 14, 2006 lens - the lattice architecture jeff blackmon (ornl) on behalf of lens...
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Blacksburg - October 14, 2006
LENS - The Lattice ArchitectureJeff Blackmon (ORNL) on behalf of LENS Collaboration
8% Indium-loaded liquid scintillator (pseudocumene)
High light output >8000 h/MeV
Long attenuation length >8m
signal #1
signal #2
#1 prompt electron e energy (-like)
discrimination
Buffer up to 10s
ShowerTime/space correlation
(~6 m)3 fiducial volume ~15 tons Indium
~ 500 pp events/yr (50% eff.) 3% measurement in a few years
Critical issues: light collection & resolution (space/time)
The Basic LENS Concept
Crucial breakthroughSee next talks
Blacksburg - October 14, 2006
Longitudinal Design: Classic LENS
Typically 3”x3” modules (~5m long) with PMTs on ends
End view
tposition
Energy must be deposited in 2 of 8 neighbors for good discrimination
30 cm localization along length
Extensive simulations: Russia, VaTech, ORNL
Efficiency ~35%
Blacksburg - October 14, 2006
Monolith segmented with double-pane nylon & trapped air
LENS: The Lattice Architecture
Fresnel reflections n=1.51.0
Laser demonstration at P~2atm
Cartoon representation (2D)
Full 3D segmentation for LENS
Nearly perfect “digital” event localization
Antireflective coatings can reduce losses
In-loaded scintillator
air
Blacksburg - October 14, 2006
A Tale of Two SimsTwo independent modeling efforts with somewhat different approaches
Decouple optics from background studies
(1) Study pe/MeV yield for each geometry
(2) Compare pe/PMT distribution
Like “real life”
Study optical imperfections
Reconstruction & trigger development
(2) Background studies: E(x)
Fast
(1) Track every optical photon
Blacksburg - October 14, 2006
Cascade vs. 2 background (5”x6m)3
• Light output lower than expected» 708 pe/MeV (VaTech = 950 pe/MeV)
Cascade
Cascade
Radius
40.4%
0.24%
Impose 2 very simple cutsImpose 2 very simple cuts
7.8/ton/yr7.8/ton/yr
Blacksburg - October 14, 2006
LENS Design Figures of Merit
Cell Size [mm]
Cube size [M]
pe/MeV
Det. Eff [%]
Nu/t In/y
Bgd/t In/y
S/N M (In)[tons]
M (InLS) tons
PMTs
75 5 1000 64 40 13 3 10 125 13300(3”)
125 6 950 40 26 9 2.9 15.3 190 6250(5”)
Signal and Background in LENS Christian Grieb, Virginia Tech, October 2006
• Excellent agreement with efficiency & background rate (geometric)
• Still looking at difference in light: 708 pe/MeV vs. 950 pe/MeV
Blacksburg - October 14, 2006
The “Hard Lattice”No trapped air
Easier construction
More robust
Most photons “channeled” crit~60
Good event localization
Less trapping
Greater light output
Solid Teflon Segmentation
Challenges:
How to deal with “spray”?
Background rate
Trigger logic
Blacksburg - October 14, 2006
Dark currentEach decay fires ~150 PMT’s (5”)
Total decay rate ~4MHz (6m)3
1% of PMTs fire every ~250 ns
~20 decays between and cascade
Number of PMTs firing
Eve
nts
Eve
nts
All PMTs
PMTs with > 2pe
Must reject dark currentMust reject dark current
Simple threshold?
More elaborate solution?
Blacksburg - October 14, 2006
Effect of threshold on cascade
threshold pe/MeV rms/mean
all pe 1584 0.041
>1pe/PMT 1132 0.066
>2pe/PMT 948 0.060
>3pe/PMT 890 0.054
Air gap 708 0.056
• Total light output > 2x that w/ air gaps
• Only 1 pe detected by ~276 PMT’s
• Introduce threshold at varying levels
Cascade
Cascade
All pe’s
>2 pe/PMT
• Threshold hurts energy resolution
• Light output still better than air gap
Blacksburg - October 14, 2006
Hard lattice results
Impose the same 2 cutsImpose the same 2 cuts
52%
0.48%
40% & 0.24%Double-foil
Blacksburg - October 14, 2006
Towards a better analysis• With the most simple cuts, hard lattice performance is worse …
… but the jury is still out
• More sophisticated approaches:
» Maximum likelihood
» Neural network algorithm
39%
0.35%pe1/pesum pe1/pesum
• We’re currently investigating a larger parameter space
Blacksburg - October 14, 2006
Optical imperfections
• Specular spike» About average surface normal
• Specular lobe» About normal of micofacet
• Diffuse lobe» Lambertian “diffuse” scattering
• Backscatter spike» About average surface normal
• Fine segmentation treatment of optical properties is very important
4 Types of reflection at boundary
• Little data on optical properties for detector materials
» Measurements needed
» Parameterized simulations
GEANT4 Optics
Blacksburg - October 14, 2006
Lambertian scattering in “air gap”1% diffuse 5% diffuse 10% diffusespecular
• Total pe’s not significantly affected
• Increasing diffuseness rapidly spreads the pe’s
• Reconstruction difficult
• “Dark current” problem similar to the “hard lattice”
all pe’s
>2pe/PMT
Blacksburg - October 14, 2006
Cascade
5% Lambertian in “air gap”
Same results
~40%
~0.3%
Same analysis assuming all pe
Cascade
What if we impose >2pe/PMT threshold?
Similar results are possible
Low light yield is more problematic for single
Blacksburg - October 14, 2006
SummaryThe LENS concept is robust
Hard Lattice
Solid teflon segmentation
Scintillation Lattice
Double-layer nylon lattice
Longitudinal Design
3 viable detector designsModular approach
Best potential performance Most straightforward construction
Optical properties important Benchmarking simulations to lab dataPrototyping