LENS The Lattice Architecture Jeff Blackmon ORNL on behalf of LENS Collaboration

1
LENS - The Lattice ArchitectureJeff Blackmon
(ORNL) on behalf of LENS Collaboration
The Basic LENS Concept
8 Indium-loaded liquid scintillator
(pseudocumene) High light output gt8000
h?/MeV Long attenuation length gt8m
Crucial breakthrough See next talks
1 prompt electron ? ?e energy (?-like)
signal 1
signal 2
Buffer up to 10?s
Shower Time/space correlation
discrimination
(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)
2
Longitudinal Design Classic LENS
Typically 3x3 modules (5m long) with PMTs on
ends
Extensive simulations Russia, VaTech, ORNL
End view
?t?position
?30 cm localization along length
Energy must be deposited in 2 of 8 neighbors for
good discrimination
Efficiency 35
3
LENS The Lattice Architecture
Monolith segmented with double-pane nylon
trapped air
Cartoon representation (2D)
Fresnel reflections n1.5?1.0
air
In-loaded scintillator
Laser demonstration at P2atm
Full 3D segmentation for LENS Nearly perfect
digital event localization Antireflective
coatings can reduce losses
4
A Tale of Two Sims
Two independent modeling efforts with somewhat
different approaches
(1) Track every optical photon
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
5
Cascade vs. 2? background (5x6m)3

• Light output lower than expected
• 708 pe/MeV (VaTech 950 pe/MeV)

??
Cascade
Cascade
??
6
LENS Design Figures of Merit
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

7
The Hard Lattice
No trapped air Easier construction More
robust Most photons channeled ?crit60? Good
event localization Less trapping Greater light
output
Solid Teflon Segmentation
Challenges How to deal with spray? Background
rate Trigger logic
8
Dark current
Each ? decay fires 150 PMTs (5) Total decay
rate 4MHz (6m)3 1 of PMTs fire every 250
ns 20 decays between ? and cascade
Events
All PMTs
Must reject dark current
Simple threshold? More elaborate solution?
PMTs with gt 2pe
Events
Number of PMTs firing
9
Effect of threshold on cascade
All pes

• Total light output gt 2x that w/ air gaps
• Only 1 pe detected by 276 PMTs
• Introduce threshold at varying levels

Cascade
?
gt2 pe/PMT
Cascade
?

• Threshold hurts energy resolution
• Light output still better than air gap

10
Hard lattice results
11
Towards a better analysis

• With the most simple cuts, hard lattice
  performance is worse

but the jury is still out

• Were currently investigating a larger parameter
  space

pe1/pesum
pe1/pesum

• More sophisticated approaches
• Maximum likelihood
• Neural network algorithm

12
Optical imperfections

• Fine segmentation ? treatment of optical
  properties is very important

4 Types of reflection at boundary
GEANT4 Optics

• Specular spike
• About average surface normal
• Specular lobe
• About normal of micofacet
• Diffuse lobe
• Lambertian diffuse scattering
• Backscatter spike
• About average surface normal

• Little data on optical properties for detector
  materials
• Measurements needed
• Parameterized simulations

13
Lambertian scattering in air gap
1 diffuse
5 diffuse
10 diffuse
specular

• Total pes not significantly affected
• Increasing diffuseness rapidly spreads the pes
• Reconstruction difficult
• Dark current problem similar to the hard
  lattice

all pes
?gt2pe/PMT
14
5 Lambertian in air gap
Same analysis assuming ? all pe
15
Summary
Longitudinal Design
The LENS concept is robust
3 viable detector designs
Modular approach
Best potential performance
Most straightforward construction
Benchmarking simulations to lab data Prototyping
Optical properties important
16
Bremsstrahlung
Beta decay rate 19 kHz/m3
P(E?gt40keV) 0.00270
51 Hz/m3 (BS)
??(400 keV)
0.71
??(450 keV)
Fold with Pfeiffer E? spectrum
0.88
???
?
??(500 keV)
1.03