Blacksburg - October 14, 2006

LENS - The Lattice Architecture Jeff 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

Shower Time/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 breakthrough

See 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 Sims Two 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 cuts

7.8/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 current

Each 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

E

ve

nts

All PMTs

PMTs with > 2pe

Must 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 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% diffuse specular

• 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

Summary

The LENS concept is robust

Hard Lattice

Solid teflon segmentation

Scintillation Lattice

Double-layer nylon lattice

Longitudinal Design

3 viable detector designs Modular approach

Best potential performance Most straightforward construction

Optical properties important Benchmarking simulations to lab data

Prototyping

Blacksburg - October 14, 2006

Bremsstrahlung

Beta decay rate = 19 kHz/m3

(100 keV)

(200 keV)

(300 keV)

0.036 %

0.190 %

0.423 %

(400 keV) 0.71 %

(450 keV) 0.88 %

(500 keV) 1.03 %

P(E>40keV) = 0.00270

51 Hz/m3 (BS)

Fold with Pfeiffer E spectrum