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 10  s 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  t  position 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=1.5  1.0 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/NM (In) [tons] M (InLS) tons PMTs (3”) (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 Events All PMTs PMTs with > 2pe Must reject dark current Simple threshold? More elaborate solution?

Blacksburg - October 14, 2006 Effect of threshold on cascade thresholdpe/MeVrms/mean all pe >1pe/PMT >2pe/PMT >3pe/PMT Air gap Total light output > 2x that w/ air gaps Only 1 pe detected by ~276 PMT’s Introduce threshold at varying levels 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 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% diffuse5% diffuse10% 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 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/m 3  (100 keV)  (200 keV)  (300 keV) % % %  (400 keV) 0.71 %  (450 keV) 0.88 %  (500 keV) 1.03 % P(E  >40keV) =   51 Hz/m 3 (BS) Fold with Pfeiffer E  spectrum