Measuring the Low Energy Solar Neutrino Spectrum LENS-Sol SNOLAB Workshop, Sudbury, Aug 15, 2005 R. S. Raghavan Virginia Tech

LENS-Sol / LENS-Cal Collaboration (US-Russia) ( ) Russia: Institute of Nuclear Research (INR Mosow) I. Barabanov, L. Bezrukov, V. Gurentsov, V. Kornoukhov, E. Yanovich INR (Troitsk) V. Gavrin et al; A. Kopylov et al U. S. BNL A.Garnov, R. L. Hahn, M. Yeh ORNL J. Blackmon, C. Rascoe, A. Galindo-Urribari Princeton: J. Benziger U. North Carolina A.Champagne V. T. Z. Chang, C. Grieb, M. Pitt, RSR, R.B. Vogelaar R.S.Raghavan/VT/June05

LENS-Sol GOAL: Experimental Measurement of the Neutrino Luminosity of the Sun (3-4%)  Measure the low energy neutrino spectrum (pp, Be, …) in real time & with precision  Exptal Tool: Tagged CC Nu Capture in Indium ν e In  e - + (delay) 2 γ Sn solar signal tag

LENS-Sol-- Low Energy Solar Nu Spectroscopy via Indium --Basics CC Nu Capture in 115 In to excited isomer in 115 Sn Tag: Delayed emission of 2 γ’s Threshold: 114 keV  pp Nu 115 In abundance: ~96% Basic Bgd Challenge: Natural β-radioactivity of In In β-Spectrum overlaps pp signal (Be, CNO not affected β max energy = tag energy R.S.Raghavan/VT/June05

LENS-Sol Signal= [SSM(low CNO)+LMA] x Detection Efficiency: pp ~ 40%; Be 85%; pep 90%  Rate: pp 25 /y /t In For pp ± 3%, need 2000 ev. / 5y Signal Electron Energy (MeV) Expected Result: Nu- capture Signature: Isomeric Coincidence decay with τ =4.76 µs Bgd measured concurrently with signal S/N~1 Adequate For Precision Flux S/N=1 S/N= pp events (0-10 µs) generated: Fit S=2044±62; (3.1%) S/N=1 (in 0-10µs) Fit S=2031±51; ( 2.5%) S/N=3 Random coinc bgd signal pp 7 Be pep CNO Detector Resolution Included (800 pe/MeV) ~10 keV det. threshold

NEW SCIENCE—Discovery Potential of LENS Solar Nu spectrum <5 MeV Yet UNOBSERVED after 40 y of solar nu’s !!! APS Nu Study 2004  Lo Energy Solar Nu Spectrum: one of 3 Priorities R.S.Raghavan/VT/June05 In First two years of Data (No source Calib needed) Proof of MSW LMA Physics from P ee of pp & Be nu --No proof yet! (no d/n effect, spectral shape a problem?) Non-standard Fundamental Interactions? CPT Invariance of nus ? RSFP/ Nu magnetic moments—Time dependence? In Five Years (with source Calib ): pp Be fluxes measured to 3% First Exptal test of Neutrino Luminosity  Photon Luminosity Ultimate test of Neutrino Physics and Solar Astrophysics Neutrino Physics: Precision Measurement of θ 12 θ 13 Sterile Neutrinos? Astrophysics: Is the Sun getting Hotter? Hidden new source of energy of Sun?

LENS: Studied world wide since 1976 ! - Dramatic Progress in  2005 Longitudinal modules + hybrid design In: 30 ton for 1900 pp’s /5y Total mass LS: 6000 ton PMTs: ~200,000 or Cube lattice or non-hybrid longitudinal modular design In: ~14 ton for 1970 pp’s /5y Total mass In LS : ~175 ton PMTs: ~6,500 ( MPIK Talk at DPG 03/2004)

LENS Progress - - How?-- Major Advances in Scintillator Chemistry Absorption length ~ 5% In > 8% In Module size: ~ 1.5m ~ 6m Photoelectron yield:~ 230 pe/MeV ~ 900 pe/MeV + high energy resolution : Structure of internal 115 In Bgd: partial study (1 component) complete study (5-6 comps.) only single-  decay with BS multi-  decays with or w/o BS considered 498keV  from decay to 115 Sn * (single-  decay not dominant!) New Insights in Analysis Strategy Old: pp-efficiency: ~ 20%New: ~ 45% Signal/Noise: ~ 1~ 3 New Detector design: Design:Hybrid Hybrid design obsolete Longitudinal modules - Cube lattice - Event location analog- via PMT timing Event location digital 2004  2005

Components of Indium radioactive bgd In115 Sn115 β0, γ0 (BS) (Emax = 498 keV) β1 (Emax< 2 keV) (1.2x10 -6 )* 498 keV BGD 0-300(e1) 116 (g2) 498(g3) In SIGNAL R.S.Raghavan/VT/June05 * Cattadori et al (2003) Sn In tag search volume around vertex of initial beta, occurrence of a random event with minimum Nhit =3 1 beta decay: A1 = beta + BS gamma (E tot = 498 keV) A2 = 498 gamma 2 beta decays in random coinc: B = beta, BS or 498 in any combination from each beta decay 3 beta decaysin random coinc : C = 3 betas mostly 4 beta decays in random coinc: D Only A1 considered up to 2004 ! * Cattadori et al: 2003

Tag topology x Tag Energy 1.4x x10 5 B 3x x10 3 A2 2.6x x10 4 A1 3x Min 3 Hits 2.8x x10 11 (Singles) In Bgd /ton In/y 62.5Vertex Del.Coinc. (Granularity: 35g/ton) 62.5 (singles) RAW Signal /ton In/y Bgd Suppressed by a factor ~10 11 Signal Loss Factor ~2 Task of Design and Analysis is to suppress bgd by only 3x NOT ~10 11  Generate 4x10 6 events for analysis Role of Experimental Tools in Bgd Suppression in LENS-Sol

Basic Design Vectors Detection Technology: In loaded liq. Scintillator (InLS) (E resln) Advances in Scint. Chemistry DetectorArchitecture: Segmented /Granularity ~1kg/100 ton New Design Bgd Suppression at high Det. Efficiency New Analysis Strategy

InLS (PC:PBD/MSB): hν / MeV BC505 Std hν/MeV In 8%-photo Light Yield from Compton edges of 137 Cs γ-ray Spectra PC NEAT ZVT27; Abs/10cm=0.004; L(1/e)=10.8 m ZVT28,32: Abs/10cm=0.002; L(1/e)~20m In LS Status (July ‘05) – Summary 1 Indium conc. ~8 wt% (higher may be viable) 2.Scintillation signal eff (typical): 9000 hν/MeV 3.Transparency at 430 nm: L(1/e) (typical): 10 m 4.Chemical and Optical Stabililty: ~ 2 years 5. InLS Chemistry Robust (>1000 syntheses ) Milestones unprecedented in metal LS technology LS technique relevant to wide science experiments Basic Bell Labs patent Applied 2001; awarded: 2004 R.S.Raghavan/VT/Aug 05

Detector Design:---Segmented Objective: Moderate Granularity (~1kg/100 T) Two Approaches for close packed architecture: Longitudinal Modules (1-D) (“classical”) Scintillation Lattice “chamber” ( 3-D ) (new) Both Designs under study Scintillation Lattice Design Details in this talk R.S.Raghavan/VT/June05

GEANT NEW DETECTOR CONCEPT— SCINTILLATION LATTICE ( RSR ’93) Concept Simulation: ideal optics Light output 75% (6PMT) vs 50% (2PMT) in long. modules Precise 3D Digital Event Localization ~10cm v. 60 cm (±2 σ) in longitudinal modules Event localization independent of event energy Particle tracks, γ-ray shower structure directly seen reconstructed hit times  reduced randoms

Perfect optical surfaces Ideal optics: 20 pe rough optical surfaces: 20% of light with non-ideal optics: 12 pe in vertex + 4pe in “halo” Vertex definition in non-smooth optical channels 12.5 cm cells in 4x4x4m cube 100 keV event /9000 hν/MeV Total signal 6x16=96 pe

7.5cm cells 700 pe/MeV 12.5cm cells 950 pe/MeV 18cm cells—1100 pe/MeV 5x5x5m Cube

Analysis Basic Constraining Tools: (key for (A1, A2) 1. Total Shower Energy of tag candidate (g2 energy in vertex wide open) 2. No. of hits in tag candidate shower (key for B, C, D…) 3. Shower sphere radius 4. Maximum inter-hit distance 5. e1-g2 coincidence window 10µs R.S.Raghavan/VT/June05

nu events g 2 +g 3 Total Tag Energy BS >450 kev 498 Before Cuts Nu Bgd After Cuts Nu Bgd Surviving bgd different for different Nhit showers  New Analysis Paradigm (VT)  Apply progressively less tight cuts for larger Nhit  Increased detection Efficiency and lower bgd R.S.Raghavan/VT/June05

Analysis Strategies: Basic selection: Events with given Nhit Every hit in candidate event is a possible vertex with a previous beta in that cell to mimic nu event NEW ANALYSIS STRATEGY Classify events according to NHit Optimize cut conditions separately for each class R.S.Raghavan/VT/June05

Mass for 2000 ev/5y (pp flux3%) T (In) Bgd Rate /T In/y Nu Rate /T In/y Det Eff % p/MeV 6x6x pe/ MeV 5x5x p e/MeV 4x4x4 Cell Size ( mm x mm x mm ) S/N T (InLS) Typical LENS-Sol: DESIGN FIGS. OF MERIT (Lattice Design) 4mx4mx4m supermodules: InLS: 8% In; L(1/e) =1000cm; Y= 9000hν/MeV; R.S.Raghavan/VT/June05 g2 g2+g3 Shower Rad. R.S.Raghavan/VT/June05

Summary Major breakthroughs in In LS technoloy Detector Design Analysis and Background Simulations  Conceptual feasibility of In-based LENS secure Simple Small ( < 10 t In /125 ton InLS) LENS in view Next Steps—Work in Progress Chemical Technology of large scale InLS production Detector construction technology R.S.Raghavan/VT/June05

VT-NRL Low Bgd Kimballton Mine VA