Active-Sterile Neutrino Oscillations in LENS C. Grieb, J. Link and R. S. Raghavan Virginia Tech XII Neutrino Telescopes Venice, March 8 2007

LENS is a high-resolution, real time spectrometer for low energy solar neutrinos such as pp, Be etc Why LENS for active-sterile oscillations? Novel Technology brings unique tools in play for short baseline disappearance experiments using monoenergetic e-flavor neutrinos from a radioactive source Parasitic measurement to solar neutrino program—sterile neutrinos are free! Sensitivity highest, well beyond Miniboone projected - new physics and astrophysics irrespective of LSND and Miniboone result

Two part Talk I LENS overview- Properties relevant to short baseline oscillations II How to make a sensitive search for active-sterile oscillations in LENS ?

LENS-Sol / LENS-Cal Collaboration (Russia-US: 2004-) INR (Moscow): I. Barabanov, L. Bezrukov, V. Gurentsov, V. Kornoukhov, E. Yanovich IPC (Moscow): N. Danilov, G. Kostikova, Y. Krylov INR (Troitsk) I: J. Abdurashitov, V. Gavrin. et al. II: V. Betukhov, A. Kopylov, I. Oriachov, E.Solomontin U. S.: BNL: R. L. Hahn, M. Yeh UNC: A. Champagne ORNL: J. Blackmon, C. Rasco, Qinlin Zeng, A. Galindo- Uribarri Princeton U. : J. Benziger SCSU: Z. Chang Virginia Tech: C. Grieb, J. Link, M. Pitt, R.S. Raghavan, R. B. Vogelaar, LENS-Sol / LENS-Cal Collaboration (Russia-US: 2004-)

LENS is the only developed CC real time detector for solar neutrinos Tagged ν –capture reaction in Indium LENS is the only developed CC real time detector for solar neutrinos Unique: Specifies ν Energy Eν = Ee + Q Complete LE nu spectrum Lowest Q known 114 keV access to 95.5% pp nu’s Target isotopic abundance ~96% Powerful delayed coinc. Tag Can suppress bgd =1011 x signal Downside: Bgd from 115In radioactivity to ( pp nu’s only) rate= 1011 x signal Tools: Time & Space coinc. Granularity (106suppression) Energy Resolution In betas <500 keV; ∑Tag = 613 keV 3. Other analysis cuts signal delay Tag cascade

Expected Result from LENS Background precisely and concurrently measured Well resolved low energy solar nu spectrum –  pp, 7Be, pep, CNO with 99+% of solar nu flux Solar luminosity in nu’s pp spectral shape accessible for first time

Light attenutation L(1/e) Major Progress --LENS < Towards Hi Precision pp > Hi Quality InLS Developed Background Analysis Insights New Detector Design Invented 8.6 m after 8 months Transparency of InLS   Status Design of Detector Cubic Lattice Chamber Composition InLS PC based: In content Light attenutation L(1/e) Signal Eff Pe/MeV NEW : LAB based- Similar as in PC >8% >10m 900 Indium Mass(1900 pp/5y) 10 ton Total Mass 125 ton PMT’s 13,300 Neutrino detection eff. 64% (pp) >85% all other S/N (β+γ (All In decay modes) ~3 (pp) >> 3 (ALL OTHER)

Indium --Background Structure – Space / Time coincidence Signal Signal Signature: Prompt e- ( )followed by low energy (e-/) ( ) and Compton-scattered  ( ) ->time/space coincidence -> tag fixed energy 613keV ->compton scattered shower E() -114 keV 116 keV 497 keV 115In 115Sn e/  =4.76s 115In β0 + n (BS) (Emax = 499 keV) 498 keV *Cattadori et al: 2003 β1 (Emax< 2 keV) (b = 1.2x10-6)* 115Sn  Background: Random time and space coincidence between two -decays ( ); Extended shower ( ) can be created by: a) 498 keV  from decay to excited state; b) Bremsstrahlungs -rays created by ; c) Random coincidence (~10 ns) of more -decays; Or any combination of a), b) and c).

Signal and Indium-Background Rates pp Signal /y /t In Bgd tot Bgd A1 Bgd A2 Bgd B Bgd C RAW 62.5 79 x 1011 Valid tag (Energy, Branching, Shower) in Space/Time delayed coinc. with prompt event in vertex 55 2.76 x 105 8.3 x 104 2.8 x 103 1.9 x 105 43.9 + ≥3 Hits in tag shower 49.5 6.23 x 104 5.81 x 104 2.76 x 103 1.4 x 103 43.7 +Tag Energy = 613 keV 44.4 458 0.48 5.2 445 8.0 +Shower Radius 270 5.1 264 0.73 +Hit Separation 40.2 13.3 ±0.6 4.7 8.1 0.004 Signal / Background ~3 with pp- event detection efficiency 64% Remember: only pp- events affected by Indium Background, 7Be, pep and CNO Background-free

Technology Indium Liquid Scintillator Chemistry Robust LENS-Grade Properties Demonstrated in Lab Scale Large Scale Production Next Detector Design Novel Scintillation Lattice Invented Optical properties simulated and analyzed for optimal Design Prototypes in development

Indium Liquid Scintillator Status 1. Indium concentration ~8%wt (higher may be viable) 2. Scintillation signal efficiency (working value): 9000 h/MeV 3. Transparency at 430 nm: L(1/e) (working value): 10m 4. Chemical and Optical Stability: at least 1 year 5. InLS Chemistry - Robust Basic Bell Labs Patent, Chandross & RSR. 2004 8% InLS (PC:PBD/MSB) 10800 hν / MeV BC505 Std 12000 h/MeV In 8%-photo Light Yield from Compton edges of 137Cs -ray Spectra l (nm) Norm. Absorbance in 10 cm L(1/e)(InLS 8%) ~ L(PC Neat) ! ZVT39: Abs/10cm ~0.001;  L(1/e)(nominally) >>20 m InLS PC Neat Indium Liquid Scintillator Status Milestones unprecedented in metal LS technology LS technique relevant to many other applications

Long Term Stability of L1/e of InLS Abs@430nm at different time Sample pH In% S% Abs@430nm at different time Begin 1 Mon 3 Mon 5 Mon 8 Mon 9 Mon zVt39 7.24 8.7 64 0.001 0.002 0.003 0.009 0.012 0.013 zVt40 7.22 8.4 63 0.005 0.006 0.010 -- zVt41 7.09 59  -- --   0.008 zVt46 6.98 8.5 58  0.007 0.008 zVt38 6.94 8.3 61 0.007 zVt47 6.92 8.0 0.0025 zVt45 6.88 8.2 56 0.004 zVt44 6.86 8.6 0.004   0.004 The S values of the samples were found not to change with time. The L1/e of the samples synthesized at pH 6.88 were found to stabilize in 3 months, and their L1/e have stayed > 8 m for 8 months. Optimum value for the extraction pH ~6.88

The Scintillation Lattice Chamber New Detector Concept - The Scintillation Lattice Chamber Light propagation in GEANT4 Concept Test of transparent double foil mirror in liq. @~2bar 3D Digital Localizability of Hit within one cube  ~75mm precision vs. 600 mm (±2σ) by TOF in longitudinal modules  x8 less vertex vol.  x8 less random coinc.  Big effect on Background  Hit localizability independent of event energy

Light loss by Multiple Fresnel Reflection A small part of light crossing a gap is reflected back and undergoes multiple reflections, thus, suffers extra bulk absorption in the liquid Photoelectron yield versus number of cells: Upper limit ~1700pe/MeV (L=10m) - reach via antireflective coating on films? Adopt 1020 pe/MeV 7.5 cm cells 4x4x4m Cube Absorption length = 10m

Real life issue--Foil Surface Roughness and Impact on the Hit Definition 100 keV event in 4x4x4m cube, 12.5cm cells Perfect optical surfaces : 20 pe (per channel) Rough optical surfaces : 20% chance of non- ideal optics at every reflection 12 pe in vertex + ~8 pe in “halo” Conclusion - Effect of non-smooth segmentation foils: No light loss - (All photons in hit and halo counted) Hit localization accuracy virtually unaffected

Can we get away with a single foil optical structure-? “Hard Lattice” No trapped air Easier construction More robust Most photons still “channeled” crit~60 Still Good event localization Less trapping Greater light output Solid Teflon Segmentation Challenges: How to deal with “spray”? Background rate Trigger logic

MINILENS InLS LS Envelope 500 mm Mirror Final Test detector for LENS 5 ” PMT Passive Shield Mirror Opt segmentation cage InLS 500 mm LS Envelope Goals for MINILENS Test detector technology  Medium Scale InLS production  Design and construction Test background suppression of In radiations by 10-11  Expect ~ 5 kHz In -decay singles rate; adequate to test trigger design, DAQ, and background suppression schemes Demonstrate In solar signal detection in the presence of high background (via “proxy”) Direct blue print for full scale LENS

Table I: Characteristics of neutrino Sources for LENS-CAL DecayMode /Produced by t En (keV) Ee= En-0.114 keV Background 37Ar Haxton EC/ (n, a) 50.5 d 814(100%) 700 Int. Bremms. 0-814; ~S5x10-4 hn/decay 51Cr RSR Kuzmin EC/ (n,g) 40.1 d 751 (90%) 637 320g (10%) Imp. g’s (MeV) %?? 65Zn Louis Alvarez EC(b+)/ (n,g) 353 d 1350 (50%) 1236 1115 g (50%); 511 g (2%); Imp. g’s. Neutrino Energy typically 700 keV

Sterile neutrino tests in LENS Unique advantages Put strong articial Neutrino Source into LENS Pure, e-flavor, monochromatic neutrino line Measure Pee as function of Distance—Disappearance Measurement 3-D location allows measurement of RADIAL dependence of Pee All systematic, normalization and spectral peeling errors endemic in broad beam reactor spectra drop out Measure Pee (r) with100,000 detectors, not just 2 or 3

LENS OFFERS UNIQUE TEST For Sterile Neutrinos Already planned: LENS Cal MCi Cr Source in LENS Calibrate In X-section Parasitic measurement For sterile neutrinos Active Sterile Osc of mono- Chromatic 753 keV pure e-flavored neutrinos Via Spatial distribution of Flavor Survival in ~5 m Active-Sterile Oscillations

Sterile Neutrinos—( Neutrinos of the wrong helicity) Physics well beyond the Standard Model --Fourth (Fifh) mass state with high mass splitting triggered by LSND Appearance of e flavor from μ beams at short base lines ~30m! Implies Δm2 ~ 1 eV2

Pee = 1 − s2 (e4) s2 (41) – s2 (e5) s2( 51) where cross terms such as s2 (e4)s2 (e5) are neglected. In (2) the mixing terms s2( en) = sin2 2θen = [4U2 (en) (1-U2(en)] and the frequencies s2 n1 = sin2 [(1.27Δm(n1)2 eV2 ) x L(m)/Eν(MeV)) . The values of s(en) and Δm2 are from Ref 4 (Table 1). With Δm2 = 1 eV2 and Eν ~0.753 MeV (from 51Cr), (2) full flavor recovery occurs in ~2m, directly observable in a lab-scale detector

Statistical precision of oscillation parameter measurement in LENS

Gail Maclaughlin (Private Comm.)

Conclusions LENS offers a new and sensitive tool for searching for active-sterile nu oscillations The advanced sensitivity allows the search in its own right towards new physics and astrophysics Independent of LSND or Miniboone results Parasitic measurement—No extra resources needed