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Active-Sterile Neutrino Oscillations in LENS C. Grieb, J. Link and R. S. Raghavan Virginia Tech

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?

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Active-Sterile Neutrino Oscillations in LENS C. Grieb, J. Link and R. S. Raghavan Virginia Tech

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

  2. 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

  3. 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 ?

  4. LENS-Sol / LENS-Cal Collaboration (Russia-US: 2004-) Russia 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,

  5. Tagged ν –capture reaction in Indium LENS is the only developed CC real time detector for solar neutrinos signal delay Tag cascade • 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

  6. 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

  7. Major Progress --LENS • < Towards Hi Precision pp > • Hi Quality InLS Developed • Background Analysis Insights • New Detector Design Invented Transparency of InLS 8.6 m after 8 months

  8. Indium --Background Structure – Space / Time coincidence β1 (Emax< 2 keV) (b = 1.2x10-6)* E() -114 keV 115In =4.76s 115In e/ 116 keV β0 + n (BS) (Emax = 499 keV)  498 keV  497 keV 115Sn 115Sn *Cattadori et al: 2003 Signal Signal Signature: Prompt e- ( )followed by low energy (e-/) ( ) and Compton-scattered  ( ) ->time/space coincidence -> tag fixed energy 613keV ->compton scattered shower 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).

  9. Signal and Indium-Background Rates • Signal / Background ~3 with pp- event detection efficiency 64% • Remember: only pp- events affected by Indium Background, 7Be, pep and CNO Background-free

  10. 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

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

  12. Long Term Stability of L1/e of InLS • 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

  13. New Detector Concept - The Scintillation Lattice Chamber Test of transparent double foil mirror in liq. @~2bar Light propagation in GEANT4 Concept 3D Digital Localizabilityof 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

  14. 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 Upper limit ~1700pe/MeV (L=10m) - reach via antireflective coating on films? Adopt 1020 pe/MeV 7.5 cm cells Photoelectron yield versus number of cells: 4x4x4m Cube Absorption length = 10m

  15. 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

  16. 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

  17. LS Envelope InLS InLS 500 mm 500 mm Opt segmentation cage Passive Passive Mirror Mirror 5 5 ” ” PMT PMT Shield Shield MINILENS Final Test detector for LENS • 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

  18. Table I: Characteristics of neutrino Sources for LENS-CAL Neutrino Energy typically 700 keV

  19. 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

  20. 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

  21. 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 shortbase lines ~30m! Implies Δm2 ~ 1 eV2

  22. 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

  23. Statistical precision of oscillation parameter measurement in LENS

  24. Gail Maclaughlin (Private Comm.)

  25. 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

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