Measuring the Neutrino Luminosity of the Sun & Search for Sterile Neutrinos LENS & MINILENS International Workshop on "Double Beta Decay and Neutrinos" Osaka, June 12, 2007 Christian Grieb for the LENS Collaboration Virginia Tech
LENS-Indium: Foundations CC ν ν -capture in 115 In to excited isomeric level in 115 Sn ν ν 115 ( / ) 115 ν + → − + γ + γ − + In e e Sn � e � � � � � solar signal delayed tag ( 4.76 s) τ = µ Tag: Delayed emission of (e/ γ )+ γ Threshold: 114 keV � pp- ν ’s 115 In abundance: ~ 96% CC-capture: Faithful reproduction of ν spectrum Background Challenge: • Indium-target is radioactive! (t = 6x10 14 y) • 115 In β -spectrum overlaps pp- ν signal Basic background discriminator: Time/space coincidence tag Tag energy: E ν -tag = E β max +116 keV Requires spatial resolution of < 10cm 7 Be, CNO & LENS-Cal signals not affected by Indium-Bgd! LENS Christian Grieb, Virginia Tech, June 2007
Indium β - -Background Structure – Space / Time coincidence Signal Signal Signature: E( ν ν ν ν ) -114 keV Prompt e - ( ) τ τ =4.76 µ τ τ µ s µ µ 115 In followed by e/ γ γ γ γ 116 keV low energy (e - / γ ) ( ) and Compton-scattered γ ( ) γ γ γ γ 497 keV -> time/space coincidence -> tag fixed energy 613keV ->compton scattered shower 115 Sn Background: β 1 (E max < 2 keV) 115 In (b = 1.2x10 -6 )* Random time and space coincidence between two β -decays ( ); Extended shower ( ) can be created by: β 0 + n γ γ (BS) γ γ γ γ γ γ 498 keV γ from decay to excited 498 keV a) (E max = 499 keV) state; Bremsstrahlungs γ -rays created by β ; b) c) Random coincidence (~10 ns) of 115 Sn more β -decays; *Cattadori et al: 2003 Or any combination of a), b) and c). Background LENS Christian Grieb, Virginia Tech, June 2007
New Detector Technology - The Scintillation Lattice Chamber Test of double foil Light propagation Concept mirror in liq. @~2bar in GEANT4 3D Digital Localizability of Hit within one cube � ~75mm precision vs. 600 mm ( ± 2 σ ) by TOF in longitudinal modules � x8 less vertex vol. � x8 less random coinc. � Big effect on Background � Hit localizability independent of event energy LENS Christian Grieb, Virginia Tech, June 2007
In-Background Rejection N year -1 t In -1 keV -1 Total Energy deposition in Tag A1 Bkgd Background rejection steps: A2 Bkgd pp- ν Events 1. Time/space coincidence in the same B Bkgd C Bkgd cell required for trigger; D Bkgd 2. Tag requires at least three ‘hits’; 3. Narrow energy cut; 4. Tag topology: multi- β vs. Compton shower; Classification of events according to hit E tag [keV] multiplicity; Cut parameters optimized for each event class improved efficiency; N year -1 t In -1 2keV -1 Total Energy Black: pp- ν events deposition β 1 (E max < 2 keV) Blue: A1 Bgd 115 In in Tag (b = 1.2x10 -6 )* Green: A2 Bkgd Red: B Bkgd β 0 + n γ γ γ (BS) γ γ γ γ γ 498 keV (E max = 499 keV) 115 Sn E tag [keV] *Cattadori et al: 2003 LENS Christian Grieb, Virginia Tech, June 2007
Indium β β β β - -Background Rejection - MC Results Results of GEANT4 Monte Carlo simulation (cell size = 7.5cm) Reduction Signal (pp) Bgd (In) y -1 t In) -1 by ~3 . 10 7 y -1 (t In) -1 through RAW rate 62.5 79 x 10 11 time/space coincidence A. Tag in Space/Time delayed coincidence 50 2.76 x 10 5 with prompt event in vertex B. + ≥ ≥ 3 Hits in tag shower ≥ ≥ 2.96 x 10 4 46 C. +Tag Energy = 613 keV 44 306 13 ± ± 0.6 ± ± D. +Tag topology 40 � Signal / Background ~3 with pp- ν event detection efficiency 64% � Remember: only pp- ν events affected by Indium Background, 7 Be, pep and CNO Background-free � LENS is a feasible detector: 125t of liquid scintillator for ~2000 pp- ν events in 5 years with full spectroscopic information plus 7 Be, pep and CNO LENS Christian Grieb, Virginia Tech, June 2007
Indium Liquid Scintillator Status BC505 Std 8% InLS (PC:PBD/MSB) 12000 h ν ν /MeV ν ν 10800 h ν / MeV Milestones unprecedented 10000 in metal LS technology 1000 LS technique relevant to 100 many other applications In 8%-photo 10 Light Yield from Compton edges of 137 Cs γ γ γ -ray Spectra γ 1. Indium concentration ~8%wt 1 (higher may be viable) 0 50 100 150 200 250 2. Scintillation signal efficiency 0.030 (working value): 9000 h ν /MeV L(1/ e )(InLS 8%) ~ L(PC Neat) ! Norm. Absorbance in 10 cm 0.025 3. Transparency at 430 nm: ZVT39: Abs/10cm ~0.001; L(1/ e ) (working value): 10m 0.020 � L(1/e)(nominally) >>20 m � � � 0.015 4. Chemical and Optical 0.010 Stability: at least 1 year InLS 0.005 5. InLS Chemistry - Robust 0.000 PC Neat -0.005 Basic Bell Labs Patent, 350 390 430 470 510 550 590 630 670 λ (nm) λ λ λ filed 2001, awarded 2004 LENS Christian Grieb, Virginia Tech, June 2007
LENS Expected Result: Low Energy Solar ν ν ν -Spectrum ν >98% Flux <2MeV Signal ( τ τ τ = 4.76 µs) τ LENS-Sol Signal = SSM(low CNO) + LMA x Detection Efficiency ε ε ε ε ε ε ε ε = 64% pp: 7 Be: ε ε ε = 85% ε pep: ε ε ε ε = 90% � Rate: pp 40 pp ev. /y /t In � 2000 pp ev./ 5y/10t In � � � � ± ± 2.5% ± ± � Design Specification: S/N ≥ ≥ 3 ≥ ≥ Access to pp ν ν ν ν spectral shape for the first time LENS Christian Grieb, Virginia Tech, June 2007
Solar Luminosity: Neutrino vs. photon Energy Balance: Measured neutrino fluxes at earth Solar luminosity L ? L + oscillation physics as measured inferred = ν − ν h nuclear reaction rates by photon flux energy release in the sun Will be met under these conditions: 1. Fusion reactions are the sole source of energy production in the sun 2. The sun is in a quasi-steady state (change in 40,000 years is negligible) 3. The neutrino oscillation model is correct & no other physics involved; From a single detector: Test of astrophysics, solar model; Test of neutrino physics (LMA-MSW at low E, NSI, mass-varying ν s, Θ 13, …); LENS Christian Grieb, Virginia Tech, June 2007
Neutrino inferred Luminosity of the Sun - Experimental Status Predicted relative neutrino fluxes at the sun (SSM): Main contributions: pp 0.91 7 Be 0.074 (CNO 0.014) Measured neutrino fluxes at the earth: 8 B 0.00009 8 B (SK, SNO) known very well 7 Be + 8 B (Cl) sensitive mostly to 8 B pp + 7 Be + 8 B (Ga) 7 Be (Borexino, Kamland – in the future) � in principle can deduce pp- ν flux Problem : disentangling fluxes from individual neutrino sources ( ) ( ) σ ( ) / 1 . 2 0 . 2 = / 1 . 4 0 . 2 0 . 7 = L L L L (inferred) ν ν h ν (inferred) ν 0 . 3 0 . 6 h 1 3 σ R.G.H.Robertson, Prog. Part. Nucl. Phys. 57 , 90 (2006) J.N.Bahcall and C.Peña-Garay, JHEP 0311 , 4 (2003) Experimental status – No useful constraint! LENS Christian Grieb, Virginia Tech, June 2007
Probing the Temperature Profile of Energy Production in the Sun with LENS Neutrino Production Temperature Profile J. N. Bahcall and R. Ulrich, Rev. Mod. Phys. 60 , No. 2, p. 297 (1988) J. N. Bahcall and R. Ulrich, Rev. Mod. Phys. 60 , No. 2, p. 297 (1988) LENS Christian Grieb, Virginia Tech, June 2007
Temperature in the Solar Core impacts Neutrino Energies, not just relative fluxes Relative kinetic particle energies pp- and pep neutrino production temperature add to the Q-value of capture and and related Gamow peak energy: fusion reactions. Not all energies contribute evenly: pep pp-fusion: = 5 . 91 ⋅ 2 E keV T E 0 3 Gamow Peak at 0 15 5 . 91 ( / 1 . 5 10 7 ) 2 = ⋅ ⋅ E keV T K 3 0 pp Maxwellian energy distribution X Tunneling probability 7 Be electron capture: maxwellian energy distribution shifts mean energy of 7 Be ν line by ∆ <E> ~ 1.29 keV pp endpoint shifted up by ~5.2keV J.N. Bahcall, Phys. Rev. D 49 (8), 3923 (1994) J.N. Bahcall, Phys. Rev. D 44 (6), 1644(1991) 10 . 73 ( / 1 . 5 10 7 ) 2 = ⋅ ⋅ E keV T K pep: combination, delta ∆ <E> ~ 6.6 keV 3 hep: 0 J.N. Bahcall, Phys. Rev. D 44 (6), 1644(1991) LENS Christian Grieb, Virginia Tech, June 2007
Probing the Temperature Profile of Energy Production in the Sun with LENS Top:pp- ν spectrum with/without Gamow shift Bottom: Signal spectrum in LENS with/without Measured Gamow shift Gamow shift in improved LENS: 12t Indium - 6years 10000 simulations with - δ E/E=6% at ~3000 pp ν events each 300keV σ =1.62keV C. Grieb and R.S. Raghavan, Phys.Rev.Lett.98:141102,2007 Conclusion: Slightly improved LENS can detect the predicted Gamow shift in the pp- ν endpoint ∆ E=5.2keV with 95% confidence. LENS Christian Grieb, Virginia Tech, June 2007
LENS-Cal Neutrino Sources τ τ τ τ ν ( ( keV) ( ( Source DecayMode E ν E e = Background ν ν ν − − 0.114 keV − − /Produced E ν ν ν by EC/ (n, α) α) α) α) 37 Ar 50.5 d 814(100%) 700 Int. Bremss. 0-814; ~ Σ Σ 5x10 -4 h ν Σ Σ ν /decay ν ν Haxton EC/ (n, γ γ γ ) γ 320 γ γ γ (10%) γ 51 Cr 40.1 d 751 (90%) 637 Imp. γ γ ’s (MeV) %?? γ γ RSR Kuzmin EC( β β + )/ 1115 γ (50%); γ (50%); 511 γ γ (2%); β β γ (50%); γ (50%); γ γ 65 Zn 353 d 1350 (50%) 1236 (n, γ γ γ γ ) Imp. γ γ ’s. γ γ Louis Alvarez Neutrino Energy typically 700 keV LENS Christian Grieb, Virginia Tech, June 2007
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