V.N. Gavrin Institute for Nuclear Research of the Russian Academy of Sciences , Moscow

1. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin Opportunities of SAGE with artificial neutrino source for investigation of active-sterile transitions V.N. Gavrin Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 15-th Lomonosov Conference on Elementary Particle Physics, August 18-24, Moscow

2. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin SAGE Baksan, Russia GALLEX/GNO Gran Sasso, Italy 71Ga(ve, e-)71Ge Eth = 233 keV 50 tons of metallic natural Ga 1990-2009, running 168 runs (Jan 1990 – Dec 2007) give the result:65.4+4.0-4.1SNU 30 tons of natural Ga (103 tons of GaCl3 acidic solution) 1991-2003 123 runs (May 1991 – Apr 2003) give the result: 67.5 ± 5.1 SNU The weighted average of the results of all Ga experiments is now 66.1±3.1 SNU

3. Gallium source experiments GALLEX r =25cm r = 5cm r=200cm r = 76cm h = 128cm h=500cm The experimental procedures of the SAGE and Gallex experiments,including the chemical extraction, counting, andanalysis techniques, have been checked by exposing the galliumtarget to reactor-produced neutrino sources SAGE SAGEhas used 51Cr and 37Ar R = pmeasured/ppredict = 0.87±0.05 Thetest ofSAGEwith the37Ar neutrino sourceindicates that SSMpredicted rate may be overestimated or electron neutrinos disappear due to a real physical effect of unknown origin. [PHYS. REV. C 73, 045805 (2006),PHYS. REV. C 80, 015807, (2009)] The unexpectedly low capture rate of neutrinos in Ga source experiments can be explained in frame of neutrino oscillations by assuming transitions from active to sterile neutrinos occur with Δm2 about 1eV2. This interpretation agrees with the results of a number of reactor and accelerator experiments. Gallex has twice used 51Cr

4. XV-th International School "PARTICLES and COSMOLOGY" May 26 - June 2 , 2011 Troitsk, Moscow Region, Russian Federation 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin BNO INR RAS V.N. Gavrin The cross sections for neutrino capture to the two lowest excited states in 71Ge have been overestimated (W. Haxton) Maximum contribution of these excited states – 5%. If the contribution of these states to the predicted rate were to be zero then R = 0.92 ± 0.06 and the fit to the expected value of 1.0 becomes quite reasonable (χ2 /dof = 4.58/3, GOF =21%). The measurements of (3He, t) reaction on Ga cross section were carried out in RCNP (Research Center for Nuclear Physics), Japan (H. Ejiri) last year. “ At RCNP we recently re-measured the GT transition strengths to various states in 71Ge with the main objective to extract the GT strength values to the g.s., the 175 keV and the 500 keV states with highest resolution and highest possible accuracy using the (3He,t) reaction at 420 MeV and the Grand Raiden spectrometer. …. one arrives at a value of6.9 ± 1.8% for the contribution from the excited states in 71Ge to the neutrino capture cross section.This is a slightly larger value than the one, which was roughly estimated by Bahcall and therefore slightly amplifies the discrepancy observed in the calibration measurements.” “… it may be worthwhile to review past measurements of the 71Ge EC Q-value and lifetime, which together define the final ft-value.” [TRIUMF Research Proposal]

5. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin TRIUMF Research Proposal Q-value measurement for the 71Ge electron capture Spokespersons : D. Frekers, J. Dilling, H. Ejiri We propose to measure the electron capture Q-value of 71Ge leading to the ground state of 71Ga using the TITAN(TRIUMF's Ion Trap for Atomic and Nuclear science) ion trap mass measurement facility. The exact mass difference is an important quantity, which enters into the neutrino cross section on 71Ga, and which needs to be known with high precision. 71Ga was the material, which was used in the solar neutrino experiments SAGE and GALLEX and subsequently for the detector calibration with neutrinos from a 51Cr calibration source. A renewed mass measurement using the ion trap technique will help to clarify the origin of a rather long-standing and still unresolved discrepancy of the calibration measurements performedby both neutrino experiments, SAGE and GALLEX. The TITAN Beamline

6. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin Region of allowed mixing parameters inferred from 4 gallium source experiments assuming oscillations to a sterile neutrino In Ga experiments:Eν~ 1 MeV L ~ 1 m Oscillations affect the capture rate withΔm2 ~ 1 eV2 Limits for oscillation parameters obtained in the four artificial neutrino source experiments: the best-fit point (plus) at Δm2=2.15эВ2 sin2(2θ)=0.24 χ2/dOf=1.77/2, GOF=41%

7. Neutrino Oscillation Observations Plot of all oscillation experiments: “Solar”:Δm2~10-5eV2, θ12 ~32° Confirmed! via reactor neutrinos “Atmospheric”: Δm2~10-3eV2, θ23 ~45° Confirmed! via accelerator neutrinos “High Δm2”: Δm2~1-10eV2 LSND and MiniBooNE observed excess ofνe in νμ beam Karmen, Bugeyexclude the parameter space - 4 Ga SOURCE EXP

8. The search for sterile neutrinos is now a field of most active investigation Accelerator experiments (NuMu- antiNuMu flux) MicroBooNE LArTPC detector designed to advance LAr R&D and determine whether the MiniBooNE low-energy excess is due to electrons or photons. Approximately 70-ton fiducial volume detector, located near MiniBooNE (Received Stage-1 approval at Fermilab and initial funding from DOE and NSF. May begin data taking as early as 2013. Currently, a 170LLAr TPC, called ArgoNeut, is taking data in the NuMI beam in front of the MINOS detector BooNEinvolves moving MiniBooNE or building a 2nd detector at a distance of ~200 m from the BNB target. With two detectors the systematic errors will be greatly reduced and will allow precision appearance and disappearance searches for neutrinos & antineutrinos OscSNS would involve building a “MiniBooNE-like” detector with higher PMT coverage at a distance of ~60 m from the Spallation Neutron Source (SNS) beam stop at ORNL which producesπ+s which decay at rest. Neutrino beam from the CERN-PS. Two strictly identical 600 ton liquid argon time projection chamber (LAr-TPC) in the ”near” and “far” positions, at 850 and 127 m from the target are simultaneously recorded in order to evidence possible oscillation effects. (The ICARUS T600 as “Far” detector and The additional T150 detector (to be constructed) Reactor neutrino experiments (antiNue) Double Chooz [14], Daya Bay Neutrino source experiments(Nue) SAGE,2-ZONE -(3MCi); BOREXINO, - (?);

9. 15-th Lomonosov conference on elementary particle physics Moscow, August 18-24, 2011 INR V.N. Gavrin • If sterile neutrino hints are accepted , then neutrino oscillations should be quantified in all channels: – νe andνe appearance – νμ andνμ disappearance – νe andνe disappearance • SAGE and Borexino experimentswith artificial neutrino source provide a unique opportunities to searches for very short baseline oscillations associatedwith: – νe disappearance(!)

10. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 BNO INR RAS V.N. Gavrin New Ga source experiment We propose to place a very intense source of 51Cr (3MCi) at the center of a 50-tonne target of gallium metal that is divided into two zones and to measure the neutrino capture rate in each zone. Production rate of 71Ge is p = D <L> A(atoms produced/day) D= ρ N0 f Mσ = 0.3906 (neutrino captures/cm day MCi)– all the physical factors: νinteraction cross section σ=5.8×10-45(1+0.028-0.036) cm2[Bahcall PRC.56, 1997], Ga density, etc. A = 3.2 × 1021 decays 51Cr /(day - MCi).source strength <L>– the average ν pathlength through the Ga. Monte Carlo integration using an accurate map of the vessel shape gives <L> ~55 ± 0.05 cm. Combining these factors gives an expected production rate at SOE:64.5 ± 0.09 atoms/day The experiment has the potential to test neutrino oscillation transitions with Δm2 > 0.5 eV2because: –compact source (several cm size), –nearly monochromatic neutrino source[~750keV (90%),~430keV(10%)], –with well-known activity (uncertainty can be as low as 0.5%) –dense Ga metal provides a high interaction rate, special target geometry makes it possible to study the dependence of the rate on the distance to the source. .

11. The MiniBooNE Detector (arXiv: 0806.4201) • 541 meters downstream of target • 3 meter overburden • 12.2 meter diameter sphere (10 meter “fiducial” volume) • Filled with 800 t of pure mineral oil (CH2) (Fiducial volume: 450 t) • 1280 inner phototubes (10% photocathode coverage), 240 veto phototubes • Simulated with a GEANT3 Monte Carlo

12. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin Sketch of two zone Ga experiment Target: 50 тGa metall Masses of the zones: 8 tand42t Path length in each zone: <L> = 55cm σ–cross sect.{5.8×10-45 cm2[Bahcall PRC.56, 1997] } sin2(2q) = 0.3

13. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin Expected results and uncertainty The 71Ge production rate from the source at the start of the first irradiation is expected to be ~ 65 atoms/day in each zone. Production rate from solar neutrinos is constant at 0.0197 atoms 71Ge/(d – 1ton Ga):(1.18 71Ge at. in 8 tonneof Ga and 6.20 71Ge at. in 42 tonneof Ga) 10 extractions each with 9 days irradiating by source with a dead time of 1 days (when the source is placed in the calorimeter) between the end of one irradiation and the beginning of the next irradiation . The total extraction and counting efficiency is ~ 0.53. The total systematic uncertainty is ±2.6 %. The total number of the events of 71Ge decays with statistical and systematical uncertainty is expected to be: 840 ± 3.7% (stat.) ± 2.6% (syst.) or 840 ± 4.5% atoms in each zone 1680 ± 2.6% (stat.) ± 2.6% (syst.) or 1680 ± 3.7% atoms for total target mass With the cross section uncertainty:5.5 % and 4.8%

14. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin BNO INR RAS V.N. Gavrin BNO INR RAS V.N. Gavrin Workshop on Emission Detectors Application and Neutrino Sources (National Research Nuclear University), MEPhI, 30 June – 1 July 2011 90% C.L., (1.65σ) 90% C.L., (1.65σ) 90% C.L., (1.65σ) 90% C.L., (1.65σ) 95% C.L., (1.96σ) 95% C.L., (1.96σ) 95% C.L., (1.96σ) 95% C.L., (1.96σ) 99% C.L., (2.58σ) 99% C.L., (2.58σ) 99% C.L., (2.58σ) 99% C.L., (2.58σ) Regions of allowed mixing parameters for various possible outcomes of new two-zone Ga experiment (R1,R2)=(1.0,0.80) (R1,R2)=(0.80,1.0) (R1,R2)=(0.90,0.75) (R1,R2)=(1.0,0.85)

15. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin BNO INR RAS V.N. Gavrin Exclusion curves & νe → νs- SAGE 2-zone exp

16. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin BNO INR RAS V.N. Gavrin Exclusion curves & νe → νs- SAGE 2-zone exp

17. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin BNO INR RAS V.N. Gavrin Exclusion curves & νe → νs- SAGE 2-zone exp

18. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin BNO INR RAS V.N. Gavrin Exclusion curves & νe → νs- SAGE 2-zone exp

19. 15-th Lomonosov Conference on Elementary Particle Physics Moscow, August 18-24, 2011 INR V.N. Gavrin The proposed Ga experimen thas several advantages: • independent measurements on two different baselines • nearly-monochromatic neutrino and the source with well-known activity • very compact source of pure νe flux • the dense target of Ga metal provides a high interaction rate and good statistical accuracy • all procedures are well understood and were used in the prior solar and source experiments • the absence of backgroundand uncertainties connected with inaccurate knowledge of neutrino spectrum will provide the simplicity of results interpretation The proposedexperiment has the potential to test neutrino oscillation transitionswith Δm2 > 0.5 eV2 The sensitivity to disappearance of electron neutrinos is expected to be a few percent

20. Reactor SM Cross-section Sketch of source Chromium rods

22. h = 55cm 44cm SAGE – GALLEX SAGE–…? W Cu W 517kCi 51Cr produced by irradiatin 512.7 g of 92.4%-enriched 50Cr in high-flux fast neutron breeder reactor BN-350 409kCi 37Ar produced by irradiatin 330 kg of CaO in the fast neutron breeder reactor BN-600 3MCi 51Cr 1994 –1995 2004 201? (1) 1.17 MCi 1994 –1995 (2) 1.87 MCi 1995 –1996

23. Waves with 51Cr source in WT(7m) BOREXINO From M-C 5000000 simulations, 3.3m FV, —NO oscillation. — for GALLEX source size(44 cm, h = 55cm) —for SAGE source size (8.6 cm, h = 9.5cm)

24. Vote for the Ga- BOREXINO source experiment!