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SAGE: status and future

SAGE: status and future. V.N. Gavrin Institute for Nuclear Research of the Russian Academy of Sciences , Moscow. Outline Introduction and a little history SAGE Source experiments Comparison of Ga result to prediction SSM Is the neutrino capture rate in Ga constant?

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SAGE: status and future

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  1. SAGE: status and future V.N. Gavrin Institute for Nuclear Research of the Russian Academy of Sciences, Moscow

  2. Outline • Introduction and a little history • SAGE • Source experiments • Comparison of Ga result to prediction SSM • Is the neutrino capture rate in Ga constant? • Future

  3. νe, CC, NCSNO (5 MeV) 0,90 ± 0,08 νe SuperK (5 MeV) 0,406 ± 0,04 71Ga + νe71Ge + e- Ga-Ge (0,23 MeV)0,52 ± 0,03 νe Kamiokande II (7,5 MeV)0,48 ± 0,08 37Cl + νe37Ar + e-Cl-Ar (0,81 MeV) 0,30 ± 0,03

  4. 71Ga + νe71Ge + e- T1/2 = 11,43 d SAGE Baksan Neutrino Observatory, northern Caucasus, 3.5 km from entrance of horizontal adit, 2100 m depth (4700 m.w.e.) Data taking: Jan 1990 - till present, 50 tons of metallic Ga. Atoms of 71Ge chemical are extracted and its decay is counted. Sensitivity: One 71Ge atom from 5·1029 atoms Ga with efficiency ~90% B - Gallium-Germanium Neutrino Telescope

  5. SAGE Measurement of the solar neutrino capture rate with gallium metal.71Ga(v, e-)71Ge, Eth = 0.233 keV Presently SAGE is the only experiment sensitive to the ppneutrinos It is one of the longestalmostuninterrupted time of measurements among solar neutrino experiments 17 year period (1990 – 2006): 157 runs, 288 separate counting sets Results: 66.2+3.3-3.2+3.5-3.2 SNU or 66.2+4.8-4.5 SNU All extractions as function of time Combined results for each year 64+24/-22 SNU SAGE continues to perform regular solar neutrino extractions every four weeks with ~50 t of Ga

  6. GALLEX (05.91-01.97, 65 runs) → 77.5 ± 7.7 SNU GNO (05.98 – 09.03, 58 runs) → 62.9 ± 5.9 SNU GALLEX + GNO (123 runs) → 69.3 ± 5.5 SNU SAGE + GALLEX + GNO → 67.6 ± 3.7 SNU SAGE (45 runs) →79.4 ±9.4 SNU SAGE (49 runs) →65.0 ±6.0 SAGE (01.90 – 12.06, 157 runs) → 66.2 ± 4.6 SNU

  7. Source experiments

  8. GALLEX Cr-1 1.00+0.11-0.10 SAGE Cr 0.95 ± 0.12 GALLEX Cr-2 0.81 ± 0.10 SAGE Ar 0.79+0.09-0.10 51Cr 37Ar Gallium chloride solution Gallium metal (SAGE) (GALLEX) (1) (2) mGa (tons) 30.4 30.4 13.1 13.1 mof target (kg) 35,5 35,5 0,513 330 enrichment (% 50Cr) 38,6 38,6 92,4 96,94% 40Ca (natural Ca) source specific activity (KCi/g) 0,048 0,052 1,01 92,7 source activity (MCi) 1,71 1,87 0,52 0,41 expected rate 11,7 12,7 14,0 13,9 R = pmeasured/ppredicted 1.0±0.11 0.81±0.10 0.95±0.12 0.79±0.1 Weighted average 0.88±0.05 Rcombined 0.90±0.07 0.86±0.08

  9. V. Kuzmin, 1965 W. Haxton, 1988

  10. The source experiments with Ga * The weighted average value of Ris 0.88 ± 0.05,more thantwo SD less than unity. * If the contribution of these two excited states to the predicted rate is set to zero, then R = 0.93 ± 0.05, reasonably consistent with unity. * We believe that, although not statistically conclusive, the combination of these experiments suggests that the predicted rates is overestimated. The most likely hypothesis is that the cross sections for neutrino capture to the lowest two states in 71Ge, both of which can be reached using either 51Cr or 37Ar sources, have overestimated. * A new experiment with a considerably higher rate from the neutrino source is planned now to settle this question.

  11. 51Cr 37Ar Gallium chloride solution Gallium metal (SAGE) (GALLEX) (1) (2) mGa (tons) 30.4 30.4 13.1 13.1 mof target (kg) 35,5 35,5 0,513 330 enrichment (% 50Cr) 38,6 38,6 92,4 96,94% 40Ca (natural Ca) source specific activity (KCi/g) 0,048 0,052 1,01 92,7 source activity (MCi) 1,71 1,87 0,52 0,41 expected rate 11,7 12,7 14,0 13,9 R = pmeasured/ppredicted 1.0±0.11 0.90±0.09 0.95±0.12 0.79±0.1 Rcombined 0.94±0.07 0.86±0.08

  12. Without contributions from the first two excited states 0.95±0.05 GALLEX 71As experiment! Weighted average Including contributions from the first two excited states 0.90±0.05 R = pmeasured/ppredicted 1.0±0.11 0.90±0.09 0.95±0.12 0.79±0.1 Rcombined 0.94±0.07 0.86±0.08

  13. Reactor SM Cross-section Research Institute of Atomic Reactors Beryllium Reflector Thermal neutron flux – (1.08-3.44) x 1014сm-2sec-1 30 Irradiation Cells 28 Fuel Assemblies Special Fuel Assembly Thermal neutron flux – 1.66 x 1015сm-2sec-1 Central Neutron Trap 2 Automatic Shim Rods 4 Shim Rods with Additional Fuel Assembly

  14. Dependence of 51Сrspecific activityon time of irradiation Density of thermal neutron flux (сm-2sec-1): 1 - 1,5 x 1015; 2 - 1,0 x 1015;3 - 5,0 x 1014; 4 - 1,0 x 1014

  15. Comparison of gallium result to predictions standard of solar model

  16. Table of factors needed to compute the capture rate in 71Ga solar neutrino experiments calculated by B.T.Cleveland. *The units offlux are1010(pp), 109(7Be), 108(pep, 13N,15O), 106(8B,17F), 103(hep) cm-2s-1. The uncertaintyvalues are at 68% confidence. SAGE + GALLEX + GNO → 67.6 ± 3.7 SNU Excellent agreement * http://arXiv.org/abs/nucl-ex/0703012

  17. THE pp NEUTRINO FLUX [pp+7Be+CNO+pep+8B|Ga] =67.6 ± 3.6 SNU from 288 solar neutrino extractionsin the SAGE andGALLEX/GNO experiments [8B|SNO] = (1.68 ± 0.11) ×106νe/(cm2s-1) → [8B|Ga] = 3.7 +1.2-0.7 SNU [pp+7Be+CNO+pep|Ga] = 64.0+3.7-3.3 SNU [7Be+CNO+pep+8B|Cl] = 2.56 ± 0.23 SNU [8B|Cl] = 1.72 ± 0.14 SNU→ [7Be+CNO+pep|Cl] = 0.84 ± 0.27 SNU [7Be+CNO+pep|Ga] = [7Be+CNO+pep|Cl] × =23.9+7.9-7.6 SNU [7Be+CNO+pep|Ga] = 23.9+8.1-8.0 SNU [pp|Ga] = [pp+7Be+CNO+pep|Ga] - [7Be+CNO+pep|Ga] = 40.1+6.6-9.0 SNU → the measured electron neutrinoppflux at Earth of (3.41+0.76-0.77)× 1010/(cm2s-1) (5.94 ± 0.06) × 1010/(cm2s-1) (SSM) ×( )= (3.30 +013-0.14)× 1010/(cm2s-1) Excellent agreement

  18. Is the neutrino capture rate in Ga constant?

  19. Δ~ 2σ

  20. If one assumes the rate in Gallex-GNO varies linearly in time then the best fit gives [Capture rate = 82 ± 10 - (1.7 ± 1.1) × [t(year) - 1990] Altmann M et al. 2005 Phys Lett B 616] time variationχ2/dof prob χ2/dof prob with 10.8/5 5.6% 11.7/16 76% without 13.2/6 4.0% 11.4/17 83% At the present time we cannot differentiate between these two hypotheses, but it should become possible to do so with additional data.

  21. Future • Further running for the next three years. • Measurement of the response of a Ga solar neutrino experiment to neutrinos from a 51Cr source with accuracy better than 5%.

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