SAGE status and future V N Gavrin Institute
- Slides: 21
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? • Future
νe, CC, NC SNO (5 Me. V) 0, 90 ± 0, 08 νe Super. K (5 Me. V) 0, 406 ± 0, 04 71 Ga + νe 71 Ge + e- Ga-Ge (0, 23 Me. V) 0, 52 ± 0, 03 Kamiokande II (7, 5 Me. V) 0, 48 ± 0, 08 νe 37 Cl + νe 37 Ar + e- Cl-Ar (0, 81 Me. V) 0, 30 ± 0, 03
71 Ga + ν 71 Ge + ee T 1/2 = 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 71 Ge chemical are extracted and its decay is counted. Sensitivity: One 71 Ge atom from 5· 1029 atoms Ga with efficiency ~90% B - Gallium-Germanium Neutrino Telescope
SAGE Measurement of the solar neutrino capture rate with gallium metal. 71 Ga(v, e-)71 Ge, E = 0. 233 ke. V th Presently SAGE is the only experiment sensitive to the pp neutrinos It is one of the longest almost uninterrupted 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
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 (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 SAGE + GALLEX + GNO → 67. 6 ± 3. 7 SNU
Source experiments
51 Cr GALLEX Cr-1 Gallium chloride solution Gallium metal 1. 00+0. 11 -0. 10 (GALLEX) SAGE Cr (1) (2) 0. 95 ± 0. 12 37 Ar (SAGE) m. Ga (tons) 30. 4 13. 1 mof target (kg) 35, 5 0, 513 330 Weighted 50 40 enrichment (% Cr) 38, 6 92, 4 96, 94% Ca (natural Ca) average source specific activity (KCi/g) 0, 048 0, 052 1, 01 92, 7 0. 88± 0. 05 GALLEX Cr-2 SAGE Ar source activity +0. 09 0. 79 -0. 10 (MCi) 1, 71 1, 87 0. 81 ± 0. 10 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 Rcombined 0. 90± 0. 07 0. 86± 0. 08
V. Kuzmin, 1965 W. Haxton, 1988
The source experiments with Ga * The weighted average value of R is 0. 88 ± 0. 05, more than two . 05 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 R = 0. 93 ± 0. 05 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 71 Ge, both of which can be reached using either 51 Cr or 37 Ar sources, have overestimated. * A new experiment with a considerably higher rate from the neutrino source is planned now to settle this question.
51 Cr Gallium chloride solution (GALLEX) (1) (2) Gallium metal 37 Ar (SAGE) m. Ga (tons) 30. 4 13. 1 mof target (kg) 35, 5 0, 513 330 50 Cr) enrichment (% 38, 6 92, 4 96, 94% 40 Ca (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
Without contributions from the first two excited states GALLEX 71 As experiment! Including contributions from the first two excited states 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 0. 95± 0. 05 Weighted average 0. 90± 0. 05
Reactor SM Research Institute of Atomic Reactors Cross-section Beryllium Reflector Thermal neutron flux – (1. 08 -3. 44) x 1014 сm-2 sec-1 30 Irradiation Cells 28 Fuel Assemblies Special Fuel Assembly Thermal neutron flux – 1. 66 x 1015 сm-2 sec-1 Central Neutron Trap 2 Automatic Shim Rods 4 Shim Rods with Additional Fuel Assembly
Dependence of 51 Сr specific activity on time of irradiation Density of thermal neutron flux (сm-2 sec-1): 1 - 1, 5 x 1015; 2 - 1, 0 x 1015; 3 - 5, 0 x 1014; 4 - 1, 0 x 1014
Comparison of gallium result to predictions standard of solar model
Table of factors needed to compute the capture rate in 71 Ga solar neutrino experiments calculated by B. T. Cleveland. * The units of flux are 1010 (pp), 109 (7 Be), 108 (pep, 13 N, 15 O), 106 (8 B, 17 F), 103 (hep) cm-2 s-1. The uncertainty values are at 68% confidence. SAGE + GALLEX + GNO → 67. 6 ± 3. 7 SNU Excellent agreement * http: //ar. Xiv. org/abs/nucl-ex/0703012
THE pp NEUTRINO FLUX [pp+7 Be+CNO+pep+8 B|Ga] = 67. 6 ± 3. 6 SNU from 288 solar neutrino extractions in the SAGE and GALLEX/GNO experiments [8 B|SNO] = (1. 68 ± 0. 11) × 106 νe/(cm 2 s-1) → [8 B|Ga] = 3. 7 +1. 2 -0. 7 SNU [pp+7 Be+CNO+pep|Ga] = 64. 0 +3. 7 -3. 3 SNU [7 Be+CNO+pep+8 B|Cl] = 2. 56 ± 0. 23 SNU [8 B|Cl] = 1. 72 ± 0. 14 SNU → [7 Be+CNO+pep|Cl] = 0. 84 ± 0. 27 SNU [7 Be+CNO+pep|Ga] = [7 Be+CNO+pep|Cl] × = 23. 9+7. 9 -7. 6 SNU [7 Be+CNO+pep|Ga] = 23. 9+8. 1 -8. 0 SNU [pp|Ga] = [pp+7 Be+CNO+pep|Ga] - [7 Be+CNO+pep|Ga] = 40. 1 +6. 6 -9. 0 SNU → the measured electron neutrino pp flux at Earth of (3. 41 +0. 76 -0. 77) × 1010/(cm 2 s-1) (5. 94 ± 0. 06) × 1010/(cm 2 s-1) (SSM) ×( ) = (3. 30 +013 -0. 14) × 1010/(cm 2 s-1) Excellent agreement
Is the neutrino capture rate in Ga constant?
Full data set 01/90 -12/06 Time period 05/14/91 -01/23/97 05/20/98 -04/09/03 05/14/91 - 4/09/03 Number runs 65 58 123 GALLEX/GNO 77. 5 ± 6. 2 +4. 3 -4. 7 62. 9 +5. 5 -5. 3 ± 2. 5 69. 3 ± 4. 1± 3. 6 77. 5 +7. 6 -7. 8 62. 9 +6. 0 -5. 9 69. 3 ± 5. 5 Number runs 45 49 94 157 SAGE 79. 4 +8. 8 -8. 4 ± 3. 9 65. 0 +5. 1 -4. 9± 3. 4 68. 9 +4. 5 -4. 3 ± 3. 4 66. 3 +3. 3 -3. 2 +3. 5 -3. 2 79. 4 +9. 6 -9. 3 65. 0 +6. 1 -6. 0 68. 9 +5. 6 -5. 5 66. 3 +4. 8 -4. 5 Number runs (110) (107) (217) (288) SAGE+GALLEX/GNO 78. 3 ± 5. 9 63. 9 ± 4. 2 69. 1 ± 3. 9 67. 6 ± 3. 6 Δ ~ 2σ –
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 variation without χ2/dof 10. 8/5 13. 2/6 prob 5. 6% 4. 0% χ2/dof 11. 7/16 11. 4/17 prob 76% 83% At the present time we cannot differentiate between these two hypotheses, but it should become possible to do so with additional data.
Future • Further running for the next three years. • Measurement of the response of a Ga solar neutrino experiment to neutrinos from a 51 Cr source with accuracy better than 5%.
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