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Soviet–American Gallium Experiment

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SAGE (Soviet–American Gallium Experiment, or sometimes Russian-American Gallium Experiment) is a collaborative experiment devised by several prominent physicists to measure the solar neutrino flux.

The experiment

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SAGE was devised to measure the radio-chemical solar neutrino flux based on the inverse beta decay reaction, 71Ga 71Ge. The target for the reaction was 50-57 tonnes of liquid gallium metal stored deep (2100 meters) underground at the Baksan Neutrino Observatory in the Caucasus Mountains in Russia. The laboratory containing the SAGE-experiment is called gallium-germanium neutrino telescope (GGNT) laboratory, GGNT being the name of the SAGE experimental apparatus. About once a month, the neutrino induced Ge is extracted from the Ga. 71Ge is unstable with respect to electron capture (  days) and, therefore, the amount of extracted germanium can be determined from its activity as measured in small proportional counters.

The experiment had begun to measure the solar neutrino capture rate with a target of gallium metal in December 1989 and continued to run in August 2011 with only a few brief interruptions in the timespan. As of 2013 is the experiment was described as "being continued"[1] with the latest published data from August 2011. As of 2014 it was stated that the SAGE experiment continues the once-a-month extractions.[2] The SAGE experiment continued in 2016.[3] As of 2017, the SAGE-experiment continues.[4]

The experiment has measured the solar neutrino flux in 168 extractions between January 1990 and December 2007. The result of the experiment based on the whole 1990-2007 set of data is 65.4+3.1
−3.0 (stat.) +2.6
−2.8 (syst.) SNU. This represents only 56%-60% of the capture rate predicted by different Standard Solar Models, which predict 138 SNU. The difference is in agreement with neutrino oscillations.

The collaboration has used a 518 kCi 51Cr neutrino source to test the experimental operation. The energy of these neutrinos is similar to the solar 7Be neutrinos and thus makes an ideal check on the experimental procedure. The extractions for the Cr experiment took place between January and May 1995 and the counting of the samples lasted until fall. The result, expressed in terms of a ratio of the measured production rate to the expected production rate, is 1.0±0.15. This indicates that the discrepancy between the solar model predictions and the SAGE flux measurement cannot be an experimental artifact.

The gallium anomaly

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In 2003-2004, a 37Ar neutrino source was made by irradiation of calcium oxide in the BN-600 reactor followed by chemical separation of argon. A calibration experiment with it was performed from April 30th to September 27th. The resulting production of 71Ge was calculated in 2005 to be 79% of expected,[5] confirming an earlier (1998) estimate from one of the experiments on GALLEX (another gave results indistinguishable from 100%, similarly to the Cr experiment on SAGE).[6][7] This discrepancy soon became known as the gallium anomaly.

Following the report of the anomaly in 2006, physicists began to explore potential explanations for the observed deficit. A 2007 analysis[8] examined the data within frameworks of two- and three-neutrino mixing, considering the possibility of electron neutrinos oscillating into a hypothetical sterile neutrino. By 2009, a thorough investigation into potential experimental errors had verified the efficiency of chemical extraction of germanium, counting procedures and data analysis techniques, ruling out significant experimental errors.[9][10] This strengthened the evidence for the anomaly and pushed the focus towards investigating potential new physics beyond the standard three-neutrino model. A 2013 review combined the gallium results with data from reactor antineutrino experiments, arguing for a consistent pattern of electron (anti)neutrino disappearance at short baselines and highlighting the need for more precise measurements and dedicated experiments to definitively confirm or refute the sterile neutrino interpretation.[11]

Baksan Experiment on Sterile Transitions (BEST)

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In 2014, the SAGE-experiment's GGNT-apparatus (gallium-germanium neutrino telescope) was upgraded to perform a very-short-baseline neutrino oscillation experiment BEST (Baksan Experiment on Sterile Transitions) with an intense artificial neutrino source based on 51Cr.[12] In 2017, the BEST apparatus was completed, but the artificial neutrino source was missing.[13] As of 2018, the BEST experiment was underway.[14] As of 2018, a follow-up experiment BEST-2 where the source would be changed to 65Zn was under consideration.[15] It uses two gallium chambers instead of one, to better determine whether the anomaly could be explained by the distance from the source of the neutrinos.[16]

In June 2022, the BEST experiment released two papers observing a 20-24% deficit in the production the isotope germanium expected from the reaction  , confirming previous results from SAGE and GALLEX on the so called "gallium anomaly" pointing out that a sterile neutrino explanation can be consistent with the data.[17][18][19] Further work have refined the precision for the cross section of the neutrino capture in 2023[20] which was proposed as a possible inaccuracy source back in 1998[21] as well as half-life of   in 2024[22] ruling them out as possible explanations for the anomaly.[16]

Members of SAGE

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SAGE is led by the following physicists:

See also

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  • GALLEX/GNO was the second (of two) large gallium-germanium radiochemical experiment. It was running in 1991-2003.
  • Hans Bethe was the architect of the theory of nuclear fusion reactions in stars.
  • The University of Washington is playing a major role in the statistical analysis of the SAGE data and in the determination of systematic uncertainties. They are very active in the remaining analysis of the Cr experiment data as well as the solar neutrino data.

References

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  1. ^ Gavrin, V. N. (October 2013). "Contribution of gallium experiments to the understanding of solar physics and neutrino physics". Physics of Atomic Nuclei. 76 (10): 1238–1243. Bibcode:2013PAN....76.1238G. doi:10.1134/S106377881309007X. S2CID 122656176.
  2. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2020-10-25. Retrieved 2018-12-15.{{cite web}}: CS1 maint: archived copy as title (link)
  3. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2019-05-31. Retrieved 2019-05-31.{{cite web}}: CS1 maint: archived copy as title (link)
  4. ^ "Baksan scales new neutrino heights – CERN Courier". 19 May 2017.
  5. ^ Abdurashitov, J. N.; Gavrin, V. N.; Girin, S. V.; Gorbachev, V. V.; Gurkina, P. P.; Ibragimova, T. V.; Kalikhov, A. V.; Khairnasov, N. G.; Knodel, T. V.; Matveev, V. A.; Mirmov, I. N.; Shikhin, A. A.; Veretenkin, E. P.; Vermul, V. M.; Yants, V. E. (2006-04-20). "Measurement of the response of a Ga solar neutrino experiment to neutrinos from an 37Ar source". Physical Review C. 73 (4): 045805. arXiv:nucl-ex/0512041. doi:10.1103/PhysRevC.73.045805. ISSN 0556-2813.
  6. ^ Hampel, W; Heusser, G; Kiko, J; Kirsten, T; Laubenstein, M; Pernicka, E; Rau, W; Rönn, U; Schlosser, C; Wójcik, M; v. Ammon, R; Ebert, K. H; Fritsch, T; Heidt, D; Henrich, E (1998-02-19). "Final results of the 51Cr neutrino source experiments in GALLEX". Physics Letters B. 420 (1): 114–126. doi:10.1016/S0370-2693(97)01562-1. ISSN 0370-2693.
  7. ^ Giunti, C. (2013-04-01). "Status of Sterile Neutrinos". Nuclear Physics B - Proceedings Supplements. Proceedings of the Neutrino Oscillation Workshop. 237–238: 295–300. doi:10.1016/j.nuclphysbps.2013.04.111. ISSN 0920-5632.
  8. ^ Acero, Mario A.; Giunti, Carlo; Laveder, Marco (2008-10-16). "Limits on nu_e and anti-nu_e disappearance from Gallium and reactor experiments". Physical Review D. 78 (7): 073009. arXiv:0711.4222. doi:10.1103/PhysRevD.78.073009. ISSN 1550-7998.
  9. ^ SAGE Collaboration; Abdurashitov, J. N.; Gavrin, V. N.; Gorbachev, V. V.; Gurkina, P. P.; Ibragimova, T. V.; Kalikhov, A. V.; Khairnasov, N. G.; Knodel, T. V.; Mirmov, I. N.; Shikhin, A. A.; Veretenkin, E. P.; Yants, V. E.; Zatsepin, G. T.; Bowles, T. J. (2009-07-30). "Measurement of the solar neutrino capture rate with gallium metal. III: Results for the 2002--2007 data-taking period". Physical Review C. 80 (1): 015807. arXiv:0901.2200. doi:10.1103/PhysRevC.80.015807. ISSN 0556-2813.
  10. ^ Gavrin, Vladimir N (2011-09-30). "The Russian-American gallium experiment SAGE". Physics-Uspekhi. 54 (9): 941–949. doi:10.3367/UFNe.0181.201109g.0975. ISSN 1063-7869.
  11. ^ Giunti, C. (2013-04-01). "Status of Sterile Neutrinos". Nuclear Physics B - Proceedings Supplements. Proceedings of the Neutrino Oscillation Workshop. 237–238: 295–300. doi:10.1016/j.nuclphysbps.2013.04.111. ISSN 0920-5632.
  12. ^ Gavrin, V.; Cleveland, B.; Danshin, S.; Elliott, S.; Gorbachev, V.; Ibragimova, T.; Kalikhov, A.; Knodel, T.; Kozlova, Yu.; Malyshkin, Yu.; Matveev, V.; Mirmov, I.; Nico, J.; Robertson, R. G. H.; Shikhin, A.; Sinclair, D.; Veretenkin, E.; Wilkerson, J. (2015). "Current status of new SAGE project with 51Cr neutrino source". Physics of Particles and Nuclei. 46 (2): 131. Bibcode:2015PPN....46..131G. doi:10.1134/S1063779615020100. OSTI 1440431. S2CID 120787161.
  13. ^ "Baksan scales new neutrino heights – CERN Courier". 19 May 2017.
  14. ^ Babenko, Maxim; Overbye, Dennis (2018-07-16). "The Neutrino Trappers". The New York Times.
  15. ^ Gavrin, V. N.; Gorbachev, V. V.; Ibragimova, T. V.; Kornoukhov, V. N.; Dzhanelidze, A. A.; Zlokazov, S. B.; Kotelnikov, N. A.; Izhutov, A. L.; Mainskov, S. V.; Pimenov, V. V.; Borisenko, V. P.; Kiselev, K. B.; Tsevelev, M. P. (2018). "On the gallium experiment BEST-2 with a 65Zn source to search for neutrino oscillations on a short baseline". arXiv:1807.02977 [physics.ins-det].
  16. ^ a b O'Callaghan, Jonathan (2024-07-12). "What Could Explain the Gallium Anomaly?". Quanta Magazine. Retrieved 2024-07-14.
  17. ^ Laboratory, Los Alamos National (2022-06-18). "Deep Underground Experiment Results Confirm Anomaly: Possible New Fundamental Physics". SciTechDaily. Retrieved 2022-06-22.
  18. ^ Barinov, V. V.; Cleveland, B. T.; Danshin, S. N.; Ejiri, H.; Elliott, S. R.; Frekers, D.; Gavrin, V. N.; Gorbachev, V. V.; Gorbunov, D. S.; Haxton, W. C.; Ibragimova, T. V. (2022-06-09). "Results from the Baksan Experiment on Sterile Transitions (BEST)". Physical Review Letters. 128 (23): 232501. arXiv:2109.11482. Bibcode:2022PhRvL.128w2501B. doi:10.1103/PhysRevLett.128.232501. PMID 35749172. S2CID 237605431.
  19. ^ Barinov, V. V.; Danshin, S. N.; Gavrin, V. N.; Gorbachev, V. V.; Gorbunov, D. S.; Ibragimova, T. V.; Kozlova, Yu. P.; Kravchuk, L. V.; Kuzminov, V. V.; Lubsandorzhiev, B. K.; Malyshkin, Yu. M. (2022-06-09). "Search for electron-neutrino transitions to sterile states in the BEST experiment". Physical Review C. 105 (6): 065502. arXiv:2201.07364. Bibcode:2022PhRvC.105f5502B. doi:10.1103/PhysRevC.105.065502. S2CID 246035834.
  20. ^ Elliott, S. R.; Gavrin, V. N.; Haxton, W. C.; Ibragimova, T. V.; Rule, E. J. (2023-09-25). "Gallium neutrino absorption cross section and its uncertainty". Physical Review C. 108 (3): 035502. arXiv:2303.13623. doi:10.1103/PhysRevC.108.035502. ISSN 2469-9985.
  21. ^ Haxton, W. C. (July 1998). "Cross Section Uncertainties in the Gallium Neutrino Source Experiments". Physics Letters B. 431 (1–2): 110–118. arXiv:nucl-th/9804011. doi:10.1016/S0370-2693(98)00581-4.
  22. ^ Norman, E. B.; Drobizhev, A.; Gharibyan, N.; Gregorich, K. E.; Kolomensky, Yu. G.; Sammis, B. N.; Scielzo, N. D.; Shusterman, J. A.; Thomas, K. J. (2024-05-30). "Half-life of Ge 71 and the gallium anomaly". Physical Review C. 109 (5): 055501. doi:10.1103/PhysRevC.109.055501. ISSN 2469-9985.

Literature

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43°16′32″N 42°41′25″E / 43.27556°N 42.69028°E / 43.27556; 42.69028

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