BNO INR RAS June 22 to July 2

BNO INR RAS June 22 to July 2, 2020 SAGE and BEST V. N. Gavrin on behalf of the BEST collaboration Baksan Neutrino Observatory of the Institute for Nuclear Research of the Russian Academy of Sciences

North Caucasus Kabardino-Balkar ian Republic Baksan valley BNO INR RAS location mt. Andyrchi Village Neutrino

BNO INR RAS 22 to July 2, 2020 Outline • Introduction and a little bit of history. • SAGE. Present Ga results. • Source experiments. • The BEST. Intermediate Results • Summary

BNO INR RAS June 22 to July 2, 2020 Ga experiments SAGE 50 tons of metallic Ga 168 runs (Jan 1990 – Dec 2007) result 65. 4+4. 0 -4. 1 SNU [Phys. Rev. C 80, 015807 (2009)] 71 Ga(v e, e-)71 Ge, Eth = 233 ke. V The Russian-American experiment SAGE began to measure the solar neutrino capture rate with a target of gallium metal in December 1989 GALLEX (May 1991 – Jan 1997) GNO (May 1998 – Apr 2003 30 t of Ga (103 tons of Ga. Cl 3 acidic solution) GALLEX, 65 runs: 73. 1+7. 1 -7. 3 SNU (at TAUP 2007) GNO, 58 runs: 62. 9+5. 5 -5. 3 SNU GALLEX + GNO : 67. 5 ± 5. 1 SNU The first Ga experiments results provided a direct indication of the neutrino oscillations existence that became a strong justification for the SNO experiment. (1 SNU = 1 interaction/s in a target that contains 1036 atoms of the neutrino absorbing isotope). ). The weighted average of the results of all Ga solar experiments is 66. 1± 3. 1 SNU. Ga experiments have shown deficit of solar neutrino in the entire energy range.

BNO INR RAS June 22 to July 2, 2020 SAGE & GALLEX neutrino source experiments Neutrino sources: 51 Cr: 37 Ar: 747 ke. V (81. 6%), 427 ke. V (9. 0%), 752 ke. V (8. 5%), 432 ke. V (0. 9%) 811 ke. V (90. 2%), 813 ke. V (9. 8%) 1994 – 1995 A(Cr 1) = 1. 714 ± 0. 036 MCi 1995 – 1996 A(Cr 2) = 1. 868 ± 0. 073 MCi GALLEX: Results: PLB 342 (1995) GALLEX: R 1(Cr) = 0. 953 ± 0. 11 1994 – 1995 A(Cr) = 0. 517 ± 0. 006 MCi 2004 A(Ar) = 0. 409 ± 0. 002 MCi SAGE: PRC 59 (1999) SAGE: R 3(Cr) = 0. 95 ± 0. 12 PLB 420 (1998) R 2(Cr) = 0. 812 ± 0. 10 PRC 73 (2006) R 4(Ar) = 0. 791 ± 0. 084 R – ratio of the measured production rate to that expected [Bahcall 97] (no uncertainty on cross section included) The differences of 4 times in activities and more then 2 times in target masses result in equal uncertainties of the experiments. The cause is different sensitivity of the targets to ν from sources and dimensions of the sources. Gallium anomaly: [Mario A. Acero, Carlo Giunti, and Marco Laveder. Phys. Rev. D 78, 073009 (2008), ar. Xiv: 0711. 4222 v 3] The neutrino capture rate measured by the Ga detectors SAGE with 51 Cr and 37 Ar artificial neutrino sources is considerably less than expected. Rave-Bahcall = 0. 87 ± 0. 05 (2. 6σ) Rave-Frefers = 0. 84 ± 0. 05 (2. 9σ) [S Gariazzo, C Giunti, M Laveder, Y F Li, E M Zavanin, ar. Xiv: 1507. 08204 v 1 [hep-ph]]

BNO INR RAS June 22 to July 2, 2020 Region of allowed mixing parameters inferred from 4 gallium source experiments assuming oscillations to a sterile neutrino In Ga experiments: Oscillations affect the capture rate with Eν~ 1 Me. V L~1 m Δm 2 ~ 1 e. V 2 Limits for oscillation parameters obtained in the four artificial neutrino source experiments: the best-fit point (●) at Δm 2 = 2. 15 e. V 2 and sin 2(2θ)=0. 24 χ2/dof=1. 77/2, GOF=41% [ar. Xiv: 1006. 2103 [nucl-ex]]

BNO INR RAS June 22 to July 2, 2020 First proposal of two zone Ga experiment with 51 Cr (3 MCi) source ar. Xiv: 1006. 2103 v 2 [nucl-ex] The region in Δm 2 - sin 2(2θ) space to which the new 3 MCi 51 Cr experiment will be sensitive The rate at SOE: 64. 5 atoms/day Target: 50 т Ga metall Masses of the zones: 8 t and 42 t Path length in each zone: <L> = 55 cm σ – cross sect. {5. 8× 10 -45 cm 2 [Bahcall]} Since 2011 construction of the BEST experiment installation started [Physics of Particles and Nuclei. 2015. Vol. 46, No. 2. pp. 131 -137] ar. Xiv: 1204. 5379 v 1 [hep-ph] 18 Apr 2012

BNO INR RAS 22 to July 2, 2020 BEST installation scheme Ga 71 Ge extraction (30 hours in total) : 1) Pumping gallium from zones to chemical reactors: internal zone → 1 reactor, external zone → 6 reactors; ( 4. 5 h). 2) In each reactor the germanium carrier in the form of Ge. Cl 4 is extracted from the metal into aqueous phase. 3) Concentration of the aqueous solution by evaporation. (16 h) 4) Synthesis of Ge. H 4 and placing it into a proportional counter. 5) 71 Ge decays are counted. ( 60 – 150 days) νe + 71 Ga → 71 Ge + e. Source activity measurement: 1) Moving the source into a lead container 2) Measuring gamma spectrum at 21. 65 m distance with a semiconductor detector ( 1 h) 3) Moving the source into a calorimeter 4) Measuring the heat emitted by the source ( 20 -21 h )

BNO INR RAS 22 to July 2, 2020 etr m i r o l Ca Lead chamber 2 zone gallium target Source

BNO INR RAS 22 to July 2, 2020 BEST installation

BNO INR RAS June 22 to July 2, 2020 BEST: Neutrino source Biological protection , tangsten Stainless steel 4 kg 97%-enriched 50 Cr, 26 chrome metal disks h = 4 mm, 84 and 88 mm. 26 chrome metal disks Stainless steel Chromium disks from metallic 50 Cr enriched up to 97% (the enrichment was performed by the JSC “PA “Electrochemical Plant” (Zelenogorsk) ) were irradiated for ~ 100 days with thermal neutrons in the SM-3 reactor (RIAR, Dmitrovgrad). Thermal neutron flux density – 5× 1015 neutrons /(cm 2 sec)

BNO INR RAS 22 to July 2, 2020 The source was immediately placed at the center of the two-zone target of liquid gallium. First stage of the BEST experiment began. In the photos you see the moment of source overload from a transport container into a two-zone Ga target. At 14: 02 Moscow time the first irradiation of the two-zone gallium target has started.

BNO INR RAS 22 to July 2, 2020 The BEST stages 1. Working with the 51 Cr source (completed on October 2019): - 10 exposures of a 2 -zone gallium target by the source - 20 extractions from 2 zones of gallium target, - 10 calorimetric measurements of the source activity, - 11 spectrometric measurements of the gamma spectrum of the source, - synthesis of germane (Ge. H 4) and filling counters - installation of filled counters in the counting systems 2. 71 Ge decay measurements (completed on March 2020): - primary data collection and processing, - preliminary data analysis - comparative crosscheck data analysis 3. Tests and checks (around the end of August ): - production of 37 Ar, 71 Ge isotopes - verification of counting systems, - measurement of the counters volumetric and peak efficiencies, - estimation of all systematic uncertainties 4. Interpretation and presentation of results (September 2020)

BNO INR RAS June 22 to July 2, 2020 Extraction schedule and related parameters The times of exposure are given in days of year 2019 10 targets irradiations: Mean exposure time - 9. 18 d; Masses : 7. 4 t and 40. 09 t; Mean extraction eff. from Ga is 98%; Mean the overall efficiency including synthesis into the counting gas Ge. H 4 - 96%; The efficiency of extraction was measured by adding to the Ga a known mass of inactive Ge carrier before the start of exposure to the neutrino source and measuring the mass of extracted Ge. The mass of added carriers of ~2. 4 µmol of 72 Ge (92%) and 76 Ge(95%) were used.

BNO INR RAS June 22 to July 2, 2020 Full spectrum of photons from the source Gamma-ray spectroscopy Measured nuclide impurities in the 51 Cr source and their contribution to the source activity measurement at the reference time 14: 02 on 05. 07. 2019 Part spectrum of photons from the source (600 -900 ke. V) (V. V. Gorbachev, Poster session at XXXV International Conference on Equations on State for Matter, Elbrus, KBR, March 1 -6, 2020) From 11 spectrometric measurements of gamma radiation of the source was obtained: - the total amount of heat release from impurity radionuclides is 2. 9 ± 0. 5 m. W , which is ~ 4· 10 -6 of the initial 51 Cr source power, and can be neglected; - confirmation of a high purity of the material used to produce the 51 Cr source

BNO INR RAS 22 to July 2, 2020 Source power measurements with the calorimeter system. The source activity was measured by its heat release in the calorimetric system. 10 measurements of the 51 Cr neutrino source activity were done. The obtained value of the neutrino source activity on 05. 07. 2019 at 14: 02 is 3. 4099 ± 0. 008 МCi (total uncertainty includes the uncertainties of heat release (0. 015%) and energy release (0. 23%) added in quadrature). (Using a conversion factor of 217. 857 W/MCi 51 Cr the heat power of the 51 Cr source was 742. 87 W on July 5, 2019) For the first time, an artificial neutrino source of such high intensity was produced and for the first time so high accuracy in measuring such high activity was achieved. According to the passport from RIAR an estimated source activity was 3. 55 MCi on July 2, 2019 at 09: 40 (which corresponds 3. 28 MCi at the delivered time to BNO on July 5, 2019) [Yu. P. Kozlova. Measurement of Neutrino Source Activity in the experiment BEST by calorimetric method. Session of the Department of Nuclear Physics, Novosibirsk, March 10 -12, 2020]

BNO INR RAS 22 to July 2, 2020 BEST Collaboration: V. Gavrin*, V. Barinov, S. Danshin, V. Gorbachev, D. Gorbunov, T. Ibragimova, Yu. Kozlova, L. Kravchuk, V. Kuzminov, B. Lubsandorzhiev, Yu. Malyshkin, I. Mirmov, A. Shikhin, E. Veretenkin Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia B. Cleveland SNOLAB, Sudbury, ON P 3 Y 1 N 2, Canada H. Ejiri Research Center for Nuclear Physics, Osaka University, Osaka, Japan S. Elliott , I. Kim, R. Massarczyk Los Alamos National Laboratory, Los Alamos NM 87545, USA D. Frekers Institut für Kernphysik, Westfälische Wilhelms-Universität Munster, D-48149 Munster, Germany W. Haxton Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA V. Matveev, D. Naumov, G. Trubnikov, D. Filossov, S. Yakovenko Joint Institute for Nuclear Research (JINR) Joliot-Curie 6, 141980, Dubna, Moscow Region, Russia J. Nico National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD 20899, USA A. Petelin, V. Tarasov, A. Zvir JSC “State Scientific Center Research Institute of Atomic Reactors”, Dimitrovgrad, 433510, Russia R. Robertson Center for Experimental Nuclear Physics and Astrophysics, and Department of Physics, University of Washington, Seattle, WA 98195, USA D. Sinclair Carleton University 1125 Colonel By Drive Ottawa, K 1 S 5 B 6, Canada J. Wilkerson Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599, USA * Principal Investigator

BNO INR RAS 22 to July 2, 2020 Summary ● The BEST experiment - first direct search for neutrino oscillations into 4 -th flavor with radioactive source has started 5 July 2019 in BNO INR RAS ● The first stage of BEST is finished and the second stage is nearing completion. Currently preparatory works have begun for the implementation of the third final one. ● Spectrometric measurements of gamma radiation of the source shown a high purity of the material used to production the 51 Cr source and therefore a negligible contributions (~ 10 -6) from impurity radio nuclides to the calorimetric source activity measurements ● Obtained a precise value of the source activity from the calorimetric measurements which is 3. 4099 ± 0. 008 МCi on 05. 07. 2019 at 14: 02 ● Results of data measurements analysis is expected in September 2020

BNO INR RAS 22 to July 2, 2020 The authors express their sincere gratitude to Rosatom for the comprehensive support and fruitful cooperation in the implementation of the BEST experiment

BNO INR RAS 22 to July 2, 2020 Thank you for your attention