Neutrino-Oscillation Searches in the Short-Baseline Gallium Experiment BEST-2 with a 65 Zn Source
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EMENTARY PARTICLES AND FIELDS Experiment
Neutrino-Oscillation Searches in the Short-Baseline Gallium Experiment BEST-2 with a 65 Zn Source V. N. Gavrin1), V. V. Gorbachev1)* , T. V. Ibragimova1), V. N. Kornoukhov1), A. A. Dzhanelidze2) , S. B. Zlokazov2) , N. A. Kotelnikov2), A. L. Izhutov3) , S. V. Mainskov3), V. V. Pimenov3) , V. P. Borisenko4), K. B. Kiselev4) , and M. P. Tsevelev4) Received June 13, 2018; revised June 13, 2018; accepted June 13, 2018
Abstract—The possibility of employing a 65 Zn source in the gallium experiment BEST-2 with the aim of constraining the region of allowed oscillation parameters is examined. The source activity required for the BEST-2 experiment is calculated, and the size of the source and its effect on the results of oscillation measurements are discussed along with the possibilities for producing such a source. Various schemes for implementing respective measurements are considered. DOI: 10.1134/S106377881901006X
interactions is determined from the number of 71 Ge atoms produced. In the BEST experiment, searches for oscillations over a short baseline will be performed on the basis of an analysis of the rates of capture of electron neutrinos originating from an intense 51 Cr source of activity 3 MCi on nuclei of the gallium target [1]. The target, which contains 50 t of liquid metallic gallium, is separated into two zones—an inner spherical and an outer cylindrical one—having a common center. The source of volume about 1 l is placed at the center of the two zones in a tube going from the top along the axis of the cylindrical target zone. If the neutrinos from the source have identical mean free paths in the two target zones—that is, if, in 4π geometry, gallium in the target has identical thicknesses—the rates of neutrino capture in the two zones are identical, taking a value of 65 d−1 , the rate of solar-neutrino capture over the whole target being about 1 d−1 . Oscillations change the neutrino flavor and reduce the rate of electron-neutrino capture. In the case of oscillations over a short baseline, the probability for electron-neutrino-flavor conservation is given by 2 2 2 1.27 × Δm L , (1) Pee = 1 − sin 2θ sin E
1. INTRODUCTION Several experiments with various neutrino sources are being prepared at the present time with the aim of testing the sterile-neutrino hypothesis or, in other words, the existence of a fourth neutrino mass eigenstate [1–4]. In the present article, we demonstrate the potential of the BEST-2 experiment that employs an intense artificial neutrino source on the basis of 65 Zn and a two-zone gallium target [5, 6]. The BEST-2 experiment is treated as a continuation of and a supplement to the BEST experiment with a 51 Cr source of activity 3 MCi [1, 2]. 2. THE BEST EXPERIMENT The BEST experiment is being prepared on the basis of the gallium–germanium neutrino telescope (GGNT) at the Baksan Neutrino Observatory (BNO), Institute for Nuclear Research (INR), Russian Academy of Sciences (RAS). Since 1990, this telescope has been employed for solar-neutrino measurem
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