The 51Cr neutrino source and Borexino: a desirable marriage

Abstract

Exposure to a 51 Cr neutrino source as that used in Gallex will provide an excellent overall performance test of Borexino, which should collect about 1400 source induced events, with an initial rate of about 35 counts per day. This will be particularly important if MSW-small-angle turns out to be the solution of the solar neutrino problem. In addition, if an independent, accurate calibration is available, one will have an interesting experiment on neutrino properties: as an example, a neutrino magnetic moment of the order 5 · 10 −11 µ B could be detected/excluded at the 90% C.L.Borexino at Gran Sasso [1] has a lot to tell about 7 Be solar neutrinos: Standard Solar Models (SSMs) predict a rate λ ⊙ ≃ 50 counts per day (c.p.d.), mostly from the 7 Be neutrinos, over an estimated background λ b ≃ 10 c.p.d. At such rates, seasonal modulations of λ ⊙ , corresponding to variations in the earth-sun distance R ES , should allow a clean discrimination of signal to background. In addition, the Just-So oscillation mechanism predicts large seasonal modulations of the signal, well in excess of the 1/R 2 ES law, which are clearly detectable with Borexino.On the other hand, several scenarios predict much smaller event rates, comparable to or even smaller than the expected bacgkround: this is the case of the MSW-small-angle solutions, both for oscillations into active and sterile neutrinos. Also, if one insists on the massless neutrinos of the minimal electroweak theory, the available results (from Gallex

Probing neutrino nature at Borexino detector with chromium neutrino source

“…[1][2][3][4][5][6]. The first concept of the use of the artificial neutrino source comes from Alvarez, who proposed to use 65 Zn [7].…”

Neutrino electron scattering and electroweak gauge structure: Future tests

“…[19], the number of events would be drastically reduced and therefore the statistical error will be too large.…”

“…These have been suggested in order to test unusual neutrino electromagnetic properties, such as magnetic moments (see [6]). At present some experimentalists are considering the possibilities of these kind of physics [19,20]. Here we consider their role in testing the gauge structure of the electroweak interaction.…”

Neutrino scattering on polarized electron target as a test of neutrino magnetic moment

“…There are some experiments planned with different possible artificial sources, e.g. 51 Cr [7], 90 Sr [8,9], 147 Pm [10,11], 55 Fe [12]. The recently proposed measurement of neutrino magnetic moment at a level better than 10 −11 µ B ( ∼ 3 · 10 −12 µ B ) with the use of the tritium neutrino emitter (antineutrino source with the energy spectrum endpoint 18.6 keV) and a semiconductor cryodetector is planned to reach extra low threshold about 1.1 eV [13].…”