A search for the solar neutrino effective magnetic moment has been performed using data from 1291.5 days exposure during the second phase of the Borexino experiment. No significant deviations from the expected shape of the electron recoil spectrum from solar neutrinos have been found, and a new upper limit on the effective neutrino magnetic moment of μ eff ν < 2.8 × 10 −11 μ B at 90% C.L. has been set using constraints on the sum of the solar neutrino fluxes implied by the radiochemical gallium experiments. Using the limit for the effective neutrino moment, new limits for the magnetic moments of the neutrino flavor states, and for the elements of the neutrino magnetic moments matrix for Dirac and Majorana neutrinos, are derived.

We present the simultaneous measurement of the interaction rates R pp , R Be , R pep of pp, 7 Be, and pep solar neutrinos performed with a global fit to the Borexino data in an extended energy range (0.19-2.93) MeV with particular attention to details of the analysis methods. This result was obtained by analyzing 1291.51 days of Borexino Phase-II data, collected after an extensive scintillator purification campaign. Using counts per day ðcpdÞ=100 ton as unit, we find R pp ¼ 134 AE 10ðstatÞ þ6 −10 ðsysÞ, R Be ¼ 48.3 AE 1.1ðstatÞ þ0.4 −0.7 ðsysÞ; and R HZ pep ¼ 2.43 AE 0.36ðstatÞ þ0.15 −0.22 ðsysÞ assuming the interaction rate R CNO of CNO-cycle (Carbon, Nitrogen, Oxigen) solar neutrinos according to the prediction of the high metallicity standard solar model, and R LZ pep ¼ 2.65 AE 0.36ðstatÞ þ0.15 −0.24 ðsysÞ according to that of the low metallicity model. An upper limit R CNO < 8.1 cpd=100 ton (95% C.L.) is obtained by setting in the fit a constraint on the ratio R pp =R pep (47.7 AE 0.8 cpd=100 ton or 47.5 AE 0.8 cpd=100 ton according to the high or low metallicity hypothesis).

No abstract

This paper presents a comprehensive geoneutrino measurement using the Borexino detector, located at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The analysis is the result of 3262.74 days of data between December 2007 and April 2019. The paper describes improved analysis techniques and optimized data selection, which includes enlarged fiducial volume and sophisticated cosmogenic veto. The reported exposure of ð1.29 AE 0.05Þ × 10 32 protons × year represents an increase by a factor of two over a previous Borexino analysis reported in 2015. By observing 52.6 þ9.4 −8.6 ðstatÞ þ2.7 −2.1 ðsysÞ geoneutrinos (68% interval) from 238 U and 232 Th, a geoneutrino signal of 47.0 þ8.4 −7.7 ðstatÞ þ2.4 −1.9 ðsysÞ TNU with þ18.3 −17.2 % total precision was obtained. This result assumes the same Th/U mass ratio as found in chondritic CI meteorites but compatible results were found when contributions from 238 U and 232 Th were both fit as free parameters. Antineutrino background from reactors is fit unconstrained and found compatible with the expectations. The null-hypothesis of observing a geoneutrino signal from the mantle is excluded at a 99.0% C.L. when exploiting detailed knowledge of the local crust near the experimental site. Measured mantle signal of 21.2 þ9.5 −9.0 ðstatÞ þ1.1 −0.9 ðsysÞ TNU corresponds to the production of a radiogenic heat of 24.6 þ11.1 −10.4 TW (68% interval) from 238 U and 232 Th in the mantle. Assuming 18% contribution of 40 K in the mantle and 8.1 þ1.9 −1.4 TW of total radiogenic heat of the lithosphere, the Borexino estimate of the total radiogenic heat of the Earth is 38.2 þ13.6 −12.7 TW, which corresponds to the convective Urey ratio of 0.78 þ0.41 −0.28. These values are compatible with different geological predictions, however there is a ∼2.4σ tension with those Earth models which predict the lowest concentration of heat-producing elements in the mantle. In addition, by constraining the number of expected reactor antineutrino events, the existence of a hypothetical georeactor at the center of the Earth having power greater than 2.4 TW is excluded at 95% C.L. Particular attention is given to the description of all analysis details which should be of interest for the next generation of geoneutrino measurements using liquid scintillator detectors.

No abstract