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Register a new userComprehensive geoneutrino analysis with Borexino
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This paper presents a geoneutrino measurement using 3262.74 days of data taken with the Borexino detector at LNGS in Italy. By observing $52.6 ^{+9.4}_{-8.6} ({rm stat}) ^{+2.7}_{-2.1}({rm sys})$ geoneutrinos (68% interval) from $^{238}$U and $^{232}$Th, a signal of $47.0^{+8.4}_{-7.7},({rm stat)}^{+2.4}_{-1.9},({rm sys})$ TNU with $^{+18.3}_{-17.2}$% total precision was obtained. This result assumes the same Th/U mass ratio found in chondritic CI meteorites but compatible results were found when contributions from $^{238}$U and $^{232}$Th were fit as free parameters. Antineutrino background from reactors is fit unconstrained and found compatible with the expectations. The null-hypothesis of observing a signal from the mantle is excluded at a 99.0% C.L. when exploiting the knowledge of the local crust. Measured mantle signal of $21.2 ^{+9.6}_{-9.0} ({rm stat})^{+1.1}_{-0.9} ({rm sys})$ TNU corresponds to the production of a radiogenic heat of $24.6 ^{+11.1}_{-10.4}$ TW (68% interval) from $^{238}$U and $^{232}$Th in the mantle. Assuming 18% contribution of $^{40}$K in the mantle and $8.1^{+1.9}_{-1.4}$ TW of radiogenic heat of the lithosphere, the Borexino estimate of the total Earth radiogenic heat is $38.2 ^{+13.6}_{-12.7}$ TW, corresponding to a convective Urey ratio of 0.78$^{+0.41}_{-0.28}$. These values are compatible with different geological models, however there is a 2.4$sigma$ tension with those which predict the lowest concentration of heat-producing elements. By fitting the data with a constraint on the reactor antineutrino background, the existence of a hypothetical georeactor at the center of the Earth having power greater than 2.4 TW at 95% C.L. is excluded. Particular attention is given to all analysis details, which should be of interest for the next generation geoneutrino measurements.
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We propose to include in the analysis of Borexino single event energy spectrum the scattering of $^{40}$K geo-antineutrinos by scintillator electrons. The Hydridic Earth model predicts the concentration of potassium in modern Earth from 1% to 4% of the Earth mass. We calculated contribution of $^{40}$K geo-antineutrino interactions in single Borexino events for these concentrations. This contribution is comparable to the contribution from the interaction of CNO neutrinos. We discuss the reasons for using the Hydridic Earth model.
Borexino is a massive calorimetric liquid scintillation detector whose installation has been completed in the underground Gran Sasso Laboratory. The focus of the experiment is on the direct and real time measurement of the flux of neutrinos produced in the $^{7}Be$ electron capture reaction in the Sun. Furthermore, recent studies about the reduction of the $^{11}C$ background through suitable rejection techniques demonstrated the possibility to open an interesting additional observation window in the energy region of the pep and CNO solar neutrinos. Beyond the solar neutrino program, the detector will be also a powerful observatory for antineutrinos from Supernovae, as well as for geoneutrinos, profiting from a very low background from nuclear reactors.
Borexino is a large-volume liquid scintillator detector installed in the underground halls of the Laboratori Nazionali del Gran Sasso in Italy. After several years of construction, data taking started in May 2007. The Borexino phase I ended after about three years of data taking. Borexino provided the first real time measurement of the $^{7}$Be solar neutrino interaction rate with accuracy better than 5% and confirmed the absence of its day-night asymmetry with 1.4% precision. This latter Borexino results alone rejects the LOW region of solar neutrino oscillation parameters at more than 8.5 $sigma$ C.L. Combined with the other solar neutrino data, Borexino measurements isolate the MSW-LMA solution of neutrino oscillations without assuming CPT invariance in the neutrino sector. Borexino has also directly observed solar neutrinos in the 1.0-1.5 MeV energy range, leading to the first direct evidence of the $pep$ solar neutrino signal and the strongest constraint of the CNO solar neutrino flux up to date. Borexino provided the measurement of the solar $^{8}$B neutrino rate with 3 MeV energy threshold.
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 $mu_{ u}^{eff}$ $<$ 2.8$cdot$10$^{-11}$ $mu_{B}$ 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.
Neutrinos are elementary particles which are known since many years as fundamental messengers from the interior of the Sun. The Standard Solar Model, which gives a theoretical description of all nuclear processes which happen in our star, predicts that roughly 99% of the energy produced is coming from a series of processes known as the pp chain. Such processes have been studied in detail over the last years by means of neutrinos, thanks also to the important measurements provided by the Borexino experiment. The remaining 1% is instead predicted to come from a separate loop-process, known as the CNO cycle. This sub-dominant process is theoretically well understood, but has so far escaped any direct observation. Another fundamental aspect is that the CNO cycle is indeed the main nuclear engine in stars more massive than the Sun. In 2020, thanks to the unprecedented radio-purity and temperature control achieved by the Borexino detector over recent years, the first ever detection of neutrinos from the CNO cycle has been finally announced. The milestone result confirms the existence of this nuclear fusion process in our Universe. Here, the details of the detector stabilization and the analysis techniques adopted are reported.
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