The Borexino Thermal Monitoring & Management System and simulations of the fluid-dynamics of the Borexino detector under asymmetrical, changing boundary conditions

A comprehensive monitoring system for the thermal environment inside the Borexino neutrino detector was developed and installed in order to reduce uncertainties in determining temperatures throughout the detector. A complementary thermal management system limits undesirable thermal couplings between the environment and Borexino's active sections. This strategy is bringing improved radioactive background conditions to the region of interest for the physics signal thanks to reduced fluid mixing induced in the liquid scintillator. Although fluid-dynamical equilibrium has not yet been fully reached, and thermal fine-tuning is possible, the system has proven extremely effective at stabilizing the detector's thermal conditions while offering precise insights into its mechanisms of internal thermal transport. Furthermore, a Computational Fluid-Dynamics analysis has been performed, based on the empirical measurements provided by the thermal monitoring system, and providing information into present and future thermal trends. A two-dimensional modeling approach was implemented in order to achieve a proper understanding of the thermal and fluid-dynamics in Borexino. It was optimized for different regions and periods of interest, focusing on the most critical effects that were identified as influencing background concentrations. Literature experimental case studies were reproduced to benchmark the method and settings, and a Borexino-specific benchmark was implemented in order to validate the modeling approach for thermal transport. Finally, fully-convective models were applied to understand general and specific fluid motions impacting the detector's Active Volume.Comment: arXiv admin note: substantial text overlap with arXiv:1705.09078, arXiv:1705.0965

Spectroscopy of geo-neutrinos from 2056 days of Borexino data

We report an improved geo-neutrino measurement with Borexino from 2056 days of data taking. The present exposure is $(5.5\pm0.3)\times10^{31}$ proton$\times$yr. Assuming a chondritic Th/U mass ratio of 3.9, we obtain $23.7 ^{+6.5}_{-5.7} (stat) ^{+0.9}_{-0.6} (sys)$ geo-neutrino events. The null observation of geo-neutrinos with Borexino alone has a probability of $3.6 \times 10^{-9}$ (5.9$\sigma$). A geo-neutrino signal from the mantle is obtained at 98\% C.L. The radiogenic heat production for U and Th from the present best-fit result is restricted to the range 23-36 TW, taking into account the uncertainty on the distribution of heat producing elements inside the Earth.Comment: 4 pages, 4 figure

The Main Results of the Borexino Experiment

The main physical results on the registration of solar neutrinos and the search for rare processes obtained by the Borexino collaboration to date are presented.Comment: 8 pages, 8 figgures, To be published as Proceedings of the Third Annual Large Hadron Collider Physics Conference, St. Petersburg, Russia, 201

Measurement of neutrino flux from the primary proton--proton fusion process in the Sun with Borexino detector

Neutrino produced in a chain of nuclear reactions in the Sun starting from the fusion of two protons, for the first time has been detected in a real-time detector in spectrometric mode. The unique properties of the Borexino detector provided an oppurtunity to disentangle pp-neutrino spectrum from the background components. A comparison of the total neutrino flux from the Sun with Solar luminosity in photons provides a test of the stability of the Sun on the 10$^{5}$ years time scale, and sets a strong limit on the power production in the unknown energy sources in the Sun of no more than 4\% of the total energy production at 90\% C.L.Comment: 15 pages, 2 tables, 3 figure

Light Sterile Neutrinos: A White Paper

This white paper addresses the hypothesis of light sterile neutrinos based on recent anomalies observed in neutrino experiments and the latest astrophysical data

Development of dynamic models for neutron transport calculations

A quasi-static approach within the framework of neutron transport theory is used to develop a computational tool for the time-dependent analysis of nuclear systems. The determination of the shape function needed for the quasistatic scheme is obtained by the steady-state transport code DRAGON. The kinetic model solves the system of ordinary differential equations for the amplitude function on a fast scale. The kinetic parameters are calculated by a coupling module that retrieves the shape from the output of the transport code and performs the required adjoint-weighted quadratures. When the update of the shape has to be carried out, the coupling module generates an appropriate input file for the transport code. Both the standard Improved Quasi-Static scheme and an innovative Predictor-Corrector algorithm are implemented. The results show the feasibility of both procedures and their effectiveness in terms of computational times and accuracy

Modulations of the cosmic muon signal in ten years of Borexino data

We have measured the flux of cosmic muons in the Laboratori Nazionali del Gran Sasso at 3800 m w.e. to be (3.432 ± 0.003)⋅ 10−4 m−2s−1 based on ten years of Borexino data acquired between May 2007 and May 2017. A seasonal modulation with a period of (366.3 ± 0.6) d and a relative amplitude of (1.36 ±0.04)% is observed. The phase is measured to be (181.7 ± 0.4) d, corresponding to a maximum at the 1st of July. Using data inferred from global atmospheric models, we show the muon flux to be positively correlated with the atmospheric temperature and measure the effective temperature coefficient αT = 0.90 ± 0.02. The origin of cosmic muons from pion and kaon decays in the atmosphere allows to interpret the effective temperature coefficient as an indirect measurement of the atmospheric kaon-to-pion production ratio rK/π = 0.11+0.11−0.07 for primary energies above 18 TeV. We find evidence for a long-term modulation of the muon flux with a period of ~ 3000 d and a maximum in June 2012 that is not present in the atmospheric temperature data. A possible correlation between this modulation and the solar activity is investigated. The cosmogenic neutron production rate is found to show a seasonal modulation in phase with the cosmic muon flux but with an increased amplitude of (2.6 ± 0.4)%