Search

The Borexino detector has convincingly shown its outstanding performance in the in the sub-MeV regime through its unprecedented accomplishments in the solar and geo-neutrinos detection, which make it the ideal tool to unambiguously test the long-standing issue of the existence of a sterile neutrino, as suggested by several anomalies: the outputs of the LSND and Miniboone experiments, the results of the source calibration of the two Gallium solar νexperiments, and the recently hinted reactor anomaly. The SOX project will exploit two sources, based on chromium and cerium, which deployed under the experiment will emit two intense beams of νe(Cr) and νe‾(Ce). Interacting in the active volume of the liquid scintillator, each beam would create a spatial wave pattern in case of oscillation of the νe(or νe‾) into the sterile state, which would be the smoking gun proving the existence of the new sterile member of the neutrino family. Otherwise, its absence will allow setting very stringent limit on its existence.

The Borexino detector was built starting from 1996 in the underground hall C of Gran Sasso National Laboratory (LNGS) in Italy under about 1400 m of rock (3800 m.w.e) and it is mostly aimed to the study in real-time of the low-energy solar neutrinos.

The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. The primary reaction is the fusion of two protons into a deuteron, a positron and a neutrino. These neutrinos constitute the vast majority of neutrinos reaching Earth, providing us with key information about what goes on at the core of our star. Several experiments have now confirmed the observation of neutrino oscillations by detecting neutrinos from secondary nuclear processes in the Sun; this is the first direct spectral measurement of the neutrinos from the keystone proton-proton fusion. This observation is a crucial step towards the completion of the spectroscopy of pp-chain neutrinos, as well as further validation of the LMA-MSW model of neutrino oscillations.

Borexino has been running since May 2007 at the Laboratori Nazionali del Gran Sasso laboratory in Italy with the primary goal of detecting solar neutrinos. The detector, a large, unsegmented liquid scintillator calorimeter characterized by unprecedented low levels of intrinsic radioactivity, is optimized for the study of the lower energy part of the spectrum. During Phase-I (2007-2010), Borexino first detected and then precisely measured the flux of the 7Be solar neutrinos, ruled out any significant day-night asymmetry of their interaction rate, made the first direct observation of the pep neutrinos, and set the tightest upper limit on the flux of solar neutrinos produced in the CNO cycle (carbon, nitrogen, oxigen) where carbon, nitrogen, and oxygen serve as catalysts in the fusion process. In this paper we discuss the signal signature and provide a comprehensive description of the backgrounds, quantify their event rates, describe the methods for their identification, selection, or subtraction, and describe data analysis. Key features are an extensive in situ calibration program using radioactive sources, the detailed modeling of the detector response, the ability to define an innermost fiducial volume with extremely low background via software cuts, and the excellent pulse-shape discrimination capability of the scintillator that allows particle identification. We report a measurement of the annual modulation of the 7Be neutrino interaction rate. The period, the amplitude, and the phase of the observed modulation are consistent with the solar origin of these events, and the absence of their annual modulation is rejected with higher than 99% C.L. The physics implications of Phase-I results in the context of the neutrino oscillation physics and solar models are presented. [ABSTRACT FROM AUTHOR]

Water produced in a polymer electrolyte membrane (PEM) fuel cell enhances membrane proton conductivity; this positive feedback loop can lead to current ignition. Gas-phase convection and membrane diffusion of water coupled with water production in a simplified two-dimensional PEM fuel cell leads to localized ignition and current density front propagation in the cell. Co-current gas flow in the anode and cathode channels causes ignition at the cell outlet, and membrane diffusion causes the front to slowly propagate toward the inlet; counter-current flow in the anode and cathode channels causes ignition in the interior of the cell, with the current density fronts subsequently spreading toward both inlets. The basic chemistry and physics of the spatiotemporal nonlinear dynamics of the two-dimensional fuel cell current can be captured by extending a simple one-dimensional stirred tank reactor model to a “tanks-in-series” model.

Polystyrene−ethylene−butylene sulfonate copolymer membranes (PSEBS) were photochemically cross-linked using benzophenone as the photo-initiator. Benzophenone decomposed by first-order kinetics during the cross-linking process. The cross-linked PSEBS had lower water swelling, lower proton conductivity, and higher chemical stability than un-cross-linked PSEBS. The cross-linking process did not change the ion exchange capacity (IEC); the sulfonic acid groups were stable during the UV photo-cross-linking process. The photo-cross-linked PSEBS membranes degraded more slowly during fuel cell operation than non-cross-linked membranes. A layered membrane with PSEBS sandwiched between thin Nafion layers degraded at almost the same rate as PSEBS membranes. Nafion layer contacted with electrodes cannot prevent membrane from degradation during the fuel cell operation; degradation reaction carried out all through the membrane between cathode and anode.

Thiols can be selectively removed and recovered from a hydrocarbon stream by a heterogeneous reaction with oxides and hydroxides of Pb, Hg(II), and Ba. Alkanethiols of lengths n-C6, n-C8, and n-C12 were found to react with powdered metal oxides to form stable thiolates that are solid at room temperature and insoluble in aqueous and organic solvents. The reaction converts the solid oxide phase into a solid thiolate phase, removing ions from the surface of the oxide, allowing the reaction to reach completion. The thiolates can be removed from the feed stream by filtration. Once separated, the metal and the original thiols can be recovered by extraction with a dilute acid, yielding a metal salt in the aqueous phase and a hydrophobic layer of thiol. The choice of reactive metal oxides may be predicted from simple thermodynamic considerations.

The prototype of the Borexino detector Counting Test Facility, located in the Gran-Sasso laboratory, has been used to obtain a bound on the stability of the electron. The new lower limit on the mean lifetime defined on 32.1 days of data set is τ(e−→νe+γ)⩾4.6×1026yr (90% c.l.).

Bulk crystallinity of vanadyl(IV) pyrophosphate catalysts forn-butane partial oxidation increased up to 23 days on stream as determined by XRD and Raman spectroscopy, while selectivity reached steady state after 8–10 days. Electron microscopy detected a 15 Å amorphous layer terminating the (200) planes of (VO)2P2O7 in fresh catalysts that was not observed in the equilibrated catalysts. It is suggested that ordering of (200) planes at the surface of (VO)2P2O7 is responsible for selective oxidation.

FT-IR PAS measurements have been made of the optical properties of powdered samples at temperatures up to 350° C. These indicate that sample emission must be taken into account and that photoacoustic emission spectroscopy can be used to obtain spectral data. The experiments are discussed in terms of a model of an ideal FT-IR. It is shown that the high temperature spectra must be interpreted in terms of an absorption and sample emission signal that have a relative phase difference of 180°.

Abstract: A brief review of the solar neutrino observations is given. Future solar neutrino measurements are discussed. The use of an artificial neutrino source to be used with low threshold solar neutrino detectors is presented. At present the neutrino source is mainly planned for short baseline neutrino studies. [Copyright &y& Elsevier]

Abstract: This paper summarizes the main recent results of the Borexino experiment, a liquid scintillator neutrino detector of unprecedented radiopurity currently running at the Laboratori Nazionali del Gran Sasso in Italy. Particularly, the paper is focused on the precision measurement of the 7Be solar neutrino flux, on the search of its day–night modulation, and on the first detection of pep neutrinos. The paper also covers a recent measurement of the CNGS neutrinos speed made in May 2012. A short discussion about the forthcoming scientific program on solar neutrinos, geoneutrinos, and sterile neutrino searches is included at the end. [Copyright &y& Elsevier]

The Borexino experiment has been running since May 2007 at the Gran Sasso underground laboratory, in Italy. Solar neutrinos are detected with a large unsegmented liquid scintillator detector with unprecedented radioactive purity. The main results obtained include the measurement of the 7Be solar neutrino flux, the measurement of the 8B neutrino flux with electron recoil energy threshold of 3.0 MeV and the first clear detection of geo-neutrinos (see Aldo Ianniʼs talk in these proceedings for further details). Borexino has recently completed a large calibration campaign, and better results on 7Be solar neutrino measurement are expected soon. Short and medium term perspectives are summarized in the conclusions. [ABSTRACT FROM AUTHOR]

Borexino is a large-volume liquid scintillator detector placed in the underground halls of the Laboratori Nazionali del Gran Sasso in Italy. After several years of construction, data taking started in May 2007, providing immediately incontrovertible evidence of the unprecedented radiopurity of the target mass. Here we report on the newest Borexino results obtained with about 200 days of data. Borexino provides the first direct measurement of the solar neutrino survival probability in both vacuum-dominated and matter-enhanced regions provided by a single experiment. The interaction rate of the 0.862 MeV 7Be solar neutrinos is found to be counts/(day⋅100 tons), in agreement with the oscillation hypothesis in the MSW Large Mixing Angle scenario. The first real-time measurement of the 8B solar neutrinos above 2.8 MeV provides interaction rate of counts/(day⋅100 tons). These measurements improve the experimental determination of the flux of the pp and CNO solar neutrinos, and the limit on the effective magnetic moment using solar neutrinos. [Copyright &y& Elsevier]

Abstract: Borexino is a large-volume liquid scintillator experiment for low energy neutrino detection, operating since May 2007, and installed at the National Laboratory of Gran Sasso. Borexino is the first experiment able to observe in real-time Solar neutrino interactions also in the sub-MeV range. We report with this work the main results achieved in the Solar neutrino sector by Borexino. In particular, we report the results on the measured interaction rates of 7Be, 8B, and pep neutrinos, and their impacts on the physics of neutrino oscillations. [Copyright &y& Elsevier]

We report the measurement of the 8B solar neutrinos interaction rate with the Borexino detector. The extremly high radio-purity reached in the Borexino scintillator, combined with the efficient software rejection of cosmogenic background, allows to investigate the recoiled electron spectrum, induced by 8B solar neutrinos, down to the unprecedented energy threshold of 2.8 MeV. The rate of 8B solar neutrino interaction as measured through their scattering on the target electrons is c/d/100 tons. This corresponds to an equivalent electron neutrino flux of , as derived from the elastic scattering only, in good agreement with existing measurements and predictions. [Copyright &y& Elsevier]

Borexino, at the I.N.F.N. Gran Sasso Underground Laboratory in Italy, is an experiment designed to detect, in real-time, low energy solar neutrinos. After a brief presentation of the Borexino physics and detector, we illustrate some recent results and their physics implications. Borexino perspectives are also discussed. [ABSTRACT FROM AUTHOR]

The status of the BOREXINO experiment is presented. The physics potential of the experiment is reviewed. [Copyright &y& Elsevier]