1,721,195 research outputs found
Looking inside the Sun with the Borexino experiment: detection of solar neutrinos from the proton-proton chain and the CNO cycle
No full textThe Sun is fueled by fusion processes occurring in its core that convert hydrogen into helium. Photons produced in these reactions take an order of billion years to reach the surface. However, there is another byproduct of nuclear fusion: neutrinos. They are light and electrically neutral, and, unlike photons, escape the Sun in a matter of seconds. These so-called solar neutrinos are the only carriers of real-time information about the core of our Star. We know that at least 99% of solar energy is generated through the proton-proton (pp) fusion chain. One more process through which hydrogen-to-helium fusion may occur is the catalytic carbon-nitrogen-oxygen (CNO) cycle. As it is hypothesized to be the main source of energy in heavier stars, its discovery would carry implications in astrophysics, and provide insights about the chemical composition of the core of the Sun, which is not yet fully understood. Moreover, we can exploit this intense natural beam of neutrinos radiated by the Sun to study the phenomenon of neutrino oscillation, the discovery of which was achieved thanks to solar neutrino data. The Borexino detector was designed with the primary goal of detecting the so-called Be neutrinos, originating from the pp chain. It is particularly suitable for solar neutrino measurement due to its unprecedented radiopurity and resolution at low energies. After ten years of data taking, the Borexino experiment has comprehensively studied all pp-chain neutrinos, not only fulfilling but even surpassing its purpose. This thesis presents the results and implications of this measurement, as well as the analysis behind it. The next milestone of Borexino was to probe the existence of the CNO cycle in the Sun through the detection of neutrinos produced in it. I will describe my work on the methods of monitoring the evolution of the detector and improving the quality of its data, which was deemed crucial for the CNO neutrino analysis. Concluding my thesis, I will present the analysis methods and preliminary results, which show evidence of the existence of CNO neutrinos. The work described in this thesis and my accomplishments are achieved thanks to the collective effort of the Borexino collaboration
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Updated geoneutrino measurement with Borexino
No full textThere are still several unanswered fundamental questions concerning our planet and in particular, about the deep Earth, from where we lack direct samples. Today, thanks to the progress in neutrino-detection techniques, geoneutrinos, antineutrinos from the decays of long-lived radioactive elements inside the Earth, can be exploited as a new and unique tool to study our planet. Borexino has presented its latest geoneutrino measurement in 2015. Thanks to both more acquired data, as well as to improved analysis techniques in an enlarged fiducial volume, we provide an updated measurement with significantly improved precision. The talk will describe the key elements of the updated analysis and will present the measured geoneutrino signal. Geological interpretation and significance of the new result will be discussed, as for example in terms of the corresponding radiogenic heat, geoneutrino signal from the Earth’s mantle or the limit to the hypothetical georeactor. The talk is presented in the name of Borexino Collaboration
Overview of experimental results on geoneutrinos
No full textThanks to the progress in neutrino-detection techniques, geoneutrinos, antineutrinos from the decays of long-lived radioactive elements inside the Earth, can be detected and exploited as a unique tool to study our planet. Geoneutrinos from the 238U and 232Th radioactive chains with energies above 1.8 MeV were measured by the KamLAND experiment in Japan and the Borexino experiment in Italy, exploiting the charge-current inverse-beta decay interaction on protons. Both detectors are located underground and feature large volume liquid scintillator target. The most relevant backgrounds to geoneutrino measurement are represented by reactor antineutrinos, residual muon flux, and intrinsic radioactivity of the detector. Both experiments reached similar precision of the geoneutrino signal measurement in the range of 15 to 18% and confirmed a general consistency of the measured signal with the geological expectations. Due to the different geological settings and geographical locations, their results are complementary. Assuming a laterally homogeneous mantle, their measurements feature some level of tension: Borexino prefers geological models predicting higher U and Th abundances, while KamLAND favors their lower abundances. The talk will describe the key elements of the analysis, overview of the latest results and their geological interpretation, in terms of the corresponding radiogenic heat, geoneutrino signal from the Earth's mantle, and the limit to the hypothetical georeactor
Optimization of a neutrino beam for the study of CP violation with the LENA and JUNO detector
No full textOptimization of a neutrino beam for the study of CP violation with the LENA and JUNO detectorsNeutrino beams are nowadays a commonly used and well investigated tool to study neutrino oscillations, e.g. T2K, NOνA experiments. Beam neutrinos are produced by the decays of properly focused particles - mostly pions and kaons - generated by the collisions of accelerated protons with a target. The shape and composition of the obtained neutrino fluxes depend on the properties of the neutrino production apparatus. Primary beam, target, focusing system and decay tunnel must be optimized relatively to the neutrino detector, in order to achieve the highest possible sensitivity to oscillation parameters such as the CP-violating phase δ_CP.This work focuses on the use of genetic algorithm for the optimization of simulated neutrino beams to the liquid scintillator neutrino detectors LENA (50kt), proposed in the Pyhäsalmi mine in Finland, and JUNO (20kt), under construction in Jiangmen, China, respectively from the European Spallation Source (ESS) in Lund, Sweden, and from the China Spallation Neutron Source in Dongguan, China.As a result of the neutrino beam simulation and optimization, δ_CP=0 or δ_CP=π could be excluded by LENA with a 3σ sensitivity for ~56% of the whole δ_CP range at the chosen baseline; for JUNO the maximum value reached by the test statistics would be around ∆χ^2 ~ 6
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