Search

Over the last decade breakthrough neutrino results came from Borexino, a massive, calorimetric liquid scintillator detector installed at the underground Gran Sasso Laboratory. With its unprecedented radiopurity levels attained in the core of the detection medium, it was, until it took data, the only experiment able to study in real time solar neutrino interactions in the challenging sub-MeV energy region. The recently achieved outstanding first observation of the CNO flux is thoroughly described in this work. Its other results in the solar neutrino field are remined, namely the first real time, spectroscopic measurement of the flux, the precise measurement of the Be flux, the high significance flux observation, and the measurement of the B neutrino spectrum. Such an impressive series of outputs makes Borexino the only experiment operated so far which was able to perform the full solar neutrino spectroscopy. The physics implications in the realm of neutrino oscillations stemming from the plethora of Borexino outputs is also illustrated. [ABSTRACT FROM AUTHOR]

After publication we discovered that some entries in table 2 and the corresponding contours in figures 3 and 4 have been misprinted. We provide here the correct version of table 2 and figures 3 and 4. The discussion and conclusions in the text of the paper remain unchanged. [ABSTRACT FROM AUTHOR]

We present the results of a new analysis of the data of the MiniBooNE experiment taking into account the additional background of photons from ∆+/0 decay proposed in ref. [1] and additional contributions due to coherent photon emission, incoherent production of higher mass resonances, and incoherent non-resonant nucleon production. We show that the new background can explain part of the MiniBooNE low-energy excess and the statistical significance of the MiniBooNE indication in favor of short-baseline neutrino oscillation decreases from 5.1σ to 3.6σ. We also consider the implications for short-baseline neutrino oscillations in the 3+1 active-sterile neutrino mixing framework. We show that the new analysis of the MiniBooNE data indicates smaller active-sterile neutrino mixing and may lead us towards a solution of the appearance-disappearance tension in the global fit of short-baseline neutrino oscillation data. [ABSTRACT FROM AUTHOR]

A fundamental breakthrough which opened the way to the realization of the Borexino detector was the demonstration of exceptionally low, unprecedented radioactive contaminations in the liquid scintillator, obtained with its pilot prototype Counting Test Facility. Though of limited dimension, with its 4.8 m3 of active liquid core, CTF has however been a key milestone not only for Borexino, but also for the entire field of the ultra-low background searches. Here, we succinctly remind the motivations, which concurred to lay down the project, as well as the specific radiopurity challenge, which guided the design. After the description of the technical elements of the detector, the main outcomes are summarized, both regarding optical and purity scintillator properties, with special emphasis on the exceptional achievements in term of ultra-low traces of radioactive contaminants. The discussion is completed with the description of how CTF was employed for the pre-qualification of the entire inventory of the Borexino scintillator, confirming also in the final phase of its life its essential role for the success of the overall Borexino solar neutrino program. [ABSTRACT FROM AUTHOR]

In the last decades, a very important breakthrough has been brought about in the elementary particle physics by the discovery of the phenomenon of the neutrino oscillations, which has shown neutrino properties beyond the Standard Model. But a full understanding of the various aspects of the neutrino oscillations is far to be achieved. In this paper the theoretical background of the neutrino oscillation phenomenon is described, referring in particular to the paradigmatic models. Then the various techniques and detectors which studied neutrinos from different sources are discussed, starting from the pioneering ones up to the detectors still in operation and to those in preparation. The physics results are finally presented adopting the same research path which has been crossed by this long saga. Theproblems not yet fixed in this field are discussed, together with the perspectives of their solutions in the near future. [ABSTRACT FROM AUTHOR]

Summary: The neutrino oscillation is one of the most important insights of the last decades in the physics of the elementary particles. The study of the solar neutrinos has been of fundamental importance in understanding the neutrino experimental behavior. The Standard Solar Model is the unavoidable basis and the MSW effect the most important hypothesis for this study. After the pioneering radiochemical data and the Cherenkov experiments, which have given the first proof of the oscillation in the solar-neutrino sector, Borexino succeeded to extend the study to almost the entire spectrum of the solar neutrinos, being a unique experiment able to detect in real time the neutrino interactions down to ~ 200 keV, thanks to its unprecedented radio-purity. In this way the analysis of the oscillations has been extended to the vacuum regime, while the shape of the transition region vacuum-matter has to be refined after the first Borexino results. This study is carried on exploiting the upgraded performances of the detector, while other experiments in construction or in design phase will adress the same problem. [ABSTRACT FROM AUTHOR]

Pulse shape discrimination is one of the more distinctive features of liquid scintillators. However, the optimum discrimination method to distinguish different types of particles, described in the seminal paper of Gatti and De Martini of more than 40 years ago, was not suitable for routine application until the recent development of adequately fast sampling techniques. In this work we present the features of a board explicitly designed and realized to exploit the performance of a fast, high resolution, 10-bit flash analog-to-digital converter (ADC) in order to sample with sufficient accuracy the integrated scintillation waveforms obtained under alpha or beta irradiation of a scintillator specimen. Data samples could then be processed according to the Gatti and De Martini method (modified following the prescription of Jordanov and Knoll in the case of integrated pulses) to quantify the optimum separation achievable. The board, besides providing the integration of the pulse within its analog portion and the digitization of the signal in the digital section, is also equipped with useful auxiliary functions that increase its versatility and practical operability. Using the same scintillator-phototube assembly, experimental pulse shape discrimination measurements were obtained with the new board and with the conventional charge technique and those results are illustrated here. Output from a Monte Carlo model allowed us to perform a numerical comparison of the performance of the optimum method versus the conventional one. [ABSTRACT FROM AUTHOR]

The measured characteristics of 2200 photomultiplier tubes (PMTs) for the future Borexino experiment are considered to provide the most complete information for evaluating the time characteristics of ETL9351 PMTs with a high precision. The unique time characteristics of the apparatus used and the large statistics obtained during the tests of the PMTs allow the fine structure of the PMT time response to be resolved. A method for obtaining the probability density function of the single-photoelectron counting from the experimental data is proposed and used to derive the PMT average characteristics. For the first time, an analytical model is proposed to describe all the features of the single-photoelectron PMT time response. The origin of small-amplitude pulses, as well as the shape of the time spectra of PMT, is explained. [ABSTRACT FROM AUTHOR]