arXiv subjects

Francesco Vissani

Publications and source records attributed to Francesco Vissani.

At least 37 records · Page 2Linked to original sources

arXiv2021

What is matter according to particle physics and why try to observe its creation in lab

The standard model of elementary interactions has long qualified as a theory of matter, in which the postulated conservation laws (one baryonic and three leptonic) acquire theoretical meaning. However, recent observations of lepton number violations -- neutrino oscillations -- demonstrate its incompleteness. We discuss why these considerations suggest the correctness of Ettore Majorana's ideas on the nature of neutrino mass, and add further interest to the search for an ultra-rare nuclear process in which two particles of matter (electrons) are created, commonly called neutrinoless double beta decay. The approach of the discussion is mainly historical and its character is introductory. Some technical considerations, which highlight the usefulness of Majorana's representation of gamma matrices, are presented in the appendix.

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arXiv2020

On the energy of the protons producing the very high-energy astrophysical neutrinos

We study the distribution of the energy of the protons that can produce an astrophysical neutrino with a given observed energy, in the TeV--PeV range, both through $pp$ or $pγ$ interactions. Due to the increasing multiplicity of the pion production at high center of mass energies, the resulting average proton energies can be much larger than the often used approximate value $E_p\simeq 20E_ν$. Also the threshold of the $pγ$ process can lead to a pronounced increase in the values of $\langle E_p\rangle /E_ν$ for decreasing neutrino energies. The results depend sensitively on the assumed proton spectrum, since steeper spectra give less weight to the lower energy neutrino tail resulting from the decays of the abundant low-energy pions. In the $pγ$ scenarios they also depend sensitively on the spectrum of the target photons. The results are in particular relevant to relate possible characteristics of the neutrino spectrum to those of the corresponding cosmic rays that generated them. We also discuss the associated production of gamma rays at the sources.

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arXiv2020

The formalism of neutrino oscillations: an introduction

The recent wide recognition of the existence of neutrino oscillations concludes the pioneer stage of these studies and poses the problem of how to communicate effectively the basic aspects of this branch of science. In fact, the phenomenon of neutrino oscillations has peculiar features and requires to master some specific idea and some amount of formalism. The main aim of these introductory notes is exactly to cover these aspects, in order to allow the interested students to appreciate the modern developments and possibly to begin to do research in neutrino oscillations.

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arXiv2020

The luminosity constraint in the era of precision solar physics

The luminosity constraint is a very precise relationship linking the power released by the Sun as photons and the solar neutrino fluxes. Such a relation, which is a direct consequence of the physical processes controlling the production and the transport of energy in the solar interior, is of great importance for the studies of solar neutrinos and has a special role for the search of neutrinos from the CNO cycle, whose first detection with a 5$σ$ significance has been recently announced by the Borexino collaboration. Here we revise the luminosity constraint, discussing and validating its underlying hypotheses, in the light of latest solar neutrino and luminosity measurements. We generalize the current formulation of the luminosity constraint relation so that it can be easily used in future analysis of solar neutrino data, and we provide a specific application showing the link between CNO and pp neutrino fluxes.

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arXiv2020

On the rate of core collapse supernovae in the Milky Way

Several large neutrino telescopes, operating at various sites around the world, have as their main objective the first detection of neutrinos emitted by a gravitational collapse in the Milky Way. The success of these observation programs depends on the rate of supernova core collapse in the Milky Way, $R$. In this work, standard statistical techniques are used to combine several independent results. Their consistency is discussed and the most critical input data are identified. The inference on $R$ is further tested and refined by including direct information on the occurrence rate of gravitational collapse events in the Milky Way and in the Local Group, obtained from neutrino telescopes and electromagnetic surveys. A conservative treatment of the errors yields a combined rate $R=1.63 \pm 0.46$ (100 yr)$^{-1}$; the corresponding time between core collapse supernova events turns out to be $T=61_{-14}^{+24}$~yr. The importance to update the analysis of the stellar birthrate method is emphasized.

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arXiv2020

Neutrino telescopes and high-energy cosmic neutrinos

In this review paper, we present the main aspects of high-energy cosmic neutrino astrophysics. We begin by describing the generic expectations for cosmic neutrinos, including the effects of propagation from their sources to the detectors. Then we introduce the operating principles of current neutrino telescopes, and examine the main features (topologies) of the observable events. After a discussion of the main background processes, due to the concomitant presence of secondary particles produced in the terrestrial atmosphere by cosmic rays, we summarize the current status of the observations with astrophysical relevance that have been greatly contributed by IceCube detector. Then, we examine various interpretations of these findings, trying to assess the best candidate sources of cosmic neutrinos. We conclude with a brief perspective on how the field could evolve within a few years.

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arXiv2019

Empirical inference on the Majorana mass of the ordinary neutrinos

There is a broad theoretical consensus on the idea that ordinary neutrinos have a Majorana mass, but we have no clear prediction about its value, and direct experimental measurements of this quantity are rather challenging. In this work, we argue that the current cosmological measurements allow us to obtain precise information on the effective Majorana mass, i.e. the electronic-type mass of ordinary neutrinos. We show that the numerical results that we obtain can be accurately reproduced, and hence tested, by a straightforward analytical procedure. We then discuss the stability of the assumptions at the basis of our analysis and the implications of our findings for neutrinoless double beta decay.

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arXiv2019

On the relevance of prompt neutrinos for the interpretation of the IceCube signals

The IceCube collaboration has discovered a new, cosmic component of high-energy neutrinos. Although neutrino oscillations suggest that the cosmic neutrino spectrum is almost the same for every neutrino flavor, the attempts to reconstruct it, based on different analyses, lead to different energy spectra below 100 TeV. In this work, we propose a phenomenological model that, assuming collisions between cosmic rays and hadrons as the production mechanism of high-energy neutrinos, yields quantitative expectations for each neutrino flavor. We discuss the detectability of the prompt component of the atmospheric neutrino spectrum, pointing out the most relevant dataset, which has to be muon-neutrino depleted and to cover the energy region 10-100 TeV. We argue that the prompt component can cause the spectral difference between the High-Energy-Starting-Event (HESE) and the through-going muon datasets. Finally, we point out the need for adopting a consistent model for the interpretation of the data, stressing that a separate treatment of the different datasets is, by converse, a suboptimal procedure.

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arXiv2018

Luminosity constraint and entangled solar neutrino signals

The current frontier of solar neutrino physics is the observation of CNO neutrinos. The signals of CNO and PP neutrinos are however entangled: In fact, the pp-flux can be known precisely only if CNO-flux is quantified; the interpretation of the gallium experiments depends upon both fluxes; a precise knowledge of pep-flux is a precondition to extract the CNO-neutrino signal with Borexino. The luminosity constraint plays an increasingly important rôle: we present it in a new form, improving the expression obtained by J. Bahcall in Phys. Rev. C 65 (2002) 025801.

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arXiv2018

On the capture rates of big bang neutrinos by nuclei within the Dirac and Majorana hypotheses

The capture rates of non-relativistic neutrinos on beta decaying nuclei depends on whether their mass is Dirac or Majorana. It is known that for relic neutrinos from the big-bang, and within minimal assumptions, the rate is a factor two larger in the Majorana case. We show that this difference also depends on the value of the lightest neutrino mass and on the type of mass hierarchy. If the lightest neutrino has a mass below the meV, so that it is still relativistic today, its capture rate for the case of Dirac masses becomes equal to that for Majorana masses. As a consequence, for the case of normal neutrino mass hierarchy, for which the total capture rate is dominated by the contribution from the lightest neutrino, if this one is below the meV the distinction between the Dirac and Majorana scenarios can only rely on the detection of the two heavier neutrinos, which is something very challenging.

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arXiv2018

Introduction to neutrino astronomy

This writeup is an introduction to neutrino astronomy, addressed to astronomers and written by astroparticle physicists. While the focus is on achievements and goals in neutrino astronomy, rather than on the aspects connected to particle physics, we will introduce the particle physics concepts needed to appreciate those aspects that depend on the peculiarity of the neutrinos. The detailed layout is as follows: In Sect.~1, we introduce the neutrinos, examine their interactions, and present neutrino detectors and telescopes. In Sect.~2, we discuss solar neutrinos, that have been detected and are matter of intense (theoretical and experimental) studies. In Sect.~3, we focus on supernova neutrinos, that inform us on a very dramatic astrophysical event and can tell us a lot on the phenomenon of gravitational collapse. In Sect.~4, we discuss the highest energy neutrinos, a very recent and lively research field. In Sect.~5, we review the phenomenon of neutrino oscillations and assess its relevance for neutrino astronomy. Finally, we offer a brief overall assessment and a summary in Sect.~6. The material is selected - i.e., not all achievements are reviewed - and furthermore it is kept to an introductory level, but efforts are made to highlight current research issues. In order to help the beginner, we prefer to limit the list of references, opting whenever possible for review works and books.

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arXiv2018

The importance of observing astrophysical tau neutrinos

The evidence of a new population of diffuse high-energy neutrinos, obtained by IceCube, has opened a new era in the field of neutrino physics. Up to now the events detected are still without any source counterpart. The detected events are compatible with the standard picture of cosmic neutrinos undergoing 3-flavor neutrino oscillations. We analyze the implications of neutrino oscillations for the present and future experiments, focusing particularly on tau neutrinos. In fact tau neutrinos are very important: even if they are not produced in astrophysical sites, they have to exist due to oscillations and their observation should be regarded as a basic proof in support of this scenario. Moreover, IceCube's measurement of the flux of muon neutrinos implies that the flux of tau neutrinos is measured within $20\%$, just assuming standard neutrino oscillations. On this basis, after discussing the experimental signatures of tau neutrinos, we predict the rates for $ν_τ$ detection in the present and future neutrino telescopes. We show that the present IceCube detector is close to observe the first tau neutrinos, with a probability of about 90\%. Moreover the next generation of IceCube can identify about 2 neutrinos per year, reaching an evidence of 5$σ$ in about 10 years, despite the present uncertainty on the spectrum and on the production mechanism. The non observation of these neutrino events would have dramatic implications, such as the questioning of cosmic neutrino observations or the violation of neutrino oscillations over cosmological scales.

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arXiv2018

Supernova neutrino physics with a nuclear emulsion detector

The existence of the coherent neutrino-nucleus scattering reaction requires to evaluate, for any detector devoted to WIMP searches, the irreducible background due to conventional neutrino sources and at same time, it gives a unique chance to reveal supernova neutrinos. We report here a detailed study concerning a new directional detector, based on the nuclear emulsion technology. A Likelihood Ratio test shows that, in the first years of operations and with a detector mass of several tens of tons, the observation of the supernova signal can be achieved. The determination of the distance of the supernova from the neutrinos and the observation of $^8$B neutrinos are also discussed.

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arXiv2017

Joint analysis of Borexino and SNO solar neutrino data and reconstruction of the survival probability

Solar neutrino oscillations are supported by KamLAND's antineutrino measurements, but certain solar neutrino data - the observed shape of the ${}^8$B flux and the difference between day and night counting rates measured in Super-Kamiokande - do not fit well with the ensuing oscillation pattern. Interestingly, other solar neutrino data allow independent tests of the survival probability. Thanks to the new measurements of Borexino at low-energies along with the standard solar model and to the results of SNO at high-energies, four values of the neutrino survival probability are known. We build and study a likelihood based only on these solar neutrino data. The results agree well with the standard oscillation pattern and in particular with KamLAND findings. A related and straightforward procedure permits to reconstruct the survival probability of solar neutrinos and to assess its uncertainties, for all solar neutrino energies.

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arXiv2017

What can we learn on supernova neutrino spectra with water Cherenkov detectors?

We investigate the precision with which the supernova neutrino spectra can be reconstructed in water Cherenkov detectors, in particular the large scale Hyper-Kamiokande and Super-Kamiokande. To this aim, we consider quasi-thermal neutrino spectra modified by the Mikheev-Smirnov-Wolfenstein effect for the case of normal ordering. We perform three 9 degrees of freedom likelihood analyses including first inverse-beta decay only, then the combination of inverse beta decay and elastic scattering on electrons and finally a third analysis that also includes neutral scattering neutrino-oxygen events. A tenth parameter is added in the analyses to account for the theoretical uncertainty on the neutral current neutrino-oxygen cross section. By assuming a 100\% efficiency in Hyper-Kamiokande, we show that one can reconstruct the electron antineutrino average energy and pinching parameter with an accuracy of $\sim2\%$ and $\sim7\%$ percent respectively, while the antineutrino integrated luminosity can be pinned down at $\sim3\%$ percent level. As for the muon and tau neutrinos, the average energy and the integrated luminosity can be measured with $\sim7\%$ precision. These results represent a significant improvement with respect Super-Kamiokande, particularly for the pinching parameter defining the electron antineutrino spectra. As for electron neutrinos, the determination of the emission parameters requires the addition of supplementary detection channels.

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arXiv2017

Measuring the neutron star compactness and binding energy with supernova neutrinos

We investigate the precision with which a neutron star gravitational binding energy can be measured through the supernova neutrino signal, without assuming any prior such as the energy equipartition hypothesis, mean energies hierarchy or constraints on the pinching parameters that characterize the neutrino spectra. We consider water Cherenkov detectors and prove that combining inverse beta decay with elastic scattering on electrons is sufficient to reach $11\%$ precision on the neutron star gravitational binding energy already with Super-Kamiokande. The inclusion of neutral current events on oxygen in the analysis does not improve the precision further. We show that $3\%$ precision can be achieved if priors are introduced, such as energy equipartition. We discuss the implications of our findings on the properties of the newly formed neutron star, in particular concerning the assessment of the compactness or mass--radius relation.

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arXiv2017

Testing creation of matter with neutrinoless double beta decay

In this brief review, the importance of the so called neutrinoless double beta decay transition in the search for physics beyond the Standard Model is emphasized. The expectations for the transition rate are examined in the assumption that ordinary neutrinos have Majorana masses. We stress the relevance of cosmological measurements and discuss the uncertainties implied by nuclear physics.

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arXiv2017

On the compatibility of the IceCube results with an universal neutrino spectrum

There is mounting evidence that the IceCube findings cannot be described simply invoking a single power-law spectrum for cosmic neutrinos. We discuss which are the minimal modifications of the spectrum that are required by the existing observations and we obtain a universal cosmic neutrino spectrum, i.e. valid for all neutrino flavors. Our approach to such task can be outlined in three points: 1) we rely on the throughgoing muon analysis above 200 TeV and on the high-energy starting events (HESE) analysis below this energy, requiring the continuity of the spectrum; 2) we assume that cosmic neutrinos are subject to three-flavor neutrino oscillations in vacuum; 3) we make no assumption on the astrophysical mechanism of production, except for no tau neutrino component at the source. We test our model using the information provided by HESE shower-like events and by the lack of double pulses and resonant events. We find that a two power-law spectrum is compatible with all observations. The model agrees with the standard picture of pion decay as a source of neutrinos, and indicates a slight preference for a pgamma mechanism of production. We discuss the tension between the HESE and the throughgoing muons datasets around few tens TeV, focussing on the angular distributions of the spectra. The expected number of smoking-gun signatures of nu-tau induced events (referred to as double pulses) is quantified: in the baseline model we predict 0.65 double pulse events in 5.7 years. Uncertainties in the predictions are quantified.

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