arXiv subjects

E. Lisi

Publications and source records attributed to E. Lisi.

At least 91 records · Page 5Linked to original sources

arXiv1998

Super-Kamiokande atmospheric neutrino data, zenith distributions, and three-flavor oscillations

We present a detailed analysis of the zenith angle distributions of atmospheric neutrino events observed in the Super-Kamiokande (SK) underground experiment, assuming two-flavor and three-flavor oscillations (with one dominant mass scale) among active neutrinos. In particular, we calculate the five angular distributions associated to sub-GeV and multi-GeV μ-like and e-like events and to upward through-going muons, for a total of 30 accurately computed observables (zenith bins). First we study how such observables vary with the oscillation parameters, and then we perform a fit to the experimental data as measured in SK for an exposure of 33 kTy (535 days). In the two-flavor mixing case, we confirm the results of the SK Collaboration analysis, namely, that ν_μ<--->ν_τoscillations are preferred over ν_μ<--->ν_e, and that the no oscillation case is excluded with high confidence. In the three-flavor mixing case, we perform our analysis with and without the additional constraints imposed by the CHOOZ reactor experiment. In both cases, the analysis favors a dominance of the ν_μ<--->ν_τchannel. Without the CHOOZ constraints, the amplitudes of the subdominant ν_μ<--->nu_e and ν_e<--->ν_τtransitions can also be relatively large, indicating that, at present, current SK data do not exclude sizable ν_e mixing by themselves. After combining the CHOOZ and SK data, the amplitudes of the subdominant transitions are constrained to be smaller, but they can still play a nonnegligible role both in atmospheric and other neutrino oscillation searches. In particular, we find that the ν_e appearance probability expected in long baseline experiments can reach the testable level of ~15%.

hep-ph↗

arXiv1998

Solar neutrino interactions: Using charged currents at SNO to tell neutral currents at Super-Kamiokande

In the presence of flavor oscillations, muon and tau neutrinos can contribute to the Super-Kamiokande (SK) solar neutrino signal through the neutral current process ν_{μ,τ} e^{-}\to ν_{μ,τ} e^{-}. We show how to separate the ν_e and ν_{μ,τ} event rates in SK in a model independent way, by using the rate of the charged current process ν_e d \to p p e^{-} from the Sudbury Neutrino Observatory (SNO) experiment, with an appropriate choice of the SK and SNO energy thresholds. Under the additional hypothesis of no oscillations into sterile states, we also show how to determine the absolute ^{8}B neutrino flux from the same data set, independently of the ν_e survival probability.

hep-ph↗

arXiv1998

Quantifying uncertainties in primordial nucleosynthesis without Monte Carlo simulations

We present a simple method for determining the (correlated) uncertainties of the light element abundances expected from big bang nucleosynthesis, which avoids the need for lengthy Monte Carlo simulations. Our approach helps to clarify the role of the different nuclear reactions contributing to a particular elemental abundance and makes it easy to implement energy-independent changes in the measured reaction rates. As an application, we demonstrate how this method simplifies the statistical estimation of the nucleon-to-photon ratio through comparison of the standard BBN predictions with the observationally inferred abundances.

astro-ph↗

arXiv1998

Vacuum oscillations and variations of solar neutrino rates in SuperKamiokande and Borexino

The vacuum oscillation solution to the solar neutrino problem predicts characteristics variations of the observable neutrinos rates, as a result of the L/E_nu dependence of the nu_e survival probability (L and E_nu being the neutrino pathlength and energy, respectively). The E_nu-dependence can be studied through distortions of the recoil electron spectrum in the SuperKamiokande experiment. The L-dependence can be investigated through a Fourier analysis of the signal in the SuperKamiokande and Borexino experiments. We discuss in detail the interplay among such observable variations of the signal, and show how they can help to test and constrain the vacuum oscillation solution(s). The analysis includes the 374-day SuperKamiokande data.

hep-ph↗

arXiv1998

Discriminating MSW solutions to the solar neutrino problem with flux-independent information at SuperKamiokande and SNO

The two possible Mikheyev-Smirnov-Wolfenstein (MSW) solutions of the solar neutrino problem (one at small and the other at large mixing angle), up to now tested mainly through absolute neutrino flux measurements, require flux-independent tests both for a decisive confirmation and for their discrimination. To this end, we perform a joint analysis of various flux-independent observables that can be measured at the SuperKamiokande and Sudbury Neutrino Observatory (SNO) experiments. In particular, we analyze the recent data collected at SuperKamiokande after 374 days of operation, work out the corresponding predictions for SNO, and study the interplay between SuperKamiokande and SNO observables. It is shown how, by using only flux-independent observables from SuperKamiokande and SNO, one can discriminate between the two MSW solutions and separate them from the no oscillation case.

hep-ph↗

arXiv1997

Zenith distribution of atmospheric neutrino events and electron neutrino mixing

Assuming atmospheric neutrino oscillations with dominant nu_mu<--->nu_tau transitions, we discuss how subdominant nu_e mixing (within the Chooz reactor bounds) can alter the zenith distributions of neutrino-induced electrons and muons. We isolate two peculiar distortion effects, one mainly related to nu_e mixing in vacuum and the other to matter oscillations, that may be sufficiently large to be detected by the SuperKamiokande atmospheric nu experiment. These effects (absent for pure two-flavor nu_mu<--->nu_tau transitions) do not vanish in the limit of energy-averaged oscillations.

hep-ph↗

arXiv1997

The solar neutrino problem after three hundred days of data at SuperKamiokande

We present an updated analysis of the solar neutrino problem in terms of both Mikheyev-Smirnov-Wolfenstein (MSW) and vacuum neutrino oscillations, with the inclusion of the preliminary data collected by the SuperKamiokande experiment during 306.3 days of operation. In particular, the observed energy spectrum of the recoil electrons from 8B neutrino scattering is discussed in detail and is used to constrain the mass-mixing parameter space. It is shown that: 1) the small mixing MSW solution is preferred over the large mixing one; 2) the vacuum oscillation solutions are strongly constrained by the energy spectrum measurement; and 3) the detection of a possible semiannual modulation of the 8B νflux due to vacuum oscillations should require at least one more year of operation of SuperKamiokande.

hep-ph↗

arXiv1997

Upward-going muons and neutrino oscillations

The available upward-going muon data from the Kamiokande, Baksan, MACRO, IMB, and SuperKamiokande experiments are reviewed and combined. Bounds on the neutrino mass and mixing parameters are derived for oscillations in two and three flavors. These bounds are not in significant conflict with the oscillation solution to the atmospheric neutrino flavor anomaly observed in the sub-GeV and multi-GeV energy range. The combination of all the available atmospheric data tends to favor the nu_mu <---> nu_e channel with respect to the nu_mu <---> nu_tau channel, and to disfavor the threefold maximal mixing scenario.

hep-ph↗

arXiv1997

Reconciling solar and terrestrial neutrino oscillation evidences with minimum sacrifice

The present possible evidences in favor of neutrino masses and mixings from solar, atmospheric, and accelerator experiments cannot be all reconciled in a three-family framework, unless some data are excluded. We grade all possible three-family scenarios according to their compatibility with the available data. A recently proposed scenario appears to emerge naturally as the most likely solution to all oscillation evidences, with the only exception of the angular dependence of multi-GeV atmospheric data in the Kamiokande experiment. We describe in detail the status and the phenomenological implications of this ``minimum sacrifice'' solution.

hep-ph↗

arXiv1997

Fourier analysis of real-time, high-statistics solar neutrino observations

Solar neutrino oscillations with wavelengths comparable to the Earth-Sun distance provide a viable explanations of the long-standing solar neutrino deficit. They imply a time-dependent modulation of the solar neutrino flux due to the eccentricity of the Earth orbit. Motivated by this testable prediction, we propose a Fourier analysis of the signal observable in real-time, solar neutrino experiments. We give the general expressions of the Fourier coefficients and of their correlated uncertainties in the presence of background. The expressions assume a particularly compact form in the case of two-flavor neutrino oscillations in vacuum. We discuss the sensitivity to the lowest harmonics of the new-generation, high-statistics experiments SuperKamiokande, Sudbury Neutrino Observatory, and Borexino.

hep-ph↗

arXiv1997

Muon-anti-neutrino <---> electron-anti-neutrino mixing: analysis of recent indications and implications for neutrino oscillation phenomenology

We reanalyze the recent data from the Liquid Scintillator Neutrino Detector (LSND) experiment, that might indicate anti-nu_mu<--->anti-nu_e mixing. This indication is not completely excluded by the negative results of established accelerator and reactor neutrino oscillation searches. We quantify the region of compatibility by means of a thorough statistical analysis of all the available data, assuming both two-flavor and three-flavor neutrino oscillations. The implications for various theoretical scenarios and for future oscillation searches are studied. The relaxation of the LSND constraints under different assumptions in the statistical analysis is also investigated.

hep-ph↗

arXiv1996

Neutrino Oscillations and Moments of Electron Spectra

We show that the effects of neutrino oscillations on 8B solar neutrinos are described well by the first two moments (the average and the variance) of the energy distribution of scattered or recoil electrons. For the SuperKamiokande and the Sudbury Neutrino Observatory experiments, the differences between the moments calculated with oscillations and the standard, no-oscillation moments are greater than 3 standard deviations for a significant fraction of the neutrino mass-mixing (Delta m^2, sin^2 2 theta) parameter space.

nucl-ex↗

arXiv1996

Indications from Precision Electroweak Physics Confront Theoretical Bounds on the Mass of the Higgs Boson

An updated fit to the precision electroweak data and to the direct measurement of the top quark mass $m_t$ provides significant constraints on $m_t$ and on the Higgs boson mass $M_H$: $m_t/\text{GeV}=172\pm 6$ and $\log_{10}(M_H/\text{GeV})=2.16\pm 0.33$, with an error correlation $ρ=0.5$. We integrate the $(M_H, m_t)$ probability distribution found in this analysis over various zones of the $(M_H, m_t)$ plane defined by one-sided experimental and theoretical bounds on the Higgs boson mass, both in the Standard Model and in its minimal supersymmetric extension. The comparison of the cumulative probabilities gives interesting information on the likelihood that the true value of $M_H$ is compatible with different theoretical scenarios.

hep-ph↗

arXiv1996

Solar neutrinos: Near-far asymmetry and just-so oscillations

We propose to study possible signals of just-so oscillations in new-generation solar neutrino experiments by separating the events detected when the earth is nearest to the sun (perihelion $\pm$~3~months) from those detected when the earth is farthest from the sun (aphelion $\pm$~3~months). We introduce a solar model independent near-far asymmetry, which is non-zero if just-so oscillations occur. We apply our calculations to the kinetic energy spectra of electrons induced by $^8$B solar neutrino interactions in the SuperKamiokande and Sudbury Neutrino Observatory experiments. We show that the sensitivity to the neutrino oscillation parameters can be increased by probing the near-far asymmetry in selected parts of the electron energy spectra.

hep-ph↗

arXiv1996

Tests of electron flavor conservation with the Sudbury Neutrino Observatory

We analyze tests of electron flavor conservation that can be performed at the Sudbury Neutrino Observatory (SNO). These tests, which utilize $^8$B solar neutrinos interacting with deuterium, measure: 1) the shape of the recoil electron spectrum in charged-current (CC) interactions (the CC spectrum shape); and 2) the ratio of the number of charged current to neutral current (NC) events (the CC/NC ratio). We determine standard model predictions for the CC spectral shape and for the CC/NC ratio, together with realistic estimates of their errors and the correlations between errors. We consider systematic uncertainties in the standard neutrino spectrum and in the charged-current and neutral current cross-sections, the SNO energy resolution and absolute energy scale, and the SNO detection efficiencies. Assuming that either matter-enhanced or vacuum neutrino oscillations solve the solar neutrino problems, we calculate the confidence levels with which electron flavor non-conservation can be detected using either the CC spectrum shape or the CC/NC ratio, or both. If the SNO detector works as expected, the neutrino oscillation solutions that best-fit the results of the four operating solar neutrino experiments can be distinguished unambiguously from the standard predictions of electron flavor conservation.

hep-ph↗

arXiv1996

Three-flavor atmospheric neutrino anomaly

We investigate the indications of flavor oscillations that come from the anomalous flavor composition of the atmospheric neutrino flux observed in some underground experiments. We study the information coming from the neutrino-induced $μ$-like and $e$-like events both in the sub-GeV energy range (Kamiokande, IMB, Fr{é}jus, and NUSEX experiments) and in the multi-GeV energy range (Kamiokande experiment). First we analyze all the data in the limits of pure $ν_μ\leftrightarrowν_τ$ and $ν_μ\leftrightarrowν_e$ oscillations. We obtain that $ν_μ\leftrightarrowν_e$ oscillations provide a better fit, in particular to the multi-GeV data. Then we perform a three-flavor analysis in the hypothesis of dominance of one neutrino square mass difference, $m^2$, implying that the neutrino mixing is parametrized by two angles, $(ψ,\,ϕ)\in[0,\,π/2]$. We explore the space $(m^2,\,ψ,\,ϕ)$ exhaustively, and find the regions favored by the oscillation hypothesis. The results are displayed in a form suited to the comparison with other flavor oscillation searches at accelerator, reactor, and solar $ν$ experiments. In the analysis, we pay particular attention to the earth matter effects, to the correlation of the uncertainties, and to the symmetry properties of the oscillation probability.

hep-ph↗

arXiv1996

Matter-enhanced Three-flavor Oscillations and the Solar Neutrino Problem

We present a systematic analysis of the three-flavor Mikheyev-Smirnov-Wolfenstein (MSW) oscillation solutions to the solar neutrino problem, in the hypothesis that the two independent neutrino square mass differences, $δm^2$ and $m^2$, are well separated: $δm^2 \ll m^2$. At zeroth order in $δm^2/m^2$, the relevant variables for solar neutrinos are $δm^2$ and two mixing angles, $ω$ and $ϕ$. We introduce new graphical representations of the parameter space $(δm^2,\,ω,\,ϕ)$, that prove useful both to analyze the properties of the electron-neutrino survival probability and to present the results of the analysis of solar neutrino data. We make a detailed comparison between the theoretical predictions of the Bahcall--Pinsonneault standard solar model and the current experimental results on solar neutrino rates, and discuss thoroughly the MSW solutions found by spanning the whole three-flavor space $(δm^2,\,ω,\,ϕ)$. The allowed regions can be radically different from the usual ``small mixing'' and ``large mixing'' solutions, characteristic of the usual two-generation MSW approach. We also discuss the link between these results and the independent information on neutrino masses and mixings coming from accelerator and reactor oscillation searches.

hep-ph↗

arXiv1996

Tests of three-flavor mixing in long-baseline neutrino oscillation experiments

We compare the effectiveness of various tests of three-flavor mixing in future long-baseline neutrino oscillation experiments. We analyze a representative case of mixing in a simplified three-flavor scheme, whose relevant parameters are one neutrino mass-square difference, $m^2$, and two mixing angles, $ψ$ and $ϕ$. We show that an unambiguous determination of $ψ$ and $ϕ$ requires flavor-appearance tests in accelerator experiments, as well as supplementary information from reactor experiments.

hep-ph↗