arXiv subjects

D. Montanino

Publications and source records attributed to D. Montanino.

48 records · Page 3Linked to original sources

arXiv1999

Testing solar neutrino MSW oscillations at low delta m^2 through time variations of event rates in GNO and BOREXINO

The Mikheyev-Smirnov-Wolfenstein (MSW) explanation of the solar neutrino problem is currently compatible with three distinct regions of the two-neutrino oscillation parameter space (delta m^2,sin^2 2theta). We focus on the region with the lowest value of delta m^2 (~10^{-7} eV^2), which implies significant Earth regeneration effects for low-energy solar neutrinos. We point out that such effects are not only observable as day-night variations of neutrino event rates in the real-time BOREXINO experiment, but also as seasonal variations in the radiochemical Gallium Neutrino Observatory (GNO) at Gran Sasso. We present detailed calculations of the difference between winter and summer rates in GNO (six months averages) in excess of the trivial seasonal variation due to the Earth orbital eccentricity. We show that, within the low-delta m^2 MSW solution, the net winter-summer GNO rate difference amounts to 4-6 SNU, with a dominant contribution from pp neutrinos. We also give analytical expressions for the winter and summer solar exposure functions at the Gran Sasso site.

hep-ph↗

arXiv1999

Can unstable relics save pure Cold Dark Matter?

The standard CDM model fails to describe the power spectrum of fluctuations since it gives too much power at small scales. Among other possible improvements, it has been suggested that an agreement with observations can be achieved with the addition of a late decaying particle, through the injection of non-thermal radiation and the consequent increase of the horizon length at the equivalence time. We analyze the possibility of implementing this idea in some extensions of the electroweak standard model, discussing the cosmological and astrophysical bounds to which these schemes are subject.

hep-ph↗

arXiv1999

Test of non-standard neutrino properties with the BOREXINO source experiments

We calculate the event rates induced by high-intensity radioactive sources of nu_e (51Cr) and of anti-nu_e (90Sr), to be located near the BOREXINO detector. Calculations are performed both in the standard case and assuming non-standard properties of neutrinos, including flavor oscillations, neutrino electromagnetic interactions, and deviations from the standard vector and axial couplings in the nu_e-e interaction. It is shown that, in some cases, the current limits on non-standard neutrino properties can be significantly improved.

hep-ex↗

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

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↗

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

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↗