Search results for " Neutrino"
showing 10 items of 727 documents
Are solar neutrino oscillations robust?
2004
The robustness of the large mixing angle (LMA) oscillation (OSC) interpretation of the solar neutrino data is considered in a more general framework where non-standard neutrino interactions (NSI) are present. Such interactions may be regarded as a generic feature of models of neutrino mass. The 766.3 ton-yr data sample of the KamLAND collaboration are included in the analysis, paying attention to the background from the reaction ^13C(\alpha,n) ^16O. Similarly, the latest solar neutrino fluxes from the SNO collaboration are included. In addition to the solution which holds in the absence of NSI (LMA-I) there is a 'dark-side' solution (LMA-D) with sin^2 theta_Sol = 0.70, essentially degenerat…
The simplest resonant spin-flavour solution to the solar neutrino problem
2000
We re-analyse the resonant spin-flavour (RSF) solutions to the solar neutrino problem in the framework of analytic solutions to the solar magneto-hydrodynamics (MHD) equations. By substantially eliminating the arbitrariness associated to the magnetic field profile due to both mathematical consistency and physical requirements we propose the simplest scheme (MHD-RSF, for short) for solar neutrino conversion using realistic static MHD solutions. Using such effective two-parameter scheme we perform the first global fit of the recent solar neutrino data, including event rates as well as zenith angle distributions and recoil electron spectra induced by solar neutrino interactions in Superkamioka…
Confronting spin flavor solutions of the solar neutrino problem with current and future solar neutrino data
2002
We show that spin flavor precession solutions to the solar neutrino problem, although preferred by the latest solar data, are ruled out by the first results from the KamLAND reactor experiment, at more than 3_sigma. An illustrative chi2 plot comparing these descriptions with oscillations is given.
Solar neutrino problem accounting for self-consistent magnetohydrodynamics solution for solar magnetic fields
2001
The analysis of the resonant spin-flavour (RSF) solutions to the solar neutrino problem in the framework of simplest analytic solutions to the solar magneto-hydrodynamics (MHD) equations is presented. We performed the global fit of the recent solar neutrino data, including event rates as well as day and night recoil electron spectra induced by solar neutrino interactions in SuperKamiokande. We compare quantitatively our simplest MHD-RSF fit with vacuum oscillation (VAC) and MSW--type (SMA, LMA and LOW) solutions to the solar neutrino problem using a common well-calibrated theoretical calculation and fit procedure and find MHD-RSF fit to be somewhat better than those obtained for the favored…
Constraining Majorana neutrino electromagnetic properties from the LMA-MSW solution of the solar neutrino problem
2002
In this paper we use solar neutrino data to derive stringent bounds on Majorana neutrino transition moments (TMs). Should such be present, they would contribute to the neutrino--electron scattering cross section and hence alter the signal observed in Super-Kamiokande. Motivated by the growing robustness of the LMA-MSW solution of the solar neutrino problem indicated by recent data, and also by the prospects of its possible confirmation at KamLAND, we assume the validity of this solution, and we constrain neutrino TMs by using the latest global solar neutrino data. We find that all elements of the TM matrix can be bounded at the same time. Furthermore, we show how reactor data play a complem…
Relic Neutrino Decoupling Including Flavour Oscillations
2005
In the early universe, neutrinos are slightly coupled when electron-positron pairs annihilate transferring their entropy to photons. This process originates non-thermal distortions on the neutrino spectra which depend on neutrino flavour, larger for nu_e than for nu_mu or nu_tau. We study the effect of three-neutrino flavour oscillations on the process of neutrino decoupling by solving the momentum-dependent kinetic equations for the neutrino spectra. We find that oscillations do not essentially modify the total change in the neutrino energy density, giving N_eff=3.046 in terms of the effective number of neutrinos, while the small effect over the production of primordial 4He is increased by…
Single-photon Z decays and small neutrino masses
1996
We discuss some rare Z decay signatures associated with extensions of the Standard Model with spontaneous lepton number violation at the electroweak scale. We show that single-photon Z decays such as $Z \to \gamma H$ and $Z \to \gamma J J$ where H is a CP-even Higgs boson and J denotes the associated CP-odd Majoron may occur with branching ratios accessible to LEP sensitivities, even though the corresponding neutrino masses can be very small, as required in order to explain the deficit of solar neutrinos.
Neutrinos and physics beyond the standard model
1997
A brief sketch is made of the present observational status of neutrino physics, with emphasis on the hints that follow from solar and atmospheric neutrino observations, as well as cosmological data on the amplitude of primordial density fluctuations. I also briefly review the ways to account for the observed anomalies and some of their implications.
Michel Parameters and tau neutrino Helicity From Decay Correlations In Z->tau+tau-
1995
The Michel parameters and the average tau-neutrino helicity are measured using correlations between the decays of the tau(+) and tau(-) produced on the Z resonance and observed in the ALEPH detector at LEP. The Michel parameters, rho(e), eta(e), xi(e), (delta xi)(e), are determined from tau --> e ($) over bar upsilon(e) upsilon(tau) with e = (e, mu), and the average tau neutrino helicity, (h(upsilon(tau))), from tau --> h tau with h = (pi, rho, a(1)). The results obtained with e-mu universality are: rho(e) = 0.751 +/- 0.039 +/- 0.022, eta(e) = -0.04 +/- 0.15 +/- 0.11, xi(e) = 1.18 +/- 0.15 +/- 0.06, (delta xi)(e) = 0.88 +/- 0.11 +/- 0.07, and the average tau neutrino helicity (h(upsilon(tau…
Light vector mediators facing XENON1T data
2020
Recently the XENON1T collaboration has released new results on searches for new physics in low-energy electronic recoils. The data shows an excess over background in the low-energy tail, particularly pronounced at about $2-3$ keV. With an exposure of $0.65$ tonne-year, large detection efficiency and energy resolution, the detector is sensitive as well to solar neutrino backgrounds, with the most prominent contribution given by $pp$ neutrinos. We investigate whether such signal can be explained in terms of new neutrino interactions with leptons mediated by a light vector particle. We find that the excess is consistent with this interpretation for vector masses below $\lesssim 0.1$ MeV. The r…