Indications on neutrino oscillations parameters from initial K2K and current SK data

We briefly discuss the impact of initial data from the KEK-to-Kamioka (K2K) neutrino experiment on the nu_mu-->nu_tau oscillation parameters (m^2,tan^2 psi) currently indicated by the Super-Kamiokande (SK) atmospheric neutrino experiment. After showing the very good agreement between K2K and SK, we combine the two separate pieces of information. We find that the 99% C.L. range for m^2 allowed by SK only, m^2=[1.3, 5.6]x10^-3 eV^2, is reduced to [1.5, 4.8]x10^-3 eV^2 by including K2K data. By halving the uncertainties of the K2K total rate (with central value unchanged), the m^2 range would be ulteriorly reduced to [1.8, 4.0]x10^-3 eV^2. Such information appears to be already useful in planning (very) long baseline neutrino oscillation experiments

Neutrino mass hierarchy and precision physics with medium-baseline reactors: impact of energy-scale and flux-shape uncertainties

Nuclear reactors provide intense sources of electron antineutrinos, characterized by few-MeV energy E and unoscillated spectral shape Phi(E). High-statistics observations of reactor neutrino oscillations over medium-baseline distances L ~ O(50) km would provide unprecedented opportunities to probe both the long-wavelength mass-mixing parameters (delta m^2 and theta_12) and the short-wavelength ones (Delta m^2 and theta_13), together with the subtle interference effects associated to the neutrino mass hierarchy (either normal or inverted). In a given experimental setting - here taken as in the JUNO project for definiteness - the achievable hierarchy sensitivity and parameter accuracy depend not only on the accumulated statistics but also on systematic uncertainties, which include (but are not limited to) the mass-mixing priors and the normalizations of signals and backgrounds. We examine, in addition, the effect of introducing smooth deformations of the detector energy scale, E -> E'(E), and of the reactor flux shape, Phi(E) -> Phi'(E), within reasonable error bands inspired by state-of-the-art estimates. It turns out that energy-scale and flux-shape systematics can noticeably affect the performance of a JUNO-like experiment, both on the hierarchy discrimination and on precision oscillation physics. It is shown that a significant reduction of the assumed energy-scale and flux-shape uncertainties (by, say, a factor of two) would be highly beneficial to the physics program of medium-baseline reactor projects. Our results shed also some light on the role of the inverse-beta decay threshold, of geoneutrino backgrounds, and of matter effects in the analysis of future reactor oscillation data

Neutrino mass hierarchy and electron neutrino oscillation parameters with one hundred thousand reactor events

Proposed medium-baseline reactor neutrino experiments offer unprecedented opportunities to probe, at the same time, the mass-mixing parameters which govern $\nu_e$ oscillations both at short wavelength (delta m^2 and theta_{12}) and at long wavelength (Delta m^2 and theta_{13}), as well as their tiny interference effects related to the mass hierarchy (i.e., the relative sign of Delta m^2 and delta m^2). In order to take full advantage of these opportunities, precision calculations and refined statistical analyses of event spectra are required. In such a context, we revisit several input ingredients, including: nucleon recoil in inverse beta decay and its impact on energy reconstruction and resolution, hierarchy and matter effects in the oscillation probability, spread of reactor distances, irreducible backgrounds from geoneutrinos and from far reactors, and degeneracies between energy scale and spectrum shape uncertainties. We also introduce a continuous parameter alpha, which interpolates smoothly between normal hierarchy (alpha=+1) and inverted hierarchy (alpha=-1). The determination of the hierarchy is then transformed from a test of hypothesis to a parameter estimation, with a sensitivity given by the distance of the true case (either alpha=+1 or alpha=-1) from the undecidable case (alpha=0). Numerical experiments are performed for the specific set up envisaged for the JUNO project, assuming a realistic sample of O(10^5) reactor events. We find a typical sensitivity of ~2 sigma to the hierarchy in JUNO, which, however, can be challenged by energy scale and spectrum shape systematics, whose possible conspiracy effects are investigated. The prospective accuracy reachable for the other mass-mixing parameters is also discussed

PINGU and the neutrino mass hierarchy: Statistical and systematic aspects

The proposed PINGU project (Precision IceCube Next Generation Upgrade) is expected to collect O(10^5) atmospheric muon and electron neutrino in a few years of exposure, and to probe the neutrino mass hierarchy through its imprint on the event spectra in energy and direction. In the presence of nonnegligible and partly unknown shape systematics, the analysis of high-statistics spectral variations will face subtle challenges that are largely unprecedented in neutrino physics. We discuss these issues both on general grounds and in the currently envisaged PINGU configuration, where we find that possible shape uncertainties at the (few) percent level can noticeably affect the sensitivity to the hierarchy. We also discuss the interplay between the mixing angle theta_23 and the PINGU sensitivity to the hierarchy. Our results suggest that more refined estimates of spectral uncertainties are needed in next-generation, large-volume atmospheric neutrino experiments

Solar Neutrinos (with a tribute to John. N. Bahcall)

John N. Bahcall championed solar neutrino physics for many years. Thanks to his pioneering and long-lasting contributions, this field of research has not only reached maturity, but has also opened a new window on physics beyond the standard electroweak model through the phenomenon of neutrino flavor oscillations. We briefly outline some recent accomplishments in the field, and also discuss a couple of issues that do not seem to fit in the ``standard picture,'' namely, the chemical controversy at the solar surface, and possible implications of recent gallium radioactive source experiments

Neutrino mass and mixing parameters: A short review

We present a brief review of the current status of neutrino mass and mixing parameters, based on a comprehensive phenomenological analysis of neutrino oscillation and non-oscillation searches, within the standard three-neutrino mixing framework

Neutrino Oscillations: A Global Analysis

We review the status of the neutrino oscillation physics (as of June 2003), with a particular emphasis on the present knowledge of the neutrino mass-mixing parameters in a three generation approach. We consider first the nu_mu-->nu_tau flavor transitions of atmospheric neutrinos. It is found that standard oscillations provide the best description of the SK+K2K data, and that the associated mass-mixing parameters are determined at 1 sigma (and dof=1) as: Delta m^2=(2.6 +-0.4) x 10^-3 eV^2 and sin^2(2theta)=1.00+0.00-0.05. Such indications, presently dominated by SK, could be strengthened by further K2K data. Then we analyze the energy spectrum of reactor neutrino events recently observed at KamLAND and combine them with solar and terrestrial neutrino data. We find that the solution to the solar neutrino problem at large mixing angle (LMA) is basically split into two sub-regions, that we denote as LMA-I and LMA-II. The LMA-I solution, characterized by lower values of the squared neutrino mass gap, is favored by the global data fit. Finally, we briefly illustrate how prospective data from the SNO and KamLAND can increase our confidence in the occurrence of standard matter effects in the Sun, which are starting to emerge from current data

Low-energy spectral features of supernova (anti)neutrinos in inverted hierarchy

In the dense supernova core, self-interactions may align the flavor polarization vectors of neutrinos and antineutrinos, and induce collective flavor transformations. Different alignment ansatzes are known to describe approximately the phenomena of synchronized or bipolar oscillations, and the split of neutrino energy spectra. We discuss another phenomenon observed in some numerical experiments in inverted hierarchy, showing features akin to a low-energy split of antineutrino spectra. The phenomenon appears to be approximately described by another alignment ansatz which, in the considered scenario, reduces the (nonadiabatic) dynamics of all energy modes to only two neutrino plus two antineutrino modes. The associated spectral features, however, appear to be fragile when passing from single- to multi-angle simulations