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Nuclear reactors provide intense sources of electron antineutrinos, characterized by few-MeV energy E and unoscillated spectral shape Φ(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 (δm2 and θ12) and the short-wavelength ones (Δm2ee and θ13), together with the subtle interference effects associated with 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, Φ(E) → Φ'(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 2) would be highly beneficial to the physics program of medium-baseline reactor projects. Our results also shed some light on the role of the inversebeta decay threshold, of geoneutrino backgrounds, and of matter effects in the analysis of future reactor oscillation data. [ABSTRACT FROM AUTHOR]

Theoretical estimates for the half-life of neutrinoless double beta decay (Ovββ) in candidate nuclei are affected by both particle and nuclear physics uncertainties, which may complicate the interpretation of decay signals or limits. We study such uncertainties and their degeneracies in the following context: three Ovββ nuclei of great interest for large-scale experiments (76Ge, 130Te, 136Xe), two representative particle physics mechanisms (light and heavy Majorana neutrino exchange), and a large set of nuclear matrix elements (NME), computed within the quasiparticle random phase approximation (QRPA). It turns out that the main theoretical uncertainties, associated with the effective axial coupling gA and with the nucleonnucleon potential, can be parametrized in terms of NME rescaling factors, up to small residuals. From this parametrization, the following QRPA features emerge: (1) the NME dependence on gA is milder than quadratic, (2) in each of the two mechanisms, the relevant lepton number violating parameter is largely degenerate with the NME rescaling factors, and (3) the light and heavy neutrino exchange mechanisms are basically degenerate in the above three nuclei. We comment on the challenging theoretical and experimental improvements required to reduce such particle and nuclear physics uncertainties and their degeneracies. [ABSTRACT FROM AUTHOR]

The proposed PINGU project (Precision IceCube Next Generation Upgrade) is expected to collect O(105) atmospheric muon and electron neutrino events 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 non-negligible 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 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. [ABSTRACT FROM AUTHOR]

Proposed medium-baseline reactor neutrino experiments offer unprecedented opportunities to probe, at the same time, the mass-mixing parameters which govern ve oscillations both at long wavelength (δm² and θ12) and at short wavelength (∆m² and θ13), as well as their tiny interference effects related to the mass hierarchy (i.e., the relative sign of ∆m² and δm²). 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 ɑ, which interpolates smoothly between normal hierarchy (ɑ = +1) and inverted hierarchy (ɑ = -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 ɑ=+1 or ɑ=-1) from the "undecidable" case (ɑ=0). Numerical experiments are performed for the specific setup envisaged for the JUNO project, assuming a realistic sample of O(105) reactor events. We find a typical sensitivity of ~2ɑ 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. [ABSTRACT FROM AUTHOR]

We perform a global analysis of neutrino oscillation data, including high-precision measurements of the neutrino mixing angle &thetas;13 at reactor experiments, which have confirmed previous indications in favor of &thetas;13 > 0. Recent data presented at the Neutrino 2012 conference are also included. We focus on the correlations between &thetas;13 and the mixing angle &thetas;23, as well as between &thetas;13 and the neutrino CP-violation phase &dgr;. We find interesting indications for &thetas;23 < &pgr;/4 and possible hints for &dgr; ∼ IT, with no significant difference between normal and inverted mass hierarchy. [ABSTRACT FROM AUTHOR]

The neutrino mixing angle θ13 is at the focus of current neutrino research. From a global analysis of the available oscillation data in a 3v framework, we previously reported [Phys. Rev. Lett. 101, 141801 (2008)] hints in favor of θ13 > 0 at the 90% C.L. Such hints are consistent with the recent indications of a vμ → ve appearance in the T2K and MINOS long-baseline accelerator experiments. Our global analysis of all the available data currently provides >3σ evidence for nonzero θ13, with 1σ ranges sin²θ13 = 0.021 ± 0.007 or 0.025 ± 0.007, depending on reactor neutrino flux systematics. Updated ranges are also reported for the other 3v oscillation parameters (δm², sin²θ12) and (Δm², sin²θ23). [ABSTRACT FROM AUTHOR]

In a previous article [A. Faessler et al., Phys. Rev. D 79, 053001 (2009)], we estimated the correlated uncertainties associated to the nuclear matrix elements of neutrinoless double beta decay (Ovββ) within the quasiparticle random phase approximation. Such estimates encompass recent independent calculations of nuclear matrix elements and can thus still provide a fair representation of the nuclear model uncertainties. In this context, we compare the claim of Ovββ decay in 76Ge with recent negative results in 136Xe and in other nuclei, and we infer the lifetime ranges allowed or excluded at 90% C.L. We also highlight some issues that should be addressed in order to properly compare and combine results coming from different Ovββ candidate nuclei. [ABSTRACT FROM AUTHOR]

The KamLAND and Borexino experiments have observed, each at ˜4σ level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. To this purpose, we analyze in detail the experimental Th and U geoneutrino event rates in KamLAND and Borexino, including neutrino oscillation effects. We estimate the crustal flux at the two detector sites, using state-of-the-art information about the Th and U distribution on global and local scales. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ~2.4σ level by combining the KamLAND and Borexino data. The inferred mantle flux slightly favors scenarios with relatively high Th and U abundances, within ±1σuncertainties comparable to the spread of predictions from recent mantle models. [ABSTRACT FROM AUTHOR]

We calculate nuclear matrix elements of neutrinoless double beta decay (0vββ) in four different candidate nuclei (76Ge, 82Se, 100Mo, 130Te) within the quasiparticle random phase approximation and its uncertainties. We assume (up to) four coexisting mechanisms for 0v2β decay, mediated by light Majorana neutrino exchange (z), heavy Majorana neutrino exchange (N), R-parity breaking supersymmetry (R), and squark-neutrino (q~) interfering either constructively or destructively with each other. We find that, unfortunately, current nuclear matrix element uncertainties appear to prevent a robust determination of the relative contribution of each mechanism to the decay amplitude, even assuming accurate measurements of decay lifetimes. The near-degeneracy of 0vββ mechanisms is analyzed with simple algebraic techniques, which do not involve assumptions about the statistical distribution of errors. We discuss implications of such degeneracy on prospective searches for absolute neutrino masses. [ABSTRACT FROM AUTHOR]