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 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, 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 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 inverse-beta decay threshold, of geoneutrino backgrounds, and of matter effects in the analysis of future reactor oscillation data.Comment: 13 pages, including 17 figures. Minor changes in the text, references added. To appear in Phys. Rev.

Four-neutrino oscillation solutions of the atmospheric neutrino anomaly

In the context of neutrino scenarios characterized by four (three active plus one sterile) neutrino species and by mass spectra with two separated doublets, we analyze solutions to the atmospheric neutrino anomaly which smoothly interpolate between \nu_\mu-->\nu_\tau and \nu_\mu-->\nu_s oscillations. We show that, although the Super-Kamiokande data disfavor the pure \nu_\mu-->\nu_s channel, they do not exclude its occurrence, with sizable amplitude, in addition to the \nu_\mu-->\nu_\tau channel. High energy muon data appear to be crucial in assessing the relative amplitude of active and sterile neutrino oscillations. It is also qualitatively shown that such atmospheric \nu solutions are compatible with analogous solutions to the solar neutrino problem, which involve oscillations of \nu_e in both sterile and active states.Comment: Added references. Accepted for publication in Phys. Rev.

Global analysis of three-flavor neutrino masses and mixings

We present a comprehensive phenomenological analysis of a vast amount of data from neutrino flavor oscillation and non-oscillation searches, performed within the standard scenario with three massive and mixed neutrinos, and with particular attention to subleading effects. The detailed results discussed in this review represent a state-of-the-art, accurate and up-to-date (as of August 2005) estimate of the three-neutrino mass-mixing parameters.Comment: Final version (including a new Appendix), to be published in "Progress in Particle and Nuclear Physics". Higher-resolution pdf file and eps figures can be download from http://www.ba.infn.it/~now2004/PPNP_review

Supernova neutrinos: Strong coupling effects of weak interactions

In core-collapse supernovae, neutrinos and antineutrinos are initially subject to significant self-interactions induced by weak neutral currents, which may induce strong-coupling effects on the flavor evolution (collective transitions). The interpretation of the effects is simplified when self-induced collective transitions are decoupled from ordinary matter oscillations, as for the matter density profile that we discuss. In this case, approximate analytical tools can be used (pendulum analogy, swap of energy spectra). For inverted neutrino mass hierarchy, the sequence of effects involves: synchronization, bipolar oscillations, and spectral split. Our simulations shows that the main features of these regimes are not altered when passing from simplified (angle-averaged) treatments to full, multi-angle numerical experiments.Comment: Proceedings of NO-VE 2008, IV International Workshop on "Neutrino Oscillations in Venice" (Venice, Italy, April 15-18, 2008), edited by M. Baldo Ceolin (University of Padova publication, Papergraf Editions, Padova, Italy, 2008), pages 233-24

Neutrino masses and mixings: Status of known and unknown 3ν3\nu parameters

Within the standard 3nu mass-mixing framework, we present an up-to-date global analysis of neutrino oscillation data (as of January 2016), including the latest available results from experiments with atmospheric neutrinos (Super-Kamiokande and IceCube DeepCore), at accelerators (first T2K anti-nu and NOvA nu runs in both appearance and disappearance mode), and at short-baseline reactors (Daya Bay and RENO far/near spectral ratios), as well as a reanalysis of older KamLAND data in the light of the "bump" feature recently observed in reactor spectra. We discuss improved constraints on the five known oscillation parameters (delta m^2, |Delta m^2|, sin^2theta_12, sin^2theta_13, sin^2theta_23), and the status of the three remaining unknown parameters: the mass hierarchy, the theta_23 octant, and the possible CP-violating phase delta. With respect to previous global fits, we find that the reanalysis of KamLAND data induces a slight decrease of both delta m^2 and sin^2theta_12, while the latest accelerator and atmospheric data induce a slight increase of |Delta m^2|. Concerning the unknown parameters, we confirm the previous intriguing preference for negative values of sin(delta) [with best-fit values around sin(delta) ~ -0.9], but we find no statistically significant indication about the theta_23 octant or the mass hierarchy (normal or inverted). Assuming an alternative (so-called LEM) analysis of NOvA data, some delta ranges can be excluded at >3 sigma, and the normal mass hierarchy appears to be slightly favored at 90% C.L. We also describe in detail the covariances of selected pairs of oscillation parameters. Finally, we briefly discuss the implications of the above results on the three non-oscillation observables sensitive to the (unknown) absolute nu mass scale: the sum of nu masses, the effective nu_e mass, and the effective Majorana mass.Comment: 15 pages, 9 figures, 2 tables. Invited contribution prepared for the Nuclear Physics B Special Issue on "Neutrino Oscillations" celebrating the Nobel Prize in Physics 201

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.Comment: 11 pages, including 7 figures. Presented at the 40th Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Aosta Valley, Italy, 5-12 Mar 200

Zenith distribution of atmospheric neutrino events and electron neutrino mixing

Assuming atmospheric neutrino oscillations with dominant nu_munu_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_munu_tau transitions) do not vanish in the limit of energy-averaged oscillations.Comment: 6 pages, RevTeX, no figure

Atmospheric, Solar, and CHOOZ neutrinos: a global three generation analysis

We perform a global three generation analysis of the current solar and atmospheric evidence in favor of neutrino oscillations. We also include the negative results coming from CHOOZ to constrain the nu_e mixing. We study the zones of mass-mixing oscillations parameters compatible with all the data. It is shown that almost pure nu_mu nu_tau oscillations are required to explain the atmospheric neutrino anomaly and almost pure nu_1 nu_2 oscillations to account for the solar neutrino deficit.Comment: 4 pages, talk given at 36th Rencontres de Moriond: Electroweak Interactions and Unified Theories, Les Arcs, France, 10-17 Mar 200