Indications of neutrino oscillation in a 250 km long-baseline experiment

Synergies and prospects for early resolution of the neutrino mass ordering

The measurement of neutrino mass ordering (MO) is a fundamental element for the understanding of leptonic flavour sector of the Standard Model of Particle Physics. Its determination relies on the precise measurement of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta m^2_{31}$$\end{document}Δm312 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta m^2_{32}$$\end{document}Δm322 using either neutrino vacuum oscillations, such as the ones studied by medium baseline reactor experiments, or matter effect modified oscillations such as those manifesting in long-baseline neutrino beams (LB\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu$$\end{document}νB) or atmospheric neutrino experiments. Despite existing MO indication today, a fully resolved MO measurement (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\ge 5\sigma$$\end{document}≥5σ) is most likely to await for the next generation of neutrino experiments: JUNO, whose stand-alone sensitivity is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 3\sigma$$\end{document}∼3σ, or LB\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu$$\end{document}νB experiments (DUNE and Hyper-Kamiokande). Upcoming atmospheric neutrino experiments are also expected to provide precious information. In this work, we study the possible context for the earliest full MO resolution. A firm resolution is possible even before 2028, exploiting mainly vacuum oscillation, upon the combination of JUNO and the current generation of LB\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu$$\end{document}νB experiments (NOvA and T2K). This opportunity is possible thanks to a powerful synergy boosting the overall sensitivity where the sub-percent precision of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta m^2_{32}$$\end{document}Δm322 by LB\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu$$\end{document}νB experiments is found to be the leading order term for the MO earliest discovery. We also found that the comparison between matter and vacuum driven oscillation results enables unique discovery potential for physics beyond the Standard Model.

Neutrino Dynamics in a Quantum-Corrected Schwarzschild Spacetime

We study neutrino propagation in a curved spacetime background described by the Schwarzschild solution with the addition of quantum corrections evaluated in the framework of perturbative quantum gravity at lowest order. In particular, we investigate neutrino oscillations and decoherence within the Gaussian wave packet description, finding that quantum gravity corrections significantly affect the intrinsic features of mixed particles and induce potentially measurable physical effects.

Prospects for the Detection of the Diffuse Supernova Neutrino Background with the Experiments SK-Gd and JUNO

The advent of gadolinium-loaded Super-Kamiokande (SK-Gd) and of the soon-to-start JUNO liquid scintillator detector marks a substantial improvement in global sensitivity for the Diffuse Supernova Neutrino Background (DSNB). The present article reviews the detector properties most relevant for the DSNB searches in both experiments and estimates the expected signal and background levels. Based on these inputs, we evaluate the sensitivity of both experiments individually and combined. Using a simplified statistical approach, we find that both SK-Gd and JUNO have the potential to reach >3σ evidence of the DSNB signal within 10 years of measurement. Combination of their results is likely to enable a 5σ discovery of the DSNB signal within the next decade.

Imprint of the Seesaw Mechanism on Feebly Interacting Dark Matter and the Baryon Asymmetry

We show that the type-I seesaw, responsible for generating the light neutrino mass, itself is capable of accommodating one of the three right handed neutrinos as a freeze-in type of dark matter where the required smallness of the associated coupling is connected to the lightness of the (smallest) active neutrino mass. It turns out that (a) the nonthermal production of dark matter having mass ≲O(1)  MeV (via decays of W, Z bosons and standard model Higgs) consistent with relic density and (b) its stability determine this smallest active neutrino mass uniquely ∼O(10^{-12})  eV. On the other hand, the study of flavor leptogenesis in this scenario (taking into account the latest neutrino data and Higgs vacuum stability issue) fixes the scale of two other right handed neutrinos.

Astrophysical Neutrinos in Testing Lorentz Symmetry

An overview of searches related to neutrinos of astronomical and astrophysical origin performed within the framework of the Standard-Model Extension is provided. For this effective field theory, key definitions, intriguing physical consequences, and the mathematical formalism are summarized within the neutrino sector to search for effects from a background that could lead to small deviations from Lorentz symmetry. After an introduction to the fundamental theory, examples of various experiments within the astronomical and astrophysical context are provided. Order-of-magnitude bounds of SME coefficients are shown illustratively for the tight constraints that this sector allows us to place on such violations.

What Is Matter According to Particle Physics, and Why Try to Observe Its Creation in a Lab?

The standard model of elementary interactions has long qualified as a theory of matter, in which the postulated conservation laws (one baryonic and three leptonic) acquire theoretical meaning. However, recent observations of lepton number violations—neutrino oscillations—demonstrate its incompleteness. We discuss why these considerations suggest the correctness of Ettore Majorana’s ideas on the nature of neutrino mass and add further interest to the search for an ultra-rare nuclear process in which two particles of matter (electrons) are created, commonly called neutrinoless double beta decay. The approach of the discussion is mainly historical, and its character is introductory. Some technical considerations, which highlight the usefulness of Majorana’s representation of gamma matrices, are presented in the appendix.

General Quantum Field Theory of Flavor Mixing and Oscillations

We review the canonical transformation in quantum physics known as the Bogoliubov transformation and present its application to the general theory of quantum field mixing and oscillations with an arbitrary number of mixed particles with either boson or fermion statistics. The mixing relations for quantum states are derived directly from the definition of mixing for quantum fields and the unitary inequivalence of the Fock space of energy and flavor eigenstates is shown by a straightforward algebraic method. The time dynamics of the interacting fields is then explicitly solved and the flavor oscillation formulas are derived in a unified general formulation with emphasis on antiparticle content and effect introduced by nontrivial flavor vacuum.

Rephasing Invariant for Three-Neutrino Oscillations Governed by a Non-Hermitian Hamiltonian

Time-reversal symmetry is broken for mixed and possibly unstable Dirac neutrino propagation through absorbing media. This implies that interplay between the neutrino mixing, refraction, absorption and/or decay can be described by non-Hermitian quantum dynamics. We derive an identity which sets up direct connection between the fundamental neutrino parameters (mixing angles, CP-violating phase, mass-squared splittings) in vacuum and their effective counterparts in matter.

Three-Flavor Oscillations with Accelerator Neutrino Beams

The three-flavor neutrino oscillation paradigm is well established in particle physics thanks to the crucial contribution of accelerator neutrino beam experiments. In this paper, we review the most important contributions of these experiments to the physics of massive neutrinos after the discovery of θ 13 and future perspectives in such a lively field of research. Special emphasis is given to the technical challenges of high power beams and the oscillation results of T2K, OPERA, ICARUS, and NO ν A. We discuss in detail the role of accelerator neutrino experiments in the precision era of neutrino physics in view of DUNE and Hyper-Kamiokande, the program of systematic uncertainty reduction and the development of new beam facilities.

The Sterile Neutrino: A short introduction

This is a pedagogical introduction to the main concepts of the sterile neutrino - a hypothetical particle, coined to resolve some anomalies in neutrino data and retain consistency with observed widths of the W and Z bosons. We briefly review existing anomalies and the oscillation parameters that best describe these data. We discuss in more detail how sterile neutrinos can be observed, as well as the consequences of its possible existence. In particular, we pay attention to a possible loss of coherence in a model of neutrino oscillations with sterile neutrinos, where this effect might be of a major importance with respect to the 3ν model. The current status of searches for a sterile neutrino state is also briefly reviewed.

A review of μ-τ flavor symmetry in neutrino physics

Behind the observed pattern of lepton flavor mixing is a partial or approximate μ-τ flavor symmetry-a milestone on our road to the true origin of neutrino masses and flavor structures. In this review article we first describe the features of μ-τ permutation and reflection symmetries, and then explore their various consequences on model building and neutrino phenomenology. We pay particular attention to soft μ-τ symmetry breaking, which is crucial for our deeper understanding of the fine effects of flavor mixing and CP violation.

Physics at the [Formula: see text] linear collider

A comprehensive review of physics at an [Formula: see text] linear collider in the energy range of [Formula: see text] GeV-3 TeV is presented in view of recent and expected LHC results, experiments from low-energy as well as astroparticle physics. The report focusses in particular on Higgs-boson, top-quark and electroweak precision physics, but also discusses several models of beyond the standard model physics such as supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analysed as well.

Searches for Lepton flavor violation in the decays tau{+/-}-->e{+/-}gamma and tau{+/-}-->mu{+/-}gamma

Searches for lepton-flavor-violating decays of a tau lepton to a lighter mass lepton and a photon have been performed with the entire data set of (963+/-7)x10{6} tau decays collected by the BABAR detector near the Upsilon(4S), Upsilon(3S) and Upsilon(2S) resonances. The searches yield no evidence of signals and we set upper limits on the branching fractions of B(tau{+/-}-->e{+/-}gamma)<3.3x10{-8} and B(tau{+/-}-->mu{+/-}gamma)<4.4x10{-8} at 90% confidence level.

Search for lepton flavor violating decays tau+/--->l+/-omega

A search for lepton flavor violating decays of a tau to a lighter-mass charged lepton and an omega vector meson is performed using 384.1 fb(-1) of e(+)e(-) annihilation data collected with the BABAR detector at the Stanford Linear Accelerator Center PEP-II storage ring. No signal is found, and the upper limits on the branching ratios are determined to be B(tau(+/-)-->e;{+/-}omega)<1.1 x10 (-7) and B(tau(+/-)-->micro(+/-)omega)<1.0 x 10(-7) at 90% confidence level.

Superscaling predictions for neutral current quasielastic neutrino-nucleus scattering

The application of superscaling ideas to predict neutral-current (NC) quasielastic (QE) neutrino cross sections is investigated. The relativistic impulse approximation (RIA) using the same relativistic mean field potential (RMF) for both initial and final nucleons - a model that reproduces the experimental (e,e(')) scaling function - is used to illustrate our findings. While NC reactions are apparently not well suited for scaling analyses, to a large extent, the RIA-RMF predictions do exhibit superscaling. Independence of the scaled response on the nuclear species is very well fulfilled. The RIA-RMF NC superscaling function is in good agreement with the experimental (e,e(')) one. The idea that electroweak processes can be described with a universal scaling function, provided that mild restrictions on the kinematics are assumed, is shown to be valid.

Improved limits on the lepton-flavor violating decays tau{-}-->l{-}l{+}l{-}

A search for the neutrinoless, lepton-flavor violating decay of the tau lepton into three charged leptons has been performed using 376 fb{-1} of data collected at an e{+}e{-} center-of-mass energy around 10.58 GeV with the BABAR detector at the SLAC PEP-II storage rings. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (4-8)x10{-8} at 90% confidence level.

Testing the standard model by precision measurement of the weak charges of quarks

In a global analysis of the latest parity-violating electron scattering measurements on nuclear targets, we demonstrate a significant improvement in the experimental knowledge of the weak neutral-current lepton-quark interactions at low energy. The precision of this new result, combined with earlier atomic parity-violation measurements, places tight constraints on the size of possible contributions from physics beyond the standard model. Consequently, this result improves the lower-bound on the scale of relevant new physics to approximately 1 TeV.

Search for electron neutrino appearance at the Delta m2 approximately 1 eV2 scale

The MiniBooNE Collaboration reports first results of a search for nu e appearance in a nu mu beam. With two largely independent analyses, we observe no significant excess of events above the background for reconstructed neutrino energies above 475 MeV. The data are consistent with no oscillations within a two-neutrino appearance-only oscillation model.

Search for lepton flavor violating decays tau(+/-) --> l(+/-)pi0, l(+/-)eta, l(+/-)eta'

A search for lepton flavor violating decays of the tau lepton to a lighter mass lepton and a pseudoscalar meson has been performed using 339 fb;{-1} of e;{+}e;{-} annihilation data collected at a center-of-mass energy near 10.58 GeV by the BABAR detector at the SLAC PEP-II storage ring. No evidence of a signal has been found, and upper limits on the branching fractions are set at the 10;{-7} level.