Search Results (17)

This paper presents a combined analysis of muon neutrino and antineutrino charged-current cross sections at kinematics of relevance for the T2K, MINERvA and MicroBooNE experiments. We analyze the sum, difference and asymmetry of neutrino versus antineutrino cross sections in order to get a better understanding of the nuclear effects involved in these processes. Nuclear models based on the superscaling behavior and the relativistic mean field theory are applied, covering a wide range of kinematics, from hundreds of MeV to several GeV, and the relevant nuclear regimes, i.e., from quasileastic reactions to deep inelastic scattering processes. The NEUT neutrino-interaction event generator, used in neutrino oscillation experiments, is also applied to the analysis of the quasielastic channel via local Fermi gas and spectral function approaches. Full article

At least two relics of the Big Bang have survived: the cosmological microwave background (CMB) and the cosmological neutrino background (C$\nu$B). Being the second most abundant particle in the universe, the neutrino has a significant impact on its evolution from the Big Bang to the present day. Neutrinos affect the following cosmological processes: the expansion rate of the universe, its chemical and isotopic composition, the CMB anisotropy and the formation of the large-scale structure of the universe. Another relic neutrino background is theoretically predicted, it consists of non-equilibrium antineutrinos of Primordial Nucleosynthesis arising as a result of the decay of neutrons and tritium nuclei. Such antineutrinos are an indicator of the baryon asymmetry of the universe. In addition to experimentally detectable active neutrinos, the existence of sterile neutrinos is theoretically predicted to generate neutrino masses and explain their oscillations. Sterile neutrinos can also solve such cosmological problems as the baryonic asymmetry of the universe and the nature of dark matter. The recent results of several independent experiments point to the possibility of the existence of a light sterile neutrino. However, the existence of such a neutrino is inconsistent with the predictions of the Standard Cosmological Model. The inclusion of a non-zero lepton asymmetry of the universe and/or increasing the energy density of active neutrinos can eliminate these contradictions and reconcile the possible existence of sterile neutrinos with Primordial Nucleosynthesis, the CMB anisotropy, and also reduce the H₀-tension. In this brief review, we discuss the influence of the physical properties of active and sterile neutrinos on the evolution of the universe from the Big Bang to the present day. Full article

T2K (Tokai to Kamioka) is a long baseline neutrino experiment that exploits a neutrino and antineutrino beam produced at the Japan Particle Accelerator Research Centre (J-PARC) to provide world-leading measurements of the parameters governing neutrino oscillation. Neutrino oscillations are analyzed by tuning the neutrino rates and spectra at a near detector complex, located at J-PARC, and extrapolating them to the water Cherenkov far detector, Super-Kamiokande, located 295 km away, where oscillations are observed. The latest T2K results include multiple analysis improvements, in particular, a new sample is added for the far detector analysis, requiring the presence of a pion in muon-neutrino interactions. This is the first time that a pion sample has been included in the study of neutrino disappearance at T2K and the first time a sample with more than one Cherenkov ring has been included in the T2K oscillation analysis, opening a road for further samples with charged and neutral pion tagging. The inclusion of such a sample enables proper control of the oscillated spectrum in a larger neutrino energy range and on subleading neutrino interaction processes. Finally, T2K is engaged with the Super-Kamiokande collaboration to combine T2K neutrino beam data and Super-Kamiokande atmospheric data to perform a joint fit of the oscillation parameters. Such a combination allows the degeneracies between the measurement of the CP-violating phase ${\delta }_{\mathrm{CP}}$ and the measurement of the ordering of the neutrino mass eigenstates to be lifted. A precise evaluation of the enhanced sensitivity of this joint fit will be presented. Full article

The Jiangmen Underground Neutrino Observatory (JUNO) is a neutrino experiment under construction in an underground laboratory with a 650 m rock overburden near Jiangmen in southern China. The detector’s main component will be 20 kton of liquid scintillator held in a spherical acrylic vessel. The experiment is designed for the determination of neutrino mass ordering, one of the key open questions in neutrino physics. This measurement will be based on observations of the vacuum oscillation pattern of antineutrinos from two nuclear power plants at a baseline of 53 km. The estimated sensitivity is 3$\sigma$ in about six years with 26.6 GW${}_{\mathrm{th}}$ of reactor power. A key ingredient for the success is an excellent and extremely challenging energy resolution of 3% at 1 MeV. The light produced by the scintillator will be seen by 17,612 large twenty-inch PMTs and 25,600 small three-inch PMTs. The OSIRIS detector will monitor the radio purity of the liquid scintillator during the months-long filling process of the main detector. The unoscillated antineutrino spectrum from one reactor core will be measured with unprecedented precision by the Taishan Antineutrino Observatory (TAO), located at a baseline of about 30 m. JUNO is expected to substantially improve the precision of ${sin}^{2}2{\theta }_{12}$, $\Delta m_{21}^2$, and $\Delta m_{31}^2$ neutrino oscillation parameters. Astrophysical measurements of solar, geo-, supernova, DSNB, and atmospheric neutrinos, as well as searching for proton decay and dark matter, are integral parts of the vast JUNO physics program. This contribution reviews the physics goals and current status of the JUNO project. Full article

A detailed understanding of neutrino–nucleus interactions is essential for the precise measurement of neutrino oscillations at long baseline experiments, such as T2K. The T2K near detector complex, designed to constrain the T2K flux and cross-section models, also provides a complementary program of neutrino interaction cross-section measurements. Through the use of multiple target materials (carbon, water, lead, iron), and the ability to sample different neutrino spectra (with detectors located on- and off-axis with respect to the beam direction), T2K is able to investigate atomic number and energy dependence of interaction cross-sections in a single experiment. In particular, T2K has recently performed the first joint on-/off-axis measurement of the charged current channel without pion in the final state. Furthermore, dedicated efforts are devoted to investigating rare or poorly studied interaction channels. Indeed, an improved analysis of the coherent pion production cross-section was recently accomplished, including an anti-neutrino sample for the first time. Those results, together with an overview of the T2K measurement strategy, adopted to reduce the model dependence, will be presented in these proceedings. Full article

We analyze neutrino emission channels in energetic ($\gtrsim {10}^{52}$ erg) long gamma-ray bursts within the binary-driven hypernova model. The binary-driven hypernova progenitor is a binary system composed of a carbon-oxygen star and a neutron star (NS) companion. The gravitational collapse leads to a type Ic supernova (SN) explosion and triggers an accretion process onto the NS. For orbital periods of a few minutes, the NS reaches the critical mass and forms a black hole (BH). Two physical situations produce MeV neutrinos. First, during the accretion, the NS surface emits neutrino–antineutrino pairs by thermal production. We calculate the properties of such a neutrino emission, including flavor evolution. Second, if the angular momentum of the SN ejecta is high enough, an accretion disk might form around the BH. The disk’s high density and temperature are ideal for MeV-neutrino production. We estimate the flavor evolution of electron and non-electron neutrinos and find that neutrino oscillation inside the disk leads to flavor equipartition. This effect reduces (compared to assuming frozen flavor content) the energy deposition rate of neutrino–antineutrino annihilation into electron–positron ($e^{+}{e}^{-}$) pairs in the BH vicinity. We then analyze the production of GeV-TeV neutrinos around the newborn black hole. The magnetic field surrounding the BH interacts with the BH gravitomagnetic field producing an electric field that leads to spontaneous $e^{+}{e}^{-}$ pairs by vacuum breakdown. The $e^{+}{e}^{-}$ plasma self-accelerates due to its internal pressure and engulfs protons during the expansion. The hadronic interaction of the protons in the expanding plasma with the ambient protons leads to neutrino emission via the decay chain of $\pi$-meson and $\mu$-lepton, around and far from the black hole, along different directions. These neutrinos have energies in the GeV-TeV regime, and we calculate their spectrum and luminosity. We also outline the detection probability by some current and future neutrino detectors. Full article

The Taishan Antineutrino Observatory (TAO or JUNO-TAO) is a satellite detector for the Jiangmen Underground Neutrino Observatory (JUNO). JUNO aims at simultaneously probing the two main frequencies of three-flavor neutrino oscillations, as well as their interference related to the mass ordering, at a distance of ~53 km from two powerful nuclear reactor complexes in China. Located near the Taishan-1 reactor, TAO independently measures the antineutrino energy spectrum of the reactor with unprecedented energy resolution. The TAO experiment will realize a neutrino detection rate of about 2000 per day. In order to achieve its goals, TAO is relying on cutting-edge technology, both in photosensor and liquid scintillator (LS) development which is expected to have an impact on future neutrino and Dark Matter detectors. In this paper, the design of the TAO detector with a special focus on calorimetry is discussed. In addition, an overview of the progress currently being made in the R&D for a photosensor and LS technology in the frame of the TAO project will be presented. Full article

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose experiment under construction in southern China; detector completion is expected in 2023. JUNO is a homogeneous calorimeter consisting of a target mass of 20 kt of an organic liquid scintillator, aiming to detect antineutrinos from reactors to investigate the neutrino oscillation mechanism. The scintillation and Cerenkov light emitted after the interaction of antineutrinos with the liquid scintillator is seen by a compound system of 20 inch large PMTs and 3 inch small PMTs, with a total photo-coverage of 78%. A dual-calorimetry technique is developed based on the presence of the two independent photosensor systems which are characterized by different average light level regimes, resulting in different dynamic ranges. Thanks to this novel technique, an unprecedented high light yield, and in combination with a comprehensive multiple-source and multi-position calibration campaign, JUNO is expected to reach energy-related systematic uncertainties below 1% and an effective energy resolution of 3% at 1%, required for the neutrino oscillation analysis. Full article

It is well known that the observations of neutrinoless double-beta decay prove the Majorana nature of the neutrino. However, with specific values of Majorana phases, the effective Majorana neutrino mass to be estimated from the observation of neutrinoless double-beta decay experiments is strongly suppressed if the neutrino mass pattern adheres to a normal ordering. In this case, double-beta decay might not be observed even though the neutrino is Majorana in nature. We show if neutrinos oscillate to antineutrinos in their propagation; then, the observation of this oscillation proves that neutrinos are Majorana and will provide a measurement of neutrino masses and Majorana phases. Full article

Neutrinos are a powerful tool for searching physics beyond the standard model of elementary particles. In this review, we present the status of the research on charge-parity-time (CPT) symmetry and Lorentz invariance violations using neutrinos emitted from the collapse of stars such as supernovae and other astrophysical environments, such as gamma-ray bursts. Particularly, supernova neutrino fluxes may provide precious information because all neutrino and antineutrino flavors are emitted during a burst of tens of seconds. Models of quantum gravity may allow the violation of Lorentz invariance and possibly of CPT symmetry. Violation of Lorentz invariance may cause a modification of the dispersion relation and, therefore, in the neutrino group velocity as well in the neutrino wave packet. These changes can affect the arrival time signal registered in astrophysical neutrino detectors. Direction or time-dependent oscillation probabilities and anisotropy of the neutrino velocity are manifestations of the same kind of new physics. CPT violation, on the other hand, may be responsible for different oscillation patterns for neutrino and antineutrino and unconventional energy dependency of the oscillation phase or of the mixing angles. Future perspectives for possible CPT and Lorentz violating systems are also presented. Full article

Two anomalies at nuclear reactors, one related to the absolute antineutrino flux, one related to the antineutrino spectral shape, have drawn special attention to the field of reactor neutrino physics during the past decade. Numerous experimental efforts have been launched to investigate the reliability of flux models and to explore whether sterile neutrino oscillations are at the base of the experimental findings. This review aims to provide an overview on the status of experimental searches at reactors for sterile neutrino oscillations and measurements of the antineutrino spectral shape in mid-2021. The individual experimental approaches and results are reviewed. Moreover, global and joint oscillation and spectral shape analyses are discussed. Many experiments allow setting of constraints on sterile oscillation parameters, but cannot yet cover the entire relevant parameter space. Others find evidence in favour of certain parameter space regions. In contrast, findings on the spectral shape appear to give an overall consistent picture across experiments and allow narrowing down of contributions of certain isotopes. Full article

We discuss a possibility that the so-called reactor antineutrino anomaly (RAA), which is a deficit of the ${\overline{\nu }}_e$ rates in the reactor experiments in comparison to the theoretical expectations, can at least in part be explained by applying a quantum field-theoretical approach to neutrino oscillations, which in particular predicts a small deviation from the classical inverse-square law at short (but still macroscopic) distances between the neutrino source and detector. An extensive statistical analysis of the current reactor data on the integrated ${\overline{\nu }}_e$ event rates vs. baseline is performed to examine this speculation. The obtained results are applied to study another long-standing puzzle—gallium neutrino anomaly (GNA), which is a missing ${\nu }_e$ flux from ${}^{37}$Ar and ${}^{51}$Cr electron-capture decays as measured by the gallium–germanium solar neutrino detectors GALLEX and SAGE. Full article

We show Zeeman-like splitting in the energy of spinors propagating in a background gravitational field, analogous to the spinors in an electromagnetic field, otherwise termed the Gravitational Zeeman Effect. These spinors are also found to acquire a geometric phase, in a similar way as they do in the presence of magnetic fields. However, in a gravitational background, the Aharonov-Bohm type effect, in addition to Berry-like phase, arises. Based on this result, we investigate geometric phases acquired by neutrinos propagating in a strong gravitational field. We also explore entanglement of neutrino states due to gravity, which could induce neutrino-antineutrino oscillation in the first place. We show that entangled states also acquire geometric phases which are determined by the relative strength between gravitational field and neutrino masses. Full article

The extension of the Standard model by three right-handed neutrino fields exhibit appealing symmetry between left-handed and right-handed sectors, which is only violated by interactions. It can accommodate three flavor quasi-Dirac neutrino mixing scheme, which allows processes with violation of both lepton flavor and total lepton number symmetries. We propose a $6\times 6$ unitary matrix for parameterizing the mixing among three flavors of quasi-Dirac neutrino. This mixing matrix is constructed by two $3\times 3$ unitary matrices that diagonalizes the Dirac mass term in the Lagrangian. By only assuming the Standard Model $V-A$ weak interaction, it is found that probabilities of neutrino oscillations among active flavor states and effective masses measured by single beta decay, by neutrinoless double-beta decay and by cosmology only depend on single $3\times 3$ unitary matrix relevant to mixing of active neutrino flavors. Further, by considering $1\sigma$ and $3\sigma$ uncertainties in the measured oscillation probability of electron antineutrino from reactor, derivation of the constraint on the Majorana neutrino mass component is demonstrated. The consequence for effective Majorana neutrino mass governing the neutrinoless double-beta decay is discussed. Full article

After a long a glorious history, marked by the first direct proofs of neutrino existence and of the mixing between the first and third neutrino generations, the reactor antineutrino experiments are still well alive and will continue to give important contributions to the development of elementary particle physics and astrophysics. In parallel to the SBL (short baseline) experiments, that will be dedicated mainly to the search for sterile neutrinos, a new kind of experiments will start playing an important role: reactor experiments with a “medium” value, around 50 km, of the baseline, somehow in the middle between the SBL and the LBL (long baselines), like KamLAND, which in the recent past gave essential contributions to the developments of neutrino physics. These new medium baseline reactor experiments can be very important, mainly for the study of neutrino mass ordering. The first example of this kind, the liquid scintillator JUNO experiment, characterized by a very high mass and an unprecedented energy resolution, will soon start data collecting in China. Its main aspects are discussed here, together with its potentialities for what concerns the mass ordering investigation and also the other issues that can be studied with this detector, spanning from the accurate oscillation parameter determination to the study of solar neutrinos, geoneutrinos, atmospheric neutrinos and neutrinos emitted by supernovas and to the search for signals of potential Lorentz invariance violation. Full article