Neutrino Research Articles

A commentary of “Breaking the matter-antimatter mirror symmetry”： 10 remarkable discoveries from 2020 in Nature

The T2K collaboration reported that leptons appear to violate the “particle-antiparticle mirror symmetry”, which is also known as charge-parity (CP) symmetry [1]. Leptonic CP violation can be detected with neutrinos. Neutrinos are classified into three “flavors” based on their corresponding charged leptons (electron, muon, and tau). In-flight, they can transform from one flavor to another. If CP symmetry is conserved, the oscillation probability of transition from muon neutrino to electron neutrino will be the same as the probability of transition from muon antineutrino to electron antineutrino. In the T2K experiment, neutrinos (or antineutrinos) traveled 295 km across the earth and were then detected by an underground detector at the Kamioka Laboratory in Japan. The experiment measured the oscillation probability of transition from muon neutrino to electron neutrino as well as the transition of the antineutrinos; the results ruled out CP conservation at the 95% confidence level. This could be the first time we have found an indication of the origin of matter-antimatter asymmetry in the universe.①①Original source in Chinese: Jun Cao, Breaking the matter-antimatter mirror symmetry, Bulletin of National Natural Science Foundation of China. 35 (2) (2021) 236-237.

Extracting low energy signals from raw LArTPC waveforms using deep learning techniques — A proof of concept

We investigate the feasibility of using deep learning techniques, in the form of a one-dimensional convolutional neural network (1D-CNN), for the extraction of signals from the raw waveforms produced by the individual channels of liquid argon time projection chamber (LArTPC) detectors. A minimal generic LArTPC detector model is developed to generate realistic noise and signal waveforms used to train and test the 1D-CNN, and evaluate its performance on low-level signals. We demonstrate that our approach overcomes the inherent shortcomings of traditional cut-based methods by extending sensitivity to signals with ADC values below their imposed thresholds. This approach exhibits great promise in enhancing the capabilities of future generation neutrino experiments like DUNE to carry out their low-energy neutrino physics programs.

Scattering of low energy neutrinos and antineutrinos by atomic electrons

Studies of neutrino mixing and oscillations, solar neutrinos as background in dark matter searches involving electron detection, detection of sterile neutrino warm dark matter, and of possible electromagnetic properties of neutrinos, have generated interest in the low energy O(10 keV) scattering of electron neutrinos and antineutrinos by atomic electrons where the binding of the atomic electron cannot be ignored. Of particular interest is the ionization of atoms by neutrinos and antineutrinos. Most existing calculations are based on modifications of the free electron differential cross section, which destroy the relationship between the neutrino helicities and the orbital and spin angular momenta of the atomic electrons. The present calculations maintain the full collision dynamics by formulating the scattering in configuration space using the Bound Interaction Picture, rather than the usual formulation in the Interaction Picture in momentum space as appropriate to scattering by free electrons. Energy spectra of ionization electrons produced by scattering of neutrinos and antineutrinos with energies of 5, 10, 20, and 30 keV by hydrogen, helium and neon have been calculated using Dirac central field eigenfunctions and are presented as ratios to the spectra for scattering by free electrons. Binding effects increase strongly with atomic number, are largest for low neutrino energy and, for each neutrino energy, greatest at the high electron energy end of the spectrum. The most extreme effects of binding are for 5 keV scattering by Ne where the ratios are less than 0.1. The energy spectra are calculated for both a Coulombic final electron state and a free final electron state. The results indicate that the binding effects from the continuum state of the final electron are significant and can be comparable to those arising from the bound initial electron state.

Deep Learning Strategies for ProtoDUNE Raw Data Denoising

In this work, we investigate different machine learning-based strategies for denoising raw simulation data from the ProtoDUNE experiment. The ProtoDUNE detector is hosted by CERN and it aims to test and calibrate the technologies for DUNE, a forthcoming experiment in neutrino physics. The reconstruction workchain consists of converting digital detector signals into physical high-level quantities. We address the first step in reconstruction, namely raw data denoising, leveraging deep learning algorithms. We design two architectures based on graph neural networks, aiming to enhance the receptive field of basic convolutional neural networks. We benchmark this approach against traditional algorithms implemented by the DUNE collaboration. We test the capabilities of graph neural network hardware accelerator setups to speed up training and inference processes.

Neutrino Mass Spectrum: Present Indication and Future Prospect

The fact that neutrinos are massive has been the most crucial evidence of physics beyond the Standard Model of elementary particles. To date, we still do not know how neutrinos get mass and why their mass is much smaller than that of their charged fermion cousins. The precise determination of the neutrino mass spectrum has become one of the central tasks of neutrino physics, providing critical input for understanding the nature of neutrino mass and extending our model. The present landscape of the neutrino mass spectrum is reviewed and explored in this article using data from the neutrino oscillation, cosmology, and beta decay. In addition, we discuss the possibility of relevant programs elucidating the neutrino mass spectrum in the coming decades.

Search for Solar Flare Neutrinos with the KamLAND Detector

Abstract We report the result of a search for neutrinos in coincidence with solar flares from the GOES flare database. The search was performed on a 10.8 kton-year exposure of KamLAND collected from 2002 to 2019. This large exposure allows us to explore previously unconstrained parameter space for solar flare neutrinos. We found no statistical excess of neutrinos and established 90% confidence level upper limits of 8.4 × 107 cm−2 (3.0 × 109 cm−2) on the electron antineutrino (electron neutrino) fluence at 20 MeV normalized to the X12 flare, assuming that the neutrino fluence is proportional to the X-ray intensity.

Determining the Neutrino Mass Eigenstates and the Effective Majorana Mass

This paper aims at solving several open questions in current neutrino physics: the neutrino mass hierarchy, the Dirac CP violating phase, the absolute mass of neutrinos, the nature of neutrinos (Dirac or Majorana), the Majorana matrix and the absolute value of the effective Majorana neutrino mass. In the research presented in this paper, we have shown that the precise definition of the mass splittings between neutrino mass eigenstates, done in the latest analysis of experimental data, can be of crucial importance for defining the nature of neutrino mass hierarchy. The Standard Model has three generations of fundamental matter particles. Three generations of the charged lepton mass show a hierarchical structure: mτ > mμ > me. Owing to that, there is a belief and it is considered that neutrinos may follow such hierarchical structure. In our calculations, we have also included the latest data obtained, based on the processing of measurement results, which showed that even with such data, obtained results favor the normal neutrino mass hierarchy. As for the individual neutrino mass calculated in this paper, in today’s neutrino physics it is only known that neutrino mass scale is bounded only from above, and both the Dirac and the Majorana character of neutrinos are compatible with all observations. Among some of the questions resolved in this paper, which are related to the properties of neutrinos, a positive answer was also given to the question of whether light neutrinos are self-conjugate particles or not.

Interplay of nuclear physics, effective field theories, phenomenology, and lattice QCD in neutrino physics

Experiments in neutrino physics cover a wide range—from deep inelastic scattering, over long base-line oscillation experiments and low-energy coherent neutrino–nucleus scattering (CEνNS), to searches for neutrinoless double β decay (0νββ)—yet in all cases a key aspect in interpreting the results concerns understanding neutrino–nucleus interactions. If the neutrino energy is sufficiently low, the required matrix elements can be constrained in a systematic way by the interplay of effective field theories, phenomenology, and lattice QCD. In these proceedings, we illustrate this strategy focusing on the CEνNS and 0νββ processes.

Neutrino conference turns 50

In February 1972, in the break of a regional meeting of particle physicists held in Budapest Herbert Pietschmann (Vienna), Jan Nilsson (Go¨ teborg) and George Marx (Budapest) discussed the subdued position of weak interactions at international conferences. H. Pietschmann: “For George Marx it was quite obvious that the neglect of neutrino physics at the big international conferences had to be neutralised by a dedicated international conference on neutrino physics. Instead of pushing some international committee, he took the idea in his own hands and organised a Europhysics neutrino conference in Hungary by himself.”

Development of high-resolution photographic materials of the National Research Center "Kurchatov Institute" for nuclear research

In the course of the program for the development of high-resolution photographic materials for research in neutrino physics, the possibility of obtaining a nuclear emulsion with a resolution that exceeds the known materials by 5 times has been shown. The sensitivity in such materials is maintained at a high level, sufficient for the registration of nuclear radiation. With an increase in the concentration of silver halide up to 80 wt.%, nuclear photographic materials can be used to solve many physical problems Keywords: high-resolution photographic materials, nuclear research, silver halide concentration.

Limits on Astrophysical Antineutrinos with the KamLAND Experiment

Abstract We report on a search for electron antineutrinos ( ν ¯ e ) from astrophysical sources in the neutrino energy range 8.3–30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of the liquid scintillator, we observe 18 candidate events via the inverse beta decay reaction. Although there is a large background uncertainty from neutral current atmospheric neutrino interactions, we find no significant excess over background model predictions. Assuming several supernova relic neutrino spectra, we give upper flux limits of 60–110 cm−2 s−1 (90% confidence level, CL) in the analysis range and present a model-independent flux. We also set limits on the annihilation rates for light dark matter pairs to neutrino pairs. These data improve on the upper probability limit of 8B solar neutrinos converting into ν ¯ e , P ν e → ν ¯ e < 3.5 × 10 − 5 (90% CL) assuming an undistorted ν ¯ e shape. This corresponds to a solar ν ¯ e flux of 60 cm−2 s−1 (90% CL) in the analysis energy range.

Forward neutrino fluxes at the LHC

With the upcoming Run 3 of the LHC, the FASERv and SND@LHC detectors will start a new era of neutrino physics using the far-forward high-energy neutrino beam produced in collisions at ATLAS. This emerging LHC neutrino physics program requires reliable estimates of the LHC's forward neutrino fluxes and their uncertainties. In this paper we provide a new fast-neutrino flux simulation, implemented as a RIVET module, to address this issue. We present the expected energy distributions going through the FASERv and SND@LHC detectors based on various commonly used event generators, analyze the origin of those neutrinos, and present the expected neutrino event rates.

The Nonagenarian Neutrino

December 4, 2020 marks 90 years since the concept of neutrinos was proposed as a consequence of the observed discrepancies in several experiments on radioactive decays of various isotopes. There have been great many developments in our understanding of this elusive particle over the past nine decades, also leading to several Nobel Prizes awarded to work on neutrino physics. But there are many aspects of the neutrinos that are still not completely understood, including even its actual rest mass. The neutrino still remains an enigma and we have yet to learn a lot about its different properties. This article summarises the overall picture of the current understanding of the neutrino, right from its inception.

Measurements using a prototype array of plastic scintillator bars for reactor based electron anti-neutrino detection

We report measurement of reactor based electron anti-neutrinos from a prototype array of plastic scintillator bars (mini-ISMRAN) located inside Dhruva research reactor hall, BARC. The detector setup took data for 128 days for reactor on (RON) and 51 days for reactor off (ROFF) condition. A detailed analysis procedure is developed to select the anti-neutrino candidate events based on the energy deposition, number of bars hit as well as topological event selection criteria in position and time. Each of these selection criteria are compared with Monte Carlo based simulations and further an embedding technique is used to estimate the efficiencies from a data driven background study. The obtained anti-neutrino like events in RON condition are 218 ± 50 (stat) ± 37 (sys) after background subtraction. The obtained results are compared with theoretical estimation which yields 214 ± 32 (sys) anti-neutrino events for the RON condition.

The new (g−2)μ and right-handed sneutrino dark matter

In this paper we investigate the (g−2)μ discrepancy in the context of the R-parity conserving next-to-minimal supersymmetric Standard Model plus right-handed neutrinos superfields. The model has the ability to reproduce neutrino physics data and includes the interesting possibility to have the right-handed sneutrino as the lightest supersymmetric particle and a viable dark matter candidate. Since right-handed sneutrinos are singlets, no new contributions for δaμ with respect to the MSSM and NMSSM are present. However, the possibility to have the right-handed sneutrino as the lightest supersymmetric particle opens new ways to escape Large Hadron Collider and direct detection constraints. In particular, we find that dark matter masses within 10≲mν˜R≲600 GeV are fully compatible with current experimental constraints. Remarkably, not only spectra with light sleptons are needed, but we obtain solutions with mμ˜≳600 GeV in the entire dark matter mass range that could be probed by new (g−2)μ data in the near future. In addition, dark matter direct detection experiments will be able to explore a sizable portion of the allowed parameter space with mν˜R≲300 GeV, while indirect detection experiments will be able to probe a much smaller fraction within 200≲mν˜R≲350 GeV.

Measurement of reactor antineutrino flux and spectrum at RENO

The RENO experiment reports measured flux and energy spectrum of reactor electron antineutrinos\,($\overline{\nu}_e$) from the six reactors at Hanbit Nuclear Power Plant. The measurements use 966\,094\,(116\,111)\,$\overline{\nu}_e$ candidate events with a background fraction of 2.39\%\,(5.13\%), acquired in the near\,(far) detector, from August 2011 to March 2020. The inverse beta decay (IBD) yield is measured as (5.852$\,\pm\,$0.124$) \times 10^{-43}$\,cm$^2$/fission, corresponding to 0.941\,$\pm$ 0.019 of the prediction by the Huber and Mueller (HM) model. A reactor $\overline{\nu}_e$ spectrum is obtained by unfolding a measured IBD prompt spectrum. The obtained neutrino spectrum shows a clear excess around 6\,MeV relative to the HM prediction. The obtained reactor $\overline{\nu}_e$ spectrum will be useful for understanding unknown neutrino properties and reactor models. The observed discrepancies suggest the next round of precision measurements and modification of the current reactor $\overline{\nu}_e$ models.

Running axial mass of the nucleon as a phenomenological tool for calculating quasielastic neutrino\u2013nucleus cross sections

We suggest an empirical rule-of-thumb for calculating the cross sections of charged-current quasielastic (CCQE) and CCQE-like interactions of neutrinos and antineutrinos with nuclei. The approach is based on the standard relativistic Fermi-gas model and on the notion of neutrino energy dependent axial-vector mass of the nucleon, governed by a couple of adjustable parameters, one of which is the conventional charged-current axial-vector mass. The inelastic background contributions and final-state interactions are therewith simulated using GENIE 3 neutrino event generator. An extensive comparison of our calculations with earlier and current accelerator CCQE and CCQE-like data for different nuclear targets shows good or at least qualitative overall agreement over a wide energy range. We also discuss some problematical issues common to several competing contemporary models of the CCQE (anti)neutrino–nucleus scattering and to the current neutrino interaction generators.

Improving Hyper-Kamiokande sensitivity to CP violation with high precision near detector electron neutrino cross-section measurements

The next generation long-baseline neutrino oscillation experiment, Hyper-Kamiokande, will consist of a 260 kt underground water Cherenkov detector, placed 295 km from the neutrino source at J-PARC. This is generated by a 1.3 MW proton beam striking a target. In addition, a suite of near detectors, both on and off-axis will be used. With this, Hyper-Kamiokande aims to perform precision measurements of the parameters governing neutrino oscillations, the observation of CP violation being one of the main aims of the experiment. To achieve these goals, Hyper-Kamiokande will require smaller systematic uncertainties than in any previous long-baseline experiment.Many of these systematic uncertainties are related to neutrino-nucleus interactions, and can be constrained by a detector placed close to the beam production point. For this, the Hyper-Kamiokande long-baseline programme includes an Intermediate Water Cherenkov Detector, the IWCD. This is a 500 tonne water Cherenkov detector located 1 km from the beam production point. This detector is able to move within a vertical shaft and span a range of off-axis angles relative to the beam, from 1 to 4 degrees. The combination of large target mass, precise water Cherenkov reconstruction and off-axis angle flux dependence allows for high purity and high statistics electron neutrino and electron antineutrino samples. This paper describes how this detector can be used to constrain the major systematic uncertainty affecting the measurement of CP violation at Hyper-Kamiokande: the electron neutrino and antineutrino interaction cross section.

Preface

The 17th edition of the International Conference on Topics in Astroparticle and Underground Physics (TAUP 2021) was held from August 26 through September 3, 2021. For the first time in the TAUP series, started in 1989, the conference was organized as a fully online event due to the COVID-19 pandemic and hosted by IFIC Valencia, in collaboration with other Spanish institutions. IFIC (Instituto de Física Corpuscular) is a joint research institute belonging to two institutions: the Spanish National Research Council (CSIC) and the University of Valencia.The biennial TAUP series covers recent experimental and theoretical developments in astroparticle physics. The topics discussed at the conference included Cosmology, Dark Matter, Neutrino Physics and Astrophysics, Gravitational Waves, Outreach and Education, Underground Laboratories, High-Energy Astrophysics, Cosmic Rays and Multi-messenger Astronomy, as well as the intersection of these fields.The scientific program of this fully online TAUP event consisted of invited plenary talks, contributed talks and posters, as follows- Plenary sessions: invited talks and other live activities in the morning/afternoon/evening in American/European/Asian time.- Parallel sessions: asynchronous talks selected by the session conveners, pre-recorded and available for all registered participants before the conference started. Further discussion with the speakers was possible at live topical panels. A few of these talks were selected for live Hot Topic sessions.- A virtual poster session held on an interactive platform.List of Scientific Committees, TAUP 2021 International Advisory Committee, TAUP Conferences Steering Committee, TAUP 2021 Parallel Sessions and Conveners, TAUP 2021 Program at a glance, Plenary sessions, Parallel sessions: Hot Topics, Parallel sessions: Discussion panels, List of posters are available in the pdf.

Supernova Preshock Neutronization Burst as a Probe of Nonstandard Neutrino Interactions

Abstract A core-collapse supernova (CCSN) provides a unique astrophysical site for studying neutrino–matter interactions. Prior to the shock-breakout neutrino burst during the collapse of the iron core, a preshock ν e burst arises from the electron capture of nuclei and it is sensitive to the low-energy coherent elastic neutrino–nucleus scattering (CEνNS) which dominates the neutrino opacity. Since the CEνNS depends strongly on nonstandard neutrino interactions (NSIs), which are completely beyond the standard model and yet to be determined, the detection of the preshock burst thus provides a clean way to extract the NSI information. Within the spherically symmetric general-relativistic hydrodynamic simulation for the CCSN, we investigate the NSI effects on the preshock burst. We find that the NSI can maximally enhance the peak luminosity of the preshock burst almost by a factor of three, reaching a value comparable to that of the shock-breakout burst. Future detection of the preshock burst will have critical implications on astrophysics, neutrino physics, and physics beyond the standard model.