Electron Neutrino Research Articles

Quantum Mechanics and General Relativity Identify Standard Model Particles as Black Holes

The Standard Model of particle physics does not account for charged fermion mass values and neutrino mass, or explain why only three particles are in each charge state 0, -e/3, 2e/3, and -e. These issues are addressed by treating Standard Model particles with mass m as spheres with diameter equal to their Compton wavelength l =ħ/mc, where ħ is Planck’s constant and c the speed of light, and any charge in diametrically opposed pairs ±ne/6 with n = 1, 2, or 3 at the axis of rotation on the sphere surface. Particles are ground state solutions of quantized Friedmann equations from general relativity, with differing internal gravitational constants. Energy distribution within particles identifies Standard Model particles with spheres containing central black holes with mass m, and particle spin resulting from black hole angular momentum. In each charge state, energy distribution within particles satisfies a cubic equation in l, allowing only three particles in the charge state and requiring neutrino mass. Cosmic vacuum energy density is a lower limit on energy density of systems in the universe, and setting electron neutrino average energy density equal to cosmic vacuum energy density predicts neutrino masses consistent with experiment. Relations between charged fermion wavelength solutions to cubic equations in different charge states determine charged fermion masses relative to electron mass as a consequence of charge neutrality of the universe. An appendix shows assigning charge ±e/6 to bits of information on the event horizon available for holographic description of physics in the observable universe accounts for dominance of matter over anti-matter. The analysis explains why only three Standard Models are in each charge state and predicts neutrino masses based on cosmic vacuum energy density as a lower bound on neutrino energy density.

Prospects of Fast Flavor Neutrino Conversion in Rotating Core-collapse Supernovae

Abstract There is mounting evidence that neutrinos undergo fast flavor conversion (FFC) in core-collapse supernova (CCSN). In this paper, we investigate the roles of stellar rotation on the occurrence of FFC by carrying out axisymmetric CCSN simulations with full Boltzmann neutrino transport. Our result suggests that electron neutrino lepton number (ELN) angular crossings, which are the necessary and sufficient condition to trigger FFC, preferably occur in the equatorial region for rotating CCSNe. By scrutinizing the neutrino–matter interaction and neutrino radiation field, we find some pieces of evidence that the stellar rotation facilitates the occurrence of FFC. The low-electron-fraction region in the post-shock layer expands by centrifugal force, enhancing the disparity of neutrino absorption between electron-type neutrinos (ν e) and their anti-particles ( ν ¯ e ). This has a significant impact on the angular distribution of neutrinos in momentum space, in which ν e tends to be more isotropic than ν ¯ e ; consequently, ELN crossings emerge. The ELN crossing found in this study is clearly associated with rotation, which motivates further investigation on how the subsequent FFC influences explosion dynamics, nucleosynthesis, and neutrino signals in rotating CCSNe.

Ordinary Versus Novel Particle With the Example of Their Spontaneous Transition

The bicubic equation of particle limiting velocity formalism yields three solutions c1, c2 and c3, (primary, secondary and tertiary) limiting velocities in terms of the congruent parameter  which is defined in terms of m, v, and E, respectively being particle mass, velocity and energy. The bicubic equation discriminant D is given in terms of the congruent parameter z(m). When one has z2(m) ≤ 1 with the discriminant satisfying D ≤ 0 then we are talking about limiting velocities of ordinary particles. Good examples are the relativistic particles such as electron, neutrino,etc., with luminal limiting velocity c3 = c and calculated superluminal c2, and imaginary superluminal c1, all corresponding to the real particle energy. On the specific level, the situations like these, we discuss in the muon neutrino velocities with the OPERA detector and the electron velocities from the 2010 Grab Nebula Flare. The z(m) = 1 value separates the ordinary particles from novel particles, associated with D ⪰ 0 and z2 ⪰ 1 with new novel particle limiting velocity solutions c1, c2 and c3 which depend, in addition to z(m), also on the congruent angle α(m), nonlinearly related to z(m). These solutions are discussed on the newly defined sterile neutrino which here is modeled as an ordinary particle with z2 ⪯ 1 spontaneously transiting via z(m) = 1 into the modeled novel sterile neutrino with z2 ⪰ 1. All ordinary and novel particles limiting velocities carry real particle energies; the ordinary particle limiting velocity solutions being in quadratic forms, while the novel particle limiting velocity solutions being respectively, in quadratic complex form, linear complex form, and just congruent angle α complex quadratic form.

Tau neutrino identification in atmospheric neutrino oscillations without particle identification or unitarity

The largest tau neutrino dataset to date is IceCube's atmospheric tau neutrino appearance dataset containing $>1,000$ tau neutrino and antineutrino events as determined by a fit to a standard three-flavor oscillation framework. On an event-by-event basis, however, it is impossible to know that any given event is a tau neutrino as they are identical to either an electron neutrino charged-current event or a neutral-current interaction of any active flavor. Nonetheless, we conclusively show that, using only the cascade sample even without knowledge of the oscillation parameters and without assuming that the lepton mixing matrix is unitary, tau neutrino identification is still possible and there is no viable scenario in which all of the tau neutrino candidates are actually electron neutrinos. This is primarily due to the matter effect and the tau lepton production threshold, as well as the fact that tau neutrinos are systematically reconstructed at a lower energy than electron neutrinos due to one or more outgoing neutrinos. This conclusively shows that it is possible for an atmospheric neutrino oscillation experiment to confirm that $U_{\tau1}$, $U_{\tau2}$, and $U_{\tau3}$ are not all zero even with limited particle identification.

Neutrino-electron magnetohydrodynamics in an expanding universe

We derive a new model for neutrino-plasma interactions in an expanding universe that incorporates the collective effects of the neutrinos on the plasma constituents. We start from the kinetic description of a multi-species plasma in the flat Friedmann-Robertson-Walker metric, where the particles are coupled to neutrinos through the charged- and neutral-current forms of the weak interaction. We then derive the fluid equations and specialize our model to (a) the lepton epoch, where we consider a pair electron-positron plasma interacting with electron (anti-)neutrinos, and (b) after the electron-positron annihilation, where we model an electron-proton plasma and take the limit of slow ions and inertia-less electrons to obtain a set of neutrino-electron magnetohydrodynamics (NEMHD) equations. In both models, the dynamics of the plasma is affected by the neutrino motion through a ponderomotive force and, as a result, new terms appear in the induction equation that can act as a source for magnetic field generation in the early universe. A brief discussion on the possible applications of our model is proposed.

Elastic scattering of a muon neutrino by an electron in the presence of a circularly polarized laser field

In view of the great contribution of neutrino-electron scattering to the deep understanding of electroweak interactions, we focus in this paper on the study of elastic scattering of a muon neutrino by an electron $({e}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\mu}})$ in the presence of a circularly polarized electromagnetic field. We perform our theoretical calculation within the framework of Fermi theory using the exact wave functions of charged particles in an electromagnetic field. The expression of the differential cross section (DCS) for this process is obtained analytically in the absence and presence of the laser field. The effect of the field strength and frequency on the exchange of photons as well as on the DCS is presented and analyzed. Massive neutrino effects are also included and discussed. This study, added to the previous ones, will significantly enrich our knowledge in fundamental physics.

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.

Cosmogenic background suppression at the ICARUS using a concrete overburden

The ICARUS detector will search for LSND like neutrino oscillations exposed at shallow depth to the FNAL BNB beam in the context of the SBN program. In the approved FNAL SBN experiment the impact of cosmic rays is mitigated by a 4π Cosmic Ray Tagger (CRT) detector encapsulating the TPCs inside the pit and by a ∼ 3 m concrete overburden both for the near (SBND) and the far (ICARUS) detectors. Cosmic backgrounds rejection is particularly relevant for the ICARUS detector. Due to its larger size and distance from target compared to SBND, in ICARUS the neutrino signal/cosmic background ratio is 40 times more unfavorable with in addition a greater than 3 times larger out-of-spill comics rate. In this paper, I will be addressing the question of a problematic background to genuine neutrino events especially into the electron neutrino appearance analysis by a detailed MonteCarlo calculation of the cosmic rays crossing the ICARUS detector.

Measuring high-energy neutrinos with FASERυ in the LHC Run-3

FASERυ at the Large Hadron Collider, LHC, is designed to directly detect collider neutrinos for the first time and study their cross sections at high energies, where no such measurements currently exist. The detector will be located in the far-forward region of ATLAS. Deployment on the beam collision axis maximizes the flux of all three neutrino flavors, and allows FASER to measure their interaction cross-sections in the currently unexplored TeV energy range. For electron and tau neutrinos, these measurements will extend existing cross section measurements to significantly higher energies. In 2018 we performed a pilot run with the aims of measuring particle fluxes at the proposed detector location and of possibly detecting neutrino interactions for the first time at the LHC. We installed a 30-kg lead/tungsten emulsion detector and collected data of 12.2 fb1. The analysis of this data has yielded several neutrino interaction candidates, excluding the no-signal hypothesis at the 2/sigma level. During Run-3 of the LHC starting from 2022, we will deploy an emulsion detector with a target mass of 1.1 tons, coupled with the FASER magnetic spectrometer. This would yield roughly 2000 υ e, 8000 υ μ, and 50 υ τ interacting in the detector. We present the status and prospects of FASERυ, as well as the neutrino detection in the pilot run data.

Diffuse flux of PeV neutrinos from centrifugally accelerated protons in active galactic nuclei

Evidence for high-energy astrophysical PeV neutrinos has been found in the IceCube experiment from an analysis with 7.5-year (2010–2017) data. Active galactic nuclei (AGN) are among the most prominent objects in the universe, and are widely speculated to be emitters of ultra-high-energy (UHE) cosmic rays with proton domination. Based on the standard two-step LLCD mechanism of particle acceleration, a transformation of energy occurs from AGN's central super-massive black hole (SMBH) rotation to high-energy protons. Protons can be accelerated up to energies and above, and might generate PeV neutrinos in the energy range through plausible hadronic interactions. The theoretically estimated revised extragalactic diffuse muon neutrino flux employing the “luminosity-dependent density evolution (LDDE)” model for the AGN luminosity function (LF) is found consistent with the IceCube level if only a fraction, of the total bolometric luminosity (BL) of AGN is being realizable to power the PeV neutrinos. In the Λ CDM cosmological framework with the LDDE-modeled LF and photon index distribution, about of the total BL is enough to power the IceCube neutrinos.

Low energy event classification in IceCube using boosted decision trees

The DeepCore sub-array within the IceCube Neutrino Observatory is a densely instrumented region of Antarctic ice designed to observe atmospheric neutrino interactions above 5 GeV via Cherenkov radiation. An essential aspect of any neutrino oscillation analysis is the ability to accurately identify the flavor of neutrino events in the detector. This task is particularly difficult at low energies when very little light is deposited in the detector. Here we discuss the use of machine learning to perform event classification at low energies in IceCube using a boosted decision tree (BDT). A BDT is trained using reconstructed quantities to identify track-like events, which result from muon neutrino charged current interactions. This new method improves the accuracy of particle identification compared to traditional classification methods which rely on univariate straight cuts.

Recent Neutrino Cross-section Results from MicroBooNE

MicroBooNE is a liquid argon time projection chamber that operates in the Booster Neutrino Beam at Fermilab. The detector provides high-resolution imaging of neutrino interactions with a low threshold and full angular coverage. Thanks to a high event rate and several years of continuous operation, the MicroBooNE collaboration has obtained the world’s largest dataset of neutrino-argon scattering events. A detailed understanding of these interactions, especially the impact of nuclear physics effects, will be critical to the success of future precision neutrino oscillation efforts, particularly the argon-based Deep Underground Neutrino Experiment (DUNE) and the Short-Baseline Neutrino (SBN) program. This talk presents an overview of the latest neutrino-argon cross section measurements in MicroBooNE, including measurements of protons produced in muon neutrino interactions, measurements of the electron neutrino inclusive cross section, and progress towards measurements of rare channels.

Closing the neutrino BSM gap: Physics potential of atmospheric through-going muons at DUNE

Many Beyond-Standard Model physics signatures are enhanced in high-energy neutrino interactions. To explore these signatures, ultra-large Cherenkov detectors such as IceCube exploit event samples with charged current muon neutrino interactions > 1 TeV. Most of these interactions occur below the detector volume, and produce muons that enter the detector. However, the large spacing between detectors leads to inefficiency for measuring muons with energies below or near the critical energy of 400 GeV. In response, IceCube has built a densely instrumented region within the larger detector. This provides large samples of well-reconstructed interactions that are contained within the densely instrumented region, extending up to energies of ~50 GeV. This leaves a gap of relatively unexplored atmospheric-neutrino events with energies between 50 GeV and 1 TeV in the ultra-large detectors. In this paper we point out that interesting Beyond Standard Model signatures may appear in this energy window, and that early running of the DUNE far detectors can give insight into new physics that may appear in this range.

High-energy neutrinos from X-rays flares of blazars frequently observed by the Swift X-ray Telescope

ABSTRACT Blazar flares have been suggested as ideal candidates for enhanced neutrino production. While the neutrino signal of γ-ray flares has been widely discussed, the neutrino yield of X-ray flares has received less attention. Here, we compute the predicted neutrino signal from X-ray flares detected in 66 blazars observed more than 50 times with the X-ray Telescope (XRT) on board the Neil Gehrels Swift Observatory. We consider a scenario where X-ray flares are powered by synchrotron radiation of relativistic protons, and neutrinos are produced through photomeson interactions between protons with their own synchrotron X-ray photons. Using the 1 keV X-ray light curves for flare identification, the 0.5–10 keV fluence of each flare as a proxy for the all-flavour neutrino fluence, and the IceCube point-source effective area for different detector configurations, we calculate the number of muon and antimuon neutrinos above 100 TeV expected for IceCube from each flaring source. The bulk of the neutrino events from the sample originates from flares with durations ∼1–10 d. Accounting for the X-ray flare duty cycle of the sources in the sample, which ranges between ∼2 and 24 per cent, we compute an average yearly neutrino rate for each source. The median of the distribution (in logarithm) is ∼0.03 yr−1, with Mkn 421 having the highest predicted rate 1.2 ± 0.3 yr−1, followed by 3C 273 (0.33 ± 0.03 yr−1) and PG 1553+113 (0.25 ± 0.02 yr−1). Next-generation neutrino detectors together with regular X-ray monitoring of blazars could constrain the duty cycle of hadronic X-ray flares.

Sterile Neutrinos with Neutrino Telescopes

Searches for light sterile neutrinos are motivated by the unexpected observation of an electron neutrino appearance in short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and the Mini Booster Neutrino Experiment (MiniBooNE). In light of these unexpected results, a campaign using natural and anthropogenic sources to find the light (mass-squared-difference around 1 eV2) sterile neutrinos is underway. Among the natural sources, atmospheric neutrinos provide a unique gateway to search for sterile neutrinos due to the broad range of baseline-to-energy ratios, L/E, and the presence of significant matter effects. Since the atmospheric neutrino flux rapidly falls with energy, studying its highest energy component requires gigaton-scale neutrino detectors. These detectors—often known as neutrino telescopes since they are designed to observe tiny astrophysical neutrino fluxes—have been used to perform searches for light sterile neutrinos, and researchers have found no significant signal to date. This brief review summarizes the current status of searches for light sterile neutrinos with neutrino telescopes deployed in solid and liquid water.

Collective fast neutrino flavor conversions in a 1D box: Initial conditions and long-term evolution

We perform numerical simulations of fast collective neutrino flavor conversions in an one-dimensional box mimicking a system with the periodic boundary condition in one spatial direction and translation symmetry in the other two dimensions. We evolve the system over several thousands of the characteristic timescale (inverse of the interaction strength) with different initial $\bar\nu_e$ to $\nu_e$ number density ratios and different initial seed perturbations. We find that small scale structures are formed due to the interaction of the flavor waves. This results in nearly flavor depolarization in a certain neutrino phase space, when averaged over the entire box. Specifically, systems with initially equal number of $\nu_e$ and $\bar\nu_e$ can reach full flavor depolarization for the entire neutrino electron lepton number ($\nu$ELN) angular spectra. For systems with initially unequal $\nu_e$ and $\bar\nu_e$, flavor depolarization can only be reached in one side of the $\nu$ELN spectra, dictated by the net neutrino $e-x$ lepton number conservation. Quantitatively small differences depending on the initial perturbations are also found when different perturbation seeds are applied. Our numerical study here provides new insights for efforts aiming to include impact of fast flavor conversions in astrophysical simulations while calls for better analytical understanding accounting for the evolution of fast flavor conversions.

Measuring muon tracks in Baikal-GVD using a fast reconstruction algorithm

The Baikal Gigaton Volume Detector (Baikal-GVD) is a km^3-scale neutrino detector currently under construction in Lake Baikal, Russia. The detector consists of several thousand optical sensors arranged on vertical strings, with 36 sensors per string. The strings are grouped into clusters of 8 strings each. Each cluster can operate as a stand-alone neutrino detector. The detector layout is optimized for the measurement of astrophysical neutrinos with energies of sim 100 TeV and above. Events resulting from charged current interactions of muon (anti-)neutrinos will have a track-like topology in Baikal-GVD. A fast chi ^2-based reconstruction algorithm has been developed to reconstruct such track-like events. The algorithm has been applied to data collected in 2019 from the first five operational clusters of Baikal-GVD, resulting in observations of both downgoing atmospheric muons and upgoing atmospheric neutrinos. This serves as an important milestone towards experimental validation of the Baikal-GVD design. The analysis is limited to single-cluster data, favoring nearly-vertical tracks.

Follow-up of the IceCube alerts with the Baikal-GVD telescope

The high-energy muon neutrino events of the IceCube telescope, that are triggered as neutrino alerts in one of two probability ranks of astrophysical origin, “gold” and “bronze”, have been followed up by the Baikal-GVD in a fast quasi-online mode since September 2020. Search for correlations between alerts and GVD events reconstructed in two modes, muon-track and cascades (electromagnetic or hadronic showers), for the time windows ±1 h and ±12 h does not indicate statistically significant excess of the measured events over the expected number of background events. Upper limits on the neutrino fluence will be presented for each alert.

Data reduction for a calorimetrically measured ^{163}mathrm {Ho} spectrum of the ECHo-1k experiment

The electron capture in ^{163}mathrm {Ho} experiment (ECHo) is designed to directly measure the effective electron neutrino mass by analysing the endpoint region of the ^{163}mathrm {Ho} electron capture spectrum. We present a data reduction scheme for the analysis of high statistics data acquired with the first phase of the ECHo experiment, ECHo-1k, to reliably infer the energy of ^{163}mathrm {Ho} events and discard triggered noise or pile-up events. On a first level, the raw data is filtered purely based on the trigger time information of the acquired signals. On a second level, the time profile of each triggered event is analysed to identify the signals corresponding to a single energy deposition in the detector. We demonstrate that events not belonging to this category are discarded with an efficiency above 99.8%, with a minimal loss of ^{163}mathrm {Ho} events of about 0.7%. While the filter using the trigger time information is completely energy independent, a slight energy dependence of the filter based on the time profile is precisely characterised. This data reduction protocol will be important to minimise systematic errors in the analysis of the ^{163}mathrm {Ho} spectrum for the determination of the effective electron neutrino mass.

Unraveling the Dirac neutrino with cosmological and terrestrial detectors

We point out a correlation between the effective number of relativistic degrees of species Neff, the cosmologically measured mν,sterileeff, and the terrestrially measured neutrino mass sum and effective electron neutrino mass, Σmν and mνe, which arises in the Dirac neutrino hypothesis. If the neutrinos are Dirac particles, and if the active neutrinos' sterile partners were once thermalized in the early universe, then this new cosmological relic would simultaneously contribute to the effective number of relativistic species, Neff, and also lead to a correlation between the cosmologically-measured effective sterile neutrino mass mν,sterileeff and the terrestrially-measured active neutrino mass sum Σmν. We emphasize that specifically correlated deviations in Neff≳3, mν,sterileeff and Σmν above their standard predictions could be the harbinger revealing the Dirac nature of neutrinos. We provide several benchmark examples, including Dirac leptogenesis, that predict a thermal relic population of the sterile partners, and we discuss the relevant observational prospects with current and near-future experiments. If the correlation highlighted in this work is observed in future surveys, it could be interpreted as supporting evidence of Dirac neutrino masses.