MeV Neutrinos Research Articles

Publisher’s Note: Detectable MeV neutrinos from black hole neutrino-dominated accretion flows [Phys. Rev. D 93 , 123004 (2016)

Received 2 November 2020DOI:https://doi.org/10.1103/PhysRevD.102.109902© 2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasExtrasolar neutrino astronomyPhysical SystemsAccretion disk & black-hole plasmaAstronomical black holesGravitation, Cosmology & Astrophysics

Overview on solar, geo, and reactor neutrino experiments

Neutrino physics has made a substantial progress in recent years: ranging from the discovery of new phenomena, as neutrino oscillations, up to the development of milestone experimental techniques, going, at the end, hand-in-hand. Today, we are able to do precision neutrino physics, as well as we have succeeded in using neutrinos as new tools to gain information about astrophysical objects. In spite of this enormous progress, many fundamental questions remain unanswered. This contribution concentrates on low-energy MeV neutrinos emitted from our Sun, along the radioactive decays inside the Earth (geoneutrinos), and reactor neutrinos. For each of these three fields, the present-day motivation, open questions, as well as the latest experimental results and future perspectives are discussed.

Neutrinos and gravitational waves from magnetized neutrino-dominated accretion discs with magnetic coupling

ABSTRACT Gamma-ray bursts (GRBs) might be powered by black hole (BH) hyperaccretion systems via the Blandford–Znajek (BZ) mechanism or neutrino annihilation from neutrino-dominated accretion flows (NDAFs). Magnetic coupling (MC) between the inner disc and BH can transfer angular momentum and energy from the fast-rotating BH to the disc. The neutrino luminosity and neutrino annihilation luminosity are both efficiently enhanced by the MC process. In this paper, we study the structure, luminosity, MeV neutrinos, and gravitational waves (GWs) of magnetized NDAFs (MNDAFs) under the assumption that both the BZ and MC mechanisms are present. The results indict that the BZ mechanism will compete with the neutrino annihilation luminosity to trigger jets under the different partitions of the two magnetic mechanisms. The typical neutrino luminosity and annihilation luminosity of MNDAFs are definitely higher than those of NDAFs. The typical peak energy of neutrino spectra of MNDAFs is higher than that of NDAFs, but similar to those of core-collapse supernovae. Moreover, if the MC process is dominant, then the GWs originating from the anisotropic neutrino emission will be stronger particularly for discs with high accretion rates.

Neutrinos from Type Ia and Failed Core-Collapse Supernovae at Dark Matter Detectors.

Neutrinos produced in the hot and dense interior of the next galactic supernova would be visible at dark matter experiments in coherent elastic nuclear recoils. While studies on this channel have focused on successful core-collapse supernovae, a thermonuclear (type Ia) explosion, or a core collapse that fails to explode and forms a black hole, are as likely to occur as the next galactic supernova event. I show that generation-3 noble liquid-based dark matter experiments such as darwin and argo, operating at sub-keV thresholds with ionization-only signals, would distinguish between (a)leading hypotheses of type Ia explosion mechanisms by detecting an O(1) s burst of O(1) MeV neutrinos, and (b)progenitor models of failed supernovae by detecting an O(1) s burst of O(10) MeV neutrinos, especially by marking the instant of black hole formation from abrupt stoppage of neutrino detection. This detection is sensitive to all neutrino flavors and insensitive to neutrino oscillations, thereby making measurements complementary to neutrino experiments.

Expanding Core-Collapse Supernova Search Horizon of Neutrino Detectors

Core-Collapse Supernovae, failed supernovae and quark novae are expected to release an energy of few 1053 ergs through MeV neutrinos and a network of detectors is operative to look online for these events. However, when the source distance increases and/or the average energy of emitted neutrinos decreases, the signal statistics drops and the identification of these low statistic astrophysical bursts could be challenging. In a standard search, neutrino detectors characterise the observed clusters of events with a parameter called multiplicity, i.e. the number of collected events in a fixed time-window. We discuss a new parameter called ξ (=multiplicity/duration of the cluster) in order to add the information on the temporal behaviour of the expected signal with respect to background. By adding this parameter to the multiplicity we optimise the search of astrophysical bursts and we increase their detection horizon. Moreover, the use of the ξ can be easily implemented in an online system and can apply also to a network of detectors like SNEWS. For these reasons this work is relevant in the multi-messengers era when fast alerts with high significance are mandatory.

Astroparticle Physics in Hyper-Kamiokande

Hyper-Kamiokande (Hyper-K) is a proposed next generation neutrino experiment, aiming at the measurement which starts at 2027. Hyper-K project includes a high intensity accelerator neutrino beamline at J-PARC and large water Cherenkov far detectors. Each detector will provide the fiducial volume of 0.19 Mt ultra-pure water. Due to its world-largest water volume, superior performance of the new photodetector and the location at deep underground, Hyper-K will also have great capability for neutrino astrophysics and push back the frontiers. Here, the Hyper-K’s detector performance for MeV neutrinos will be shown. Then the issues for neutrino astrophysics and our reach will be discussed, i.e., for solar neutrino, supernova burst neutrino and supernova relic neutrino observations.

A Search for MeV to TeV Neutrinos from Fast Radio Bursts with IceCube

Abstract We present two searches for IceCube neutrino events coincident with 28 fast radio bursts (FRBs) and 1 repeating FRB. The first improves on a previous IceCube analysis—searching for spatial and temporal correlation of events with FRBs at energies greater than roughly 50 GeV—by increasing the effective area by an order of magnitude. The second is a search for temporal correlation of MeV neutrino events with FRBs. No significant correlation is found in either search; therefore, we set upper limits on the time-integrated neutrino flux emitted by FRBs for a range of emission timescales less than one day. These are the first limits on FRB neutrino emission at the MeV scale, and the limits set at higher energies are an order-of-magnitude improvement over those set by any neutrino telescope.

New Dark Matter Search Strategies at DUNE

If dark matter annihilates to light quarks in the core of the Sun, then a flux of 236 MeV neutrinos will be produced from the decay of stopped kaons. We consider strategies for DUNE to not only observe such a signal, but to determine the direction of the neutrino from the hadronic recoil. We show that this novel strategy can provide a better handle on systematic uncertainties associated with dark matter searches.

MeV neutrino dark matter: relic density, lepton flavour violation and electron recoil

Right-handed neutrinos with MeV to GeV mass are very promising candidates for dark matter (DM). Not only can they solve the missing satellite puzzle, the cusp-core problem of inner DM density profiles, and the too-big-to fail problem, i.e. that the unobserved satellites are too big to not have visible stars, but they can also account for the Standard Model (SM) neutrino masses at one loop. We perform a comprehensive study of the right-handed neutrino parameter space and impose the correct observed relic density and SM neutrino mass differences and mixings. We find that the DM masses are in agreement with bounds from big-bang nucleosynthesis, but that these constraints induce sizeable DM couplings to the charged SM leptons. We then point out that previously overlooked limits from current and future lepton flavour violation experiments such as MEG and SINDRUM heavily constrain the allowed parameter space. Since the DM is leptophilic, we also investigate electron recoil as a possible direct detection signal, in particular in the XENON1T experiment. We find that despite the large coupling and low backgrounds, the energy thresholds are still too high and the predicted cross sections too low due to the heavy charged mediator, whose mass is constrained by LEP limits.

Black hole accretion disk diffuse neutrino background

We study the cosmic MeV neutrino background from accretion disks formed during collapsars and the coalescence of compact-object mergers. We provide updated estimates, including detection rates, of relic neutrinos from collapsars, as well as estimates for neutrinos that are produced in mergers. Our results show that diffuse neutrinos detected at HyperK would likely include some that were emitted from binary neutron-star mergers. The collapsar rate is uncertain, but at its upper limit relic neutrinos from these sources would provide a significant contribution to the cosmic diffuse neutrino background.

On High-energy Particles in Accretion Disk Coronae of Supermassive Black Holes: Implications for MeV Gamma-rays and High-energy Neutrinos from AGN Cores

Abstract Recent observations with ALMA have revealed evidence for nonthermal synchrotron emission from the core regions of two nearby Seyfert galaxies. This suggests that the coronae of accretion disks in active galactic nuclei (AGNs) can be conducive to the acceleration of nonthermal electrons, in addition to the hot, thermal electrons responsible for their X-ray emission through thermal Comptonization. Here, we investigate the mechanism of such particle acceleration, based on observationally inferred parameters for AGN disk coronae. One possibility to account for the observed nonthermal electrons is diffusive shock acceleration, as long as the gyrofactor η g does not exceed ∼106. These nonthermal electrons can generate gamma-rays via inverse Compton scattering of disk photons, which can appear in the MeV band, while those with energies above ∼100 MeV would be attenuated via internal γγ pair production. The integrated emission from all AGNs with thermal and nonthermal Comptonization can reproduce the observed cosmic background radiation in X-rays as well as gamma-rays up to ∼10 MeV. Furthermore, if protons are accelerated in the same conditions as electrons and η g ∼ 30, our observationally motivated model is also able to account for the diffuse neutrino flux at energies below 100–300 TeV. The next generation of MeV gamma-ray and neutrino facilities can test these expectations by searching for signals from bright, nearby Seyfert galaxies such as NGC 4151 and IC 4329A.

Developing the MeV potential of DUNE: Detailed considerations of muon-induced spallation and other backgrounds

The Deep Underground Neutrino Experiment (DUNE) could be revolutionary for MeV neutrino astrophysics, because of its huge detector volume, unique event reconstruction capabilities, and excellent sensitivity to the $\nu_e$ flavor. However, its backgrounds are not yet known. A major background is expected due to muon spallation of argon, which produces unstable isotopes that later beta decay. We present the first comprehensive study of MeV spallation backgrounds in argon, detailing isotope production mechanisms and decay properties, analyzing beta energy and time distributions, and proposing experimental cuts. We show that above a nominal detection threshold of 5-MeV electron energy, the most important backgrounds are --- surprisingly --- due to low-A isotopes, such as Li, Be, and B, even though high-A isotopes near argon are abundantly produced. We show that spallation backgrounds can be powerfully rejected by simple cuts, with clear paths for improvements. We compare these background rates to rates of possible MeV astrophysical neutrino signals in DUNE, including solar neutrinos (detailed in a companion paper [Capozzi et al. arXiv:1808.08232 [hep-ph]]), supernova burst neutrinos, and the diffuse supernova neutrino background. Further, to aid trigger strategies, in the Appendixes we quantify the rates of single and multiple MeV events due to spallation, radiogenic neutron capture, and other backgrounds, including through pileup. Our overall conclusion is that DUNE has high potential for MeV neutrino astrophysics, but reaching this potential requires new experimental initiatives.

Multimessenger tests of Einstein's weak equivalence principle and Lorentz invariance with a high-energy neutrino from a flaring blazar

The detection of the high-energy (∼290 TeV) neutrino coincident with the flaring blazar TXS 0506+056, the first and only 3σ neutrino-source association to date, provides new, multimessenger tests of the weak equivalence principle (WEP) and Lorentz invariance. Assuming that the flight time difference between the TeV neutrino and gamma-ray photons from the blazar flare is mainly caused by the gravitational potential of the Laniakea supercluster of galaxies, we show that the deviation from the WEP for neutrinos and photons is conservatively constrained to have an accuracy of 10−6–10−7, which is 3–4 orders of magnitude better than previous results placed by MeV neutrinos from supernova 1987A. In addition, we demonstrate that the association of the TeV neutrino with the blazar flare sets limits on the energy scales of quantum gravity for both linear and quadratic violations of Lorentz invariance (LIV) to EQG,1>3.2×1015–3.7×1016 GeV and EQG,2>4.0×1010–1.4×1011 GeV. These improve previous limits on both linear and quadratic LIV energy scales in neutrino propagation by 5–7 orders of magnitude.

Could a Hypercritical Accretion be Associated with the Atypical Magnetic-field Behavior in RX J0822-4300?

Recent X-ray observations in the central compact remnant of Puppis A and other young pulsars have provided convincing evidence about the anti-magnetar nature of the so-called central compact objects (CCOs). The measured period derivative, corrected by the proper movement, provides exceptionally low superficial magnetic fields for such sources. Using the dipole radiation canonical model, the superficial magnetic field of the CCO (RX J0822-4300) in Puppis A was estimated to be B ≃ 2.9 × 1010 G. In this paper, we present a numerical model to interpret the unusual magnetic-field behavior in RX J0822-4300. Using the magnetohydrodynamic simulations during the hypercritical accretion phase, we propose that a variety of MeV neutrinos is created given evidence about the submergence of the magnetic field in the pulsar. We investigate the production, propagation, oscillations, and detection of MeV neutrinos from this source. The detection of neutrino events with their flavor ratios would be a compelling signature of the decreasing evolution of the magnetic field not only in RX J0822-4300 but also in CCO candidates.

A new solar neutrino channel for grand-unification monopole searches

We identify a previously untapped discovery channel for grand-unification monopoles, arising from their ability to catalyse the direct decay of protons into monoenergetic 459 MeV antineutrinos within the Sun. Previous analyses omit this possibility as it necessarily involves an electroweak suppression factor, and instead search for the unsuppressed 20–50 MeV neutrinos produced via two-stage proton decays. By accounting for the relative difference in interaction cross section and experimental background at typical neutrino detection experiments, we demonstrate that this new channel in fact possesses greater discovery potential. As a case in point, using 5326 live days of Super-Kamiokande exposure we find that 2 σ (3 σ) deviations in the 20–50 MeV channel are amplified to 3 σ (4.6 σ) deviations in the 459 MeV case. Exploiting correlations between these two channels may also offer even greater statistical power.

Topological track reconstruction in unsegmented, large-volume liquid scintillator detectors

Unsegmented, large-volume liquid scintillator (LS) neutrino detectors have proven to be a key technology for low-energy neutrino physics. The efficient rejection of radionuclide background induced by cosmic muon interactions is of paramount importance for their success in high-precision MeV neutrino measurements. We present a novel technique to reconstruct GeV particle tracks in LS, whose main property, the resolution of topological features and changes in the differential energy loss dE/dx, allows for improved rejection strategies. Different to common track reconstruction approaches, our method does not rely on concrete track / topology hypotheses. Instead, based on a reference point in space and time, the observed distribution of photon arrival times at the photosensors and the detector's characteristics in terms of photon production, propagation and detection (optical model), it reconstructs the voxelized distribution of optical photon emissions. Techniques from three-dimensional data analysis can then be applied to extract parameters describing the topology, e.g., the direction of a track. We performed a first performance evaluation of our method using single muon events with up to 10 GeV from a Geant4 simulation of the LENA detector. The current results indicate that our approach is competitive with existing reconstruction methods— although its full potential has not yet been exploited. We also remark on other detector technologies in astroparticle physics as well as applications in medical imaging that could benefit from the fundamental ideas of our method.

Improved Detection of Supernovae with the IceCube Observatory

The IceCube neutrino telescope monitors one cubic kilometer of deep Antarctic ice by detecting Cherenkov photons emitted from charged secondaries produced when neutrinos interact in the ice. The geometry of the detector, which comprises a lattice of 5160 photomultipliers, is optimized for the detection of neutrinos above 100 GeV. However, at subfreezing ice temperatures, dark noise rates are low enough that a high flux of MeV neutrinos streaming through the detector may be recognized by a collective rate enhancement in all photomultipliers. This method can be used to search for the signal of core collapse supernovae, providing sensitivity competitive to Mton neutrino detectors to a supernova in our Galaxy. An online data acquisition system dedicated to supernova detection has been running for several years, but its shortcomings include limited sampling frequency and the fact that the burst energy and direction cannot be reconstructed. A recently developed offline data acquisition system allows IceCube to buffer all registered photons in the detector in case of an alert with low probability to be erroneous. By analyzing such data offline, a precision determination of the burst onset time and the characteristics of rapidly varying fluxes, as well as estimates of the average neutrino energies may be obtained. For supernovae ending in a black hole, the IceCube data can also be used to determine the direction of the burst.

Neutrinos from Supernovae

Neutrinos are fundamental particles in the collapse of massive stars. Because of their weakly interacting nature, neutrinos can travel undisturbed through the stellar core and be direct probes of the still uncertain and fascinating supernova mechanism. Intriguing recent developments on the role of neutrinos during the stellar collapse are reviewed, as well as our current understanding of the flavor conversions in the stellar envelope. The detection perspectives of the next burst and of the diffuse supernova background will be also outlined. High-energy neutrinos in the GeV-PeV range can follow the MeV neutrino emission. Various scenarios concerning the production of high-energy neutrinos are discussed.

Neutrino Oscillations within the Induced Gravitational Collapse Paradigm of Long Gamma-Ray Bursts

Abstract The induced gravitational collapse paradigm of long gamma-ray bursts associated with supernovae (SNe) predicts a copious neutrino–antineutrino ( ) emission owing to the hypercritical accretion process of SN ejecta onto a neutron star (NS) binary companion. The neutrino emission can reach luminosities of up to 1057 MeV s−1, mean neutrino energies of 20 MeV, and neutrino densities of 1031 cm−3. Along their path from the vicinity of the NS surface outward, such neutrinos experience flavor transformations dictated by the neutrino-to-electron-density ratio. We determine the neutrino and electron on the accretion zone and use them to compute the neutrino flavor evolution. For normal and inverted neutrino mass hierarchies and within the two-flavor formalism ( ), we estimate the final electronic and nonelectronic neutrino content after two oscillation processes: (1) neutrino collective effects due to neutrino self-interactions where the neutrino density dominates, and (2) the Mikheyev–Smirnov–Wolfenstein effect, where the electron density dominates. We find that the final neutrino content is composed by ∼55% (∼62%) of electronic neutrinos, i.e., , for the normal (inverted) neutrino mass hierarchy. The results of this work are the first step toward the characterization of a novel source of astrophysical MeV neutrinos in addition to core-collapse SNe and, as such, deserve further attention.

Quasi-elastic neutrino reactions on carbon and lead nuclei

We examine neutral-current quasi-elastic neutrino–nucleus reactions on 12C and 208Pb targets. We use the relativistic mean field theory approach to describe the nuclear dynamics. We compute the cross sections for the scattering of 150, 500 and 1000 MeV neutrinos on a 12C target and study the effect of the strange-quark content of the nucleon which appears in these reactions via the isoscalar weak current. We compare our results with the data of the MiniBooNE experiment for mineral oil (CH2). We also calculate the cross section for the quasi-elastic neutron knockout reaction of 20–60 MeV neutrinos on a 208Pb target which is relevant to plans to use lead as a target material in future supernova neutrino detectors.