Diffuse Supernova Neutrino Background Research Articles

Pulse shape discrimination technique for diffuse supernova neutrino background search with JUNO

Pulse shape discrimination (PSD) is widely used in particle and nuclear physics. Specifically in liquid scintillator detectors, PSD facilitates the classification of different particle types based on their energy deposition patterns. This technique is particularly valuable for studies of the diffuse supernova neutrino background (DSNB), nucleon decay, and dark matter searches. This paper presents a detailed investigation of the PSD technique, applied in the DSNB search performed with the Jiangmen Underground Neutrino Observatory (JUNO). Instead of using conventional cut-and-count methods, we employ methods based on boosted decision trees and neural networks and compare their capability to distinguish the DSNB signals from the atmospheric neutrino neutral-current background events. The two methods demonstrate comparable performance, resulting in a 50–80% improvement in signal efficiency compared to a previous study performed for JUNO (An et al. [JUNO] in J Phys G 43(3):030401, 2016). Moreover, we study the dependence of the PSD performance on the visible energy and final state composition of the events and find a significant dependence on the presence/absence of 11\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{11}$$\\end{document}C. Finally, we evaluate the impact of the detector effects (photon propagation, PMT dark noise, and waveform reconstruction) on the PSD performance.

First detailed calculation of atmospheric neutrino foregrounds to the diffuse supernova neutrino background in Super-Kamiokande

The diffuse supernova neutrino background (DSNB)—a probe of the core-collapse mechanism and the cosmic star-formation history—has not been detected, but its discovery may be imminent. A significant obstacle for DSNB detection in Super-Kamiokande (Super-K) is detector backgrounds, especially due to atmospheric neutrinos (more precisely, these are foregrounds), which are not sufficiently understood. We perform the first detailed theoretical calculations of these foregrounds in the range 16–90 MeV in detected electron energy, taking into account several physical and detector effects, quantifying uncertainties, and comparing our predictions to the 15.9 live time years of pre-gadolinium data from Super-K stages I–IV. We show that our modeling reasonably reproduces this low-energy data as well as the usual high-energy atmospheric-neutrino data. To accelerate progress on detecting the DSNB, we outline key actions to be taken in future theoretical and experimental work. In a forthcoming paper, we use our modeling to detail how low-energy atmospheric-neutrino events register in Super-K and suggest new cuts to reduce their impact. Published by the American Physical Society 2024

The Sun and core-collapse supernovae are leading probes of the neutrino lifetime

The large distances travelled by neutrinos emitted from the Sun and core-collapse supernovae together with the characteristic energy of such neutrinos provide ideal conditions to probe their lifetime, when the decay products evade detection. We investigate the prospects of probing invisible neutrino decay capitalising on the detection of solar and supernova neutrinos as well as the diffuse supernova neutrino background (DSNB) in the next-generation neutrino observatories Hyper-Kamiokande, DUNE, JUNO, DARWIN, and RES-NOVA.We find that future solar neutrino data will be sensitive to values of the lifetime-to-mass ratio τ 1/m 1 and τ 2/m 2 of 𝒪(10-1–10-2) s/eV. From a core-collapse supernova explosion at 10 kpc, lifetime-to-mass ratios of the three mass eigenstates of 𝒪(105) s/eV could be tested. After 20 years of data taking, the DSNB would extend the sensitivity reach of τ 1/m 1 to 108 s/eV. These results promise an improvement of about 6–15 orders of magnitude on the values of the decay parameters with respect to existing limits.

Contribution of Neutrino-dominated Accretion Flows to the Cosmic MeV Neutrino Background

Neutrino-dominated accretion flows (NDAFs) are one of the important MeV neutrino sources and significantly contribute to the cosmic diffuse neutrino background. In this paper, we investigate the spectrum of the diffuse NDAF neutrino background (DNNB) by fully considering the effects of the progenitor properties and initial explosion energies based on core-collapse supernova (CCSN) simulations, and estimate the detectable event rate by the Super-Kamiokande detector. We find that the predicted background neutrino flux is mainly determined by the typical CCSN initial explosion energy and progenitor metallicity. For the optimistic cases, in which the typical initial explosion energy is low, the diffuse flux of the DNNB is comparable to the diffuse supernova neutrino background, which might be detected by upcoming larger neutrino detectors, such as Hyper-Kamiokande, the Jiangmen Underground Neutrino Observatory, and the Deep Underground Neutrino Experiment. Moreover, the strong outflows from NDAFs could dramatically decrease their contribution to the neutrino background.

Supernova Burst and Diffuse Supernova Neutrino Background Simulator for Water Cherenkov Detectors

If a Galactic core-collapse supernova explosion occurs in the future, it will be critical to rapidly alert the community to the direction of the supernova by utilizing neutrino signals in order to enable the initiation of follow-up optical observations. In addition, there is anticipation that observation of the diffuse supernova neutrino background will yield discoveries in the near future, given that experimental upper limits are approaching theoretical predictions. We have developed a new supernova event simulator for water Cherenkov neutrino detectors, such as the highly sensitive Super-Kamiokande. This simulator calculates the neutrino interaction in water for two simulation purposes, individual core-collapse supernova bursts and diffuse supernova neutrino background. Based on this simulator, we can evaluate the precision in determining the location of supernovae and estimate the expected number of events related to the diffuse supernova neutrino background in Super-Kamiokande. In this paper, we describe the basic structure of the simulator and its demonstration.

XENONnT and LUX-ZEPLIN constraints on DSNB-boosted dark matter

We consider a scenario in which dark matter particles are accelerated to semi-relativistic velocities through their scattering with the Diffuse Supernova Neutrino Background. Such a subdominant, but more energetic dark matter component can be then detected via its scattering on the electrons and nucleons inside direct detection experiments. This opens up the possibility to probe the sub-GeV mass range, a region of parameter space that is usually not accessible at such facilities. We analyze current data from the XENONnT and LUX-ZEPLIN experiments and we obtain novel constraints on the scattering cross sections of sub-GeV boosted dark matter with both nucleons and electrons. We also highlight the importance of carefully taking into account Earth's attenuation effects as well as the finite nuclear size into the analysis. By comparing our results to other existing constraints, we show that these effects lead to improved and more robust constraints.

Analyzing the neutron and γ-ray emission properties of an americium–beryllium tagged neutron source

Americium–beryllium (AmBe), a well-known tagged neutron source, is commonly used for evaluating the neutron detection efficiency of detectors used in ultralow background particle physics experiments, such as reactor neutrino and diffuse supernova neutrino background experiments. In particular, AmBe sources are used to calibrate neutron tagging by selecting the 4438 keV γ-ray signal, which is simultaneously emitted with a neutron signal. Therefore, analyzing the neutron and γ-ray emission properties of AmBe sources is crucial. In this study, we used the theoretical shape of a neutron energy spectrum, which was divided into three parts, to develop models of the energy spectrum and verify the results using experimental data. We used an AmBe source to measure the energy spectra of simultaneously emitted neutrons and γ-rays and determine the emission ratio of the neutrons with and without γ-ray emission. The measured spectrum was consistent with that obtained from the simulated result, whereas the measured emission ratio was significantly different from the corresponding simulated result. Here, we also discuss the feasibility of determining the neutron emission rates from the spectra divided into three parts.

JUNO sensitivity to the annihilation of MeV dark matter in the galactic halo

We discuss JUNO sensitivity to the annihilation of MeV dark matter in the galactic halo via detecting inverse beta decay reactions of electron anti-neutrinos resulting from the annihilation. We study possible backgrounds to the signature, including the reactor neutrinos, diffuse supernova neutrino background, charged- and neutral-current interactions of atmospheric neutrinos, backgrounds from muon-induced fast neutrons and cosmogenic isotopes. A fiducial volume cut, as well as the pulse shape discrimination and the muon veto are applied to suppress the above backgrounds. It is shown that JUNO sensitivity to the thermally averaged dark matter annihilation rate in 10 years of exposure would be significantly better than the present-day best limit set by Super-Kamiokande and would be comparable to that expected by Hyper-Kamiokande.

Diffuse Neutrino Flux Based on the Rates of Core-collapse Supernovae and Black Hole Formation Deduced from a Novel Galactic Chemical Evolution Model

Fluxes of the diffuse supernova neutrino background (DSNB) are calculated based on a new modeling of galactic chemical evolution, where a variable stellar initial mass function (IMF), depending on the galaxy type, is introduced and black hole (BH) formation from the failed supernova is considered for progenitors heavier than 18M ⊙. The flux calculations are performed for different combinations of the star formation rate, nuclear equation of state, and neutrino mass hierarchy, to examine the systematic effects from these factors. In any case, our new model predicts the enhanced DSNB flux at E ν ≳ 30 MeV and E ν ≲ 10 MeV, due to more frequent BH formation and a larger core-collapse rate at high redshifts in early-type galaxies, respectively. Event rate spectra of the DSNB at a detector from the new model are shown, and the detectability at water-based Cherenkov detectors, Super-Kamiokande with a gadolinium dissolution and Hyper-Kamiokande, is discussed. In order to investigate the impacts of the assumptions in the new model, we prepare alternative models, based on different IMF forms and treatments of BH formation, and estimate the discrimination capabilities between the new and alternative models at these detectors.

Disentangling sub-GeV dark matter from the diffuse supernova neutrino background using Hyper-Kamiokande

The upcoming Hyper-Kamiokande (HyperK) experiment is expected to detect the Diffuse Supernova Neutrino Background (DSNB). This requires to ponder all possible sources of background. Sub-GeV dark matter (DM) which annihilates into neutrinos is a potential background that has not been considered so far. We simulate DSNB and DM signals, as well as backgrounds in the HyperK detector. We find that DM-induced neutrinos could indeed alter the extraction of the correct values of the parameters of interest for DSNB physics. Since the DSNB is an isotropic signal, and DM originates primarily from the Galactic centre, we show that this effect could be alleviated with an on-off analysis.

Core-collapse supernovae and neutrino properties

We highlight developments in the domain of supernova neutrinos. We discuss the importance of the future observation, by running and upcoming experiments, of the neutrino signals from the next supernova as well as of the diffuse supernova neutrino background.

Neutrino nonradiative decay and the diffuse supernova neutrino background

We revisit the possibility that neutrinos undergo nonradiative decay. We investigate the potential to extract information on the neutrino lifetime-to-mass ratio from the diffuse supernova neutrino background. To this aim, we explicitly consider the current uncertainties on the core-collapse supernova rate and the fraction of failed supernovae. We present predictions in a full $3\ensuremath{\nu}$ framework in the absence and presence of neutrino nonradiative decay, for the Super-Kamiokande+Gd, the JUNO, the Hyper-Kamiokande, and the DUNE experiments, that should observe the diffuse supernova neutrino background in the near future. Our results show the importance of a $3\ensuremath{\nu}$ treatment of neutrino decay and of identifying the neutrino mass ordering to break possible degeneracies between diffuse supernova neutrino background predictions in the presence of decay and standard physics.

Diffuse supernova neutrino background in the standard and double collapse models

The diffuse supernova neutrino background (DSNB) is a powerful future tool to constrain core-collapse explosion mechanisms without observation of a nearby event, and the corresponding signal has been calculated for a variety of collapse models. For Supernova (SN) 1987A, a peculiar double neutrino burst was detected, but models for the double collapse have never been studied in the DSNB context. Here, we fill this gap and compare the DSNB signal expected in the Standard Collapse (SC) and the Double Collapse (DC) models in various future detectors, including Hyper-Kamiokande, JUNO, DUNE and the Large Baksan Neutrino Telescope (LBNT). We calculate the spectra of diffuse neutrinos and antineutrinos in the DC model and determine the rate of registered events as a function of energy of the detected particle, taking into account detector parameters. For each detector, we estimate the corresponding uncertainties and the background and compare the signals expected for the SC and DC models. We conclude that the combination of DUNE and LBNT data will have the highest sensitivity to discriminate between the SC and DC models.

Development of ultra-pure gadolinium sulfate for the Super-Kamiokande gadolinium project

Abstract This paper reports the development and detailed properties of about 13 metric tons of gadolinium sulfate octahydrate, $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, which has been dissolved into Super-Kamiokande (SK) in the summer of 2020. We evaluate the impact of radioactive impurities in $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ on diffuse supernova neutrino background searches and solar neutrino observation and confirm the need to reduce radioactive and fluorescent impurities by about three orders of magnitude from commercially available high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$. In order to produce ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, we have developed a method to remove impurities from gadolinium oxide, Gd2O3, consisting of acid dissolution, solvent extraction, and pH control processes, followed by a high-purity sulfation process. All of the produced ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ is assayed by inductively coupled plasma mass spectrometry and high-purity germanium detectors to evaluate its quality. Because of the long measurement time of high-purity germanium detectors, we have employed several underground laboratories for making parallel measurements including the Laboratorio Subterráneo de Canfranc in Spain, Boulby in the UK, and Kamioka in Japan. In the first half of production, the measured batch purities were found to be consistent with the specifications. However, in the latter half, the $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ contained one order of magnitude more 228Ra than the budgeted mean contamination. This was correlated with the corresponding characteristics of the raw material Gd2O3, in which an intrinsically large contamination was present. Based on their modest impact on SK physics, they were nevertheless introduced into the detector. To reduce 228Ra for the next stage of gadolinium loading to SK, a new process has been successfully established.

Probing non-standard neutrino interactions with a light boson from next galactic and diffuse supernova neutrinos

Non-standard neutrino interactions with a massive boson can produce the bosons in the core of core-collapse supernovae (SNe). After the emission of the bosons from the SN core, their subsequent decays into neutrinos can modify the SN neutrino flux. We show future observations of neutrinos from a next galactic SN in Super-Kamiokande (SK) and Hyper-Kamiokande (HK) can probe flavor-universal non-standard neutrino couplings to a light boson, improving the previous limit from the SN 1987A neutrino burst by several orders of magnitude. We also discuss sensitivity of the flavor-universal non-standard neutrino interactions in future observations of diffuse neutrinos from all the past SNe, known as the diffuse supernova neutrino background (DSNB). According to our analysis, observations of the DSNB in HK, JUNO and DUNE experiments can probe such couplings by a factor of ∼ 2 beyond the SN 1987A constraint. However, our result is also subject to a large uncertainty concerning the precise estimation of the DSNB.

Rocks, water, and noble liquids: Unfolding the flavor contents of supernova neutrinos

Measuring core-collapse supernova neutrinos, both from individual supernovae within the Milky Way and from past core collapses throughout the Universe (the diffuse supernova neutrino background, or DSNB), is one of the main goals of current and next generation neutrino experiments. Detecting the heavy-lepton flavor (muon and tau types, collectively ${\ensuremath{\nu}}_{x}$) component of the flux is particularly challenging due to small statistics and large backgrounds. While the next galactic neutrino burst will be observed in a plethora of neutrino channels, allowing us to measure a small number of ${\ensuremath{\nu}}_{x}$ events, only upper limits are anticipated for the diffuse ${\ensuremath{\nu}}_{x}$ flux even after decades of data taking with conventional detectors. However, paleo detectors could measure the time-integrated flux of neutrinos from galactic core-collapse supernovae via flavor-blind neutral current interactions. In this work, we show how combining a measurement of the average galactic core-collapse supernova flux with paleo detectors and measurements of the DSNB electron-type neutrino fluxes with the next-generation water Cherenkov detector Hyper-Kamiokande and the liquid noble gas detector DUNE will allow to determine the mean supernova ${\ensuremath{\nu}}_{x}$ flux parameters with precision of order ten percent. Realizing this potential requires both the cosmic supernova rate out to $z\ensuremath{\sim}1$ and the integrated Galactic supernova rate over the last $\ensuremath{\sim}1\text{ }\text{ }\mathrm{Gyr}$ to be established at the $\ensuremath{\sim}10%$ level.

Neutrino secret self-interactions: A booster shot for the cosmic neutrino background

Neutrinos might interact among themselves through forces that have so far remained hidden. Throughout the history of the Universe, such secret interactions could lead to scatterings between the neutrinos from supernova explosions and the nonrelativistic relic neutrinos left over from the big bang. Such scatterings can boost the cosmic neutrino background ($\mathrm{C}\ensuremath{\nu}\mathrm{B}$) to energies of $\mathcal{O}(\mathrm{MeV})$, making it, in principle, observable in experiments searching for the diffuse supernova neutrino background. Assuming a model-independent, but flavor universal, four-Fermi interaction, we determine the upscattered cosmic neutrino flux, and derive constraints on such secret interactions from the latest results from Super-Kamiokande. Furthermore, we also study prospects for detection of the boosted flux in future lead-based coherent elastic neutrino-nucleus scattering experiments. Nevertheless, given current constraints on flavor universal self-interactions, we find that the upscattered $\mathrm{C}\ensuremath{\nu}\mathrm{B}$ contribution to the total DSNB flux is negligible, making a possible measurement of the boosted $\mathrm{C}\ensuremath{\nu}\mathrm{B}$ insurmountable.

Diffuse supernova neutrino background as a probe of late-time neutrino mass generation

The relic neutrinos from old supernova explosions are among the most ancient neutrino fluxes within experimental reach. Thus, the diffuse supernova neutrino background (DSNB) could teach us if neutrino masses were different in the past (redshifts $z\ensuremath{\lesssim}5$). Oscillations inside the supernova depend strongly on the neutrino mass-squared differences and the values of the mixing angles, rendering the DSNB energy spectrum sensitive to variations of these parameters. Considering a purely phenomenological parametrization of the neutrino masses as a function of redshift, we compute the expected local DSNB spectrum here on Earth. Given the current knowledge of neutrino oscillation parameters, especially the fact that $|{U}_{e3}{|}^{2}$ is small, we find that the ${\ensuremath{\nu}}_{e}$ spectrum could be significantly different from standard expectations if neutrinos were effectively massless at $z\ensuremath{\gtrsim}1$ as long as the neutrino mass ordering is normal. On the other hand, the ${\overline{\ensuremath{\nu}}}_{e}$ flux is not expected to be significantly impacted. Hence, a measurement of both the neutrino and antineutrino components of the DSNB should allow one to test the possibility of recent neutrino mass generation.

Dark matter pollution in the Diffuse Supernova Neutrino Background

The Hyper-Kamiokande (HyperK) experiment is expected to precisely measure the Diffuse Supernova Neutrino Background (DSNB). This requires that the backgrounds in the relevant energy range are well understood. One possible background that has not been considered thus far is the annihilation of low-mass dark matter (DM) to neutrinos. We conduct simulations of the DSNB signal and backgrounds in HyperK, and quantify the extent to which DM annihilation products can pollute the DSNB signal. We find that the presence of DM could affect the determination of the correct values of parameters of interest for DSNB physics, such as effective neutrino temperatures and star formation rates. While this opens the possibility of simultaneously characterising the DNSB and discovering dark matter via indirect detection, we argue that it would be hard to disentangle the two contributions due to the lack of angular information available at low energies.

Prospects for detecting the diffuse supernova neutrino background with JUNO

We present the detection potential for the diffuse supernova neutrino background (DSNB) at the Jiangmen Underground Neutrino Observatory (JUNO), using the inverse-beta-decay (IBD) detection channel on free protons. We employ the latest information on the DSNB flux predictions, and investigate in detail the background and its reduction for the DSNB search at JUNO. The atmospheric neutrino induced neutral current (NC) background turns out to be the most critical background, whose uncertainty is carefully evaluated from both the spread of model predictions and an envisaged in situ measurement. We also make a careful study on the background suppression with the pulse shape discrimination (PSD) and triple coincidence (TC) cuts. With latest DSNB signal predictions, more realistic background evaluation and PSD efficiency optimization, and additional TC cut, JUNO can reach the significance of 3σ for 3 years of data taking, and achieve better than 5σ after 10 years for a reference DSNB model. In the pessimistic scenario of non-observation, JUNO would strongly improve the limits and exclude a significant region of the model parameter space.