Session M12: Minisymposium: Low Energy Neutrinos VI: Astrophysical Neutrinos & Detector Technology

Big Bang Nucleosynthesis, the Cosmic Neutrino Background, and Beyond Standard Model Physics During the Weak Decoupling Epoch

Big Bang Nucleosynthesis (BBN) couples nuclear astrophysics with cosmological models, weak interaction physics, and possibly Beyond Standard Model (BSM) physics. While BBN is often viewed as a concordance between independent cosmological observations and theory, the long-standing lithium problem and a newly considered helium anomaly raise intriguing questions. Improved sensitivities in cosmic microwave background observations and from 30 meter-class telescopes coupled with improvements in measuring nuclear reaction rates bring forth the interesting possibility that BBN may probe physics beyond the Standard Model and/or beyond the standard cosmological model. This talk will explore the effects of the decay of sterile neutrinos during the weak decoupling epoch into Standard Model particles, including active neutrinos. BBN is sensitive to the interplay between nuclei, the neutrino sector, and time-temperature relation around this epoch in the early universe. The result is that BBN is a sensitive probe to BSM physics relevant in this epoch.   

Evolution of Tau-Neutrino Lepton Number in Protoneutron Stars due to Active-Sterile Neutrino Mixing

We present an approximate treatment of the mixing between active-steile states in protoneutron stars created in core-collapse supernovae. Including production of sterile neutrinos through both resonant flavor conversion and collisions, we track the evolution of the tau-neutrino lepton number due to both escape of sterile neutrinos and diffusion. Our approach provides a reasonable treatment of the pertinent processes discussed in previous studies and serves a pedagogical purpose to elucidate the relevant physics. We also discuss refinements needed to study more accurately how flavor mixing with sterile neutrinos affects protoneutron star evolution.   

Measurement of neutron-oxygen interaction cross section using neutron beam for diffuse supernova neutrino background search

In 2020, Super-Kamiokande started introducing Gadolinium sulfate into the detector in order to detect neutrons more efficiently (SK-Gd) . One of the main purpose of SK-Gd is the first observation of Diffuse Supernova Neutrino Background (DSNB) using Inverse Beta Decay (IBD) events. In the SK-Gd, we can distinguish the IBD from background which do not emit neutrons thanks to high efficiency of the neutron detection.

Neutral Current Quasierastic scattering (NCQE) by atmospheric neutrinos is one of the main background of DSNB search in SK-Gd. NCQE interaction also emit neutrons, so this event cannot be distinguished from IBD by neutron detection. We have to estimate the number of NCQE events by simulation. However, the estimation has large uncertainty because the reaction of neutron with a few hundred’s of MeV via oxygen nucleus is poorly understood.

Therefore, we conducted the experiment which measure reaction of neutron and oxygen nucleus, at the Research Center for Nuclear Physics, Osaka University on October 30, and December 16, 2018. In this experiment, neutrons with 250 MeV and 30 MeV are irradiated to water target, and gamma-rays emitted from the reaction were measured. As the result of this experiment, we extracted the probability of each gamma-ray emissions. In this presentation, the results of 250 MeV experiment will be presented.   

Core-collapse supernovae - ideal physics laboratories

Core-collapse supernovae are one of the most fascinating and mysterious phenomena in the universe. These dramatic explosions of dying stars are also powerful sources of neutrinos, the most elusive particles known. Detection of supernova neutrinos offers a unique opportunity to explore physics in extreme conditions not accessible on Earth. However, despite the detection of about twenty electron antineutrinos from SN 1987 A, we are yet to test even the most fundamental prediction about the neutrino emission, namely that different neutrino flavors share a comparable amount of the released energy during the collapse. To address this challenge, existing and upcoming neutrino detectors offer the potential to register significantly more neutrinos of all flavors from the next nearby core-collapse supernova. In this talk will showcase how the upcoming measurements of galactic supernova neutrinos and the diffuse supernova neutrino background can provide invaluable insights into the physics of core-collapse supernovae and physics byond the Standard Model, allowing us to push the frontiers of astrophysics and particle physics further.   

Observation of Supernova Neutrinos via CEvNS Glow

Coherent elastic neutrino-nucleus scattering (CEvNS) is a neutral-current process in which a neutrino scatters off an entire nucleus, depositing a tiny recoil energy. The process is important in core-collapse supernovae and also presents an opportunity for detection of the burst of neutrinos ejected in the collapse within low-threshold detectors designed for dark matter detection. Though the CEvNS process dominates low-energy interactions (tens of MeV), it produces very little energy deposition from the target nuclear recoil. The challenge of a CEvNS observation is reduced somewhat if a nearby core-collapse supernova acts as a high-flux source, producing thousands of CEvNS events in larger detector volumes over mere seconds. For detectors making use of scintillation to record particle energy loss, the effect would be a uniformly distributed, isotropic scintillation—a "CEvNS glow"—throughout the detector. This talk will summarize the prospects for supernova burst detection via CEvNS in existing and future large-scale neutrino detectors.   

Measurement of the 8B Solar Neutrino Flux in the Full Fill Phase of the SNO+ Detector

SNO+ is a kiloton-scale, multipurpose neutrino experiment located in Sudbury, Ontario, Canada. Initially filled with an ultrapure water target, SNO+ is now filled with the liquid scintillator linear alkyl benzene (LAB) loaded with the wavelength shifter 2,5-Diphenyloxazole (PPO), and will soon be loaded with Tellurium-130 to study neutrinoless double beta decay. Filling of the detector with liquid scintillator completed in April 2022, with a deployed mass of 780 kilotons of scintillator with final PPO concentration of 2.2 g/L of LAB. The favorable light yield, timing and optical properties of this scintillator cocktail allow for various interesting neutrino signals to be studied, including solar neutrinos. This work will discuss the measurement of the Boron-8 solar neutrino flux during this phase of the experiment, which continued until June 2023, when the scintillator cocktail was further optimized. The outlook for future solar neutrino studies with SNO+ will also be discussed.   

Solar Neutrino Detection with the nEXO Experiment

nEXO aims to employ a 5-tonne liquid xenon time projection chamber enriched to 90% in ¹³⁶Xe. Thanks to recent observations of long-lived excited ¹³⁶Cs states, the nEXO detector has the potential to serve as a solar neutrino observatory in addition to its primary goal of neutrino-less double beta decay detection. In this talk, I will discuss the projected capabilities of nEXO to use charged-current (ν_e, ¹³⁶Xe) interactions to measure the CNO and pep solar-neutrino fluxes, as well as the energy of the ⁷Be solar-neutrinos. I will also contextualize the expected results of these measurements relative to the current measurements made by the Borexino and KamLAND collaborations.   

Quest for Low-Energy Neutrinos with Theia

Theia is a proposed large-scale neutrino detector designed to discriminate between Cherenkov and scintillation signals in order to enable a broad physics program. The baseline design consists of a tank filled with a water-based liquid scintillator (WbLS), a novel target merging the Cherenkov signal's particle direction reconstruction with the scintillator detector's remarkable energy resolution and low detection threshold. This talk will focus on the sensitivity of Theia towards the detection of low-energy neutrinos, such as solar, geo-, reactor, supernova burst, and diffuse supernova background neutrinos. Moreover, Theia can be adapted to search for neutrinoless double-beta decay, with a sensitivity reaching the normal ordering regime of neutrino mass phase space.   

LiquidO – opaque light detection technology

LiquidO is a class of particle detection technology utilising opaque media for its light detection. The technology exploits the stochastic confinement of light in such media, which allows to identify the types of individual charged and neutral particles through the topology of their energy depositions. This technology extends the traditional scintillation detector by a vertex resolution of roughly one centimetre. At energies above a few MeV, the detector technology shows tracking capabilities and therefore offers a wide range of applications in particle physics.

In this contribution, we will present this novel technology and show results on the stochastic light confinement using the wax-based scintillator NoWaSH. We will further address current and future projects which are planning to use the opaque technology for fundamental neutrino physics, reactor monitoring, or medical physics, such as SuperChooz, AM-OTech/CLOUD, and LPET.   

Advancements in Space-Based Neutrino Detection: Exploring Voxel Integration through Lab Tests and Simulations.

Our research focuses on the development of a prototype voxel-based neutrino detector to operate in space. By studying the interaction between neutrinos and gallium mediated by the W boson, we exploit electrons ejected from the interaction to estimate the neutrino's original direction. This presentation showcases the results of lab tests conducted on GAGG:Ce scintillating crystals, including characterization of light yield, energy calibration, and timing using a phototube with gamma sources. We investigate the integration of crystals with SiPMs to collect signal data using beta and gamma sources, both individually and in specific orientations to assess beta tracking capabilities and gamma detection across multiple voxels. Additionally, we explore the potential benefits of employing multiple SiPMs per crystal for enhanced signal quality and tracking resolution. To complement the lab tests, we utilize Geant4 simulations to incorporate the obtained results and evaluate various detector geometries and detection methods. Simulation-based analyses compare the original neutrino direction with that of the ejected electron, enabling the evaluation and testing of tracking algorithms, such as linear regression, Monte Carlo methods, and other potential techniques.