Session KB: Neutrino Physics

$\nu_{e} - {}^{16}{O}$ Interactions in Super-Kamiokande With Low Energy Atmospheric Neutrinos

Charged current quasi-elastic scattering of electron neutrinos below 100 MeV from ${}^{16}{O}$ nucleus is not yet observed, despite being a major component of the atmospheric neutrino signal at low energies. This channel is an important background for diffuse supernova neutrino background searches (DSNB) with inverse beta decay process in water Cherenkov detectors, an additional $\nu_{e}$ detection channel in case of a supernova burst, and a possible way to probe atmospheric neutrinos at low energies that will be a background for the future WIMP dark matter searches. A study for the first observation of this interaction with 20 years of Super-Kamiokande data is currently underway. We estimate about 60 signal events in the fiducial volume of Super-Kamiokande experiment and identify $\bar{\nu}_{e} - {}^{16}{O}$ and inverse beta decay interactions from atmospheric and DSNB neutrinos as major backgrounds. We will present estimated signal and background rates, methodology and current progress of the search.   

Neutrino Fast Flavor Conversions in 1D Supernova Simulations

Until recently the neutrinos emitted from the proto-neutron star created in a core-collapse supernova explosion were not expected to undergo flavor oscillations until significantly outside of the neutrinosphere. That expectation was later challenged when non-isotropic angular distributions of the neutrinos was considered. It was found, that under certain conditions, so-called `fast flavor transformation' could occur at radii which were much closer to the core thus potentially altering the dynamics of the explosion. However, previous analysis of 1D supernova simulations did not find any instances when these conditions are prevalent. In this talk, I will first give an overview of fast flavor conversions by examining toy models which simplify the conditions for conversions to occur. I will then introduce linear stability analysis as a tool for examining more complex cases which more closely resemble supernovae, and our method of reconstructing the neutrino distribution function. Finally, I will present results indicating that fast oscillations can indeed occur in 1D supernova simulations, and suggest an explanation for why other analyses saw no such oscillations.   

Investigation of Neutron-Induced Backgrounds on 134, 136Xe at En = 5 - 8 MeV for Neutrinoless Double Beta Decay Searches

Neutrinoless double-beta decay (0$\nu\beta\beta$) studies are both the best way to determine the Majorana nature of the neutrino and determine its effective mass. The two main experiments searching for 0$\nu\beta\beta$-decay of $^{136}$Xe (Q value = 2457.8 keV) are Kamland-Zen and EXO-200. Though both experiments have enriched $^{136}$Xe targets, these targets still contain significant quantities of $^{134}$Xe. A new nuclear level was reported in $^{134}$Xe that decays to the ground state emitting a 2485.7 keV gamma ray [1]. For incident neutron energies of 2.5 – 4.5 MeV, the $\gamma$-ray production cross section for this branch was found to be on the order of 10 mb . Here, we further explore the potential neutron-induced backgrounds on both $^{134}$Xe and $^{136}$Xe for extended neutron energies from 5 to 8 MeV. We will report our preliminary results for neutron inelastic scattering on $^{134,136}$Xe in applications to 0$\nu\beta\beta$ decay searches. [1] E.E. Peters, et al., EPJ Web of Conferences, 93, 01027 (2015).   

Neutron-induced background on natural tellurium relevant to $^{\mathrm{130}}$Te 0$\nu \beta \beta $ decay searches at CUORE and SNO$+$

Gamma-ray production cross-section data have been obtained for the reactions $^{\mathrm{126,128,130}}$Te(n,n'$\gamma )$ at five mean neutron energies between 3.5 and 10 MeV. We report data for the $\gamma $-ray energy region relevant to 0$\nu \beta \beta $ decay of$^{\mathrm{\thinspace 130}}$Te with Q$_{\mathrm{\beta \beta }}$-value of 2527.515 keV. For CUORE only the $\gamma $-ray transitions of excited states of $^{\mathrm{130}}$Te at 2527.06 keV and of $^{\mathrm{126}}$Te at 2533.85 keV are of interest. For SNO$+$ with its inferior energy resolution, additional excited state decays of $^{\mathrm{130}}$Te levels at 2575.2, 2581.15, and 2607.33 keV, of $^{\mathrm{128}}$Te levels at 2494.20, 2508.06, 2516.64, 2550.52, 2571.17, 2587.14, 2598.99, and 2630.14 keV, and of $^{\mathrm{126}}$Te levels at 2496.83, 2503.55, 2577.822 and 2585.462 keV are important. The highest cross-section values were found for cascade $\gamma $-ray transitions to the ground state, while direct transitions to the ground state are very weak and have been observed only for $^{\mathrm{130}}$Te at 2607.31 keV, for $^{\mathrm{128}}$Te at 2508.04 keV, and for $^{\mathrm{126}}$Te at 2503.32 keV. However, both the CUORE and SNO$+$ detectors may not be able to distinguish between cascade transitions to the ground state and direct transitions, making especially the neutron-induced excitation of the 2527.06 keV state of $^{\mathrm{130}}$Te a potential problem for 0$\nu \beta \beta $ decay searches of $^{\mathrm{130}}$Te.   

Investigation of the QRPA method for the neutrinoless double beta decay candidate $^{136}$Xe using two-nucleon transfer.

The observation of neutrino oscillations implies that the neutrino has a finite rest mass and, as such, may possibly allow decay via the hitherto unobserved neutrinoless double beta decay. There are many major experimental efforts focused on observing this decay mode. Were the decay to be observed, its rate and calculated nuclear matrix elements would provide information on the effective neutrino mass. However, calculations of the required nuclear matrix elements are inherently difficult and often exhibit large uncertainties. Often, quasiparticle random phase approximation (QRPA) methods are used, which rely on the assumption that the initial and final states can be described as a BCS condensate. This can be tested experimentally using two-nucleon transfer, where a breakdown of the BCS assumption could manifest as a pairing vibration, or pair-correlated excited states. The proposed measurement of $^{134}$Xe($^3$He,n)$^{136}$Ba to investigate the 0$\nu\beta\beta$ decay candidate $^{136}$Xe, and the potential implications of the results will be discussed.   

Neutrino-Induced Neutron Detectors at the Spallation Neutron Source

Neutrino-nucleus interactions can produce excited nuclear states that can de-excite by emitting particles, including neutrons. Neutrino-induced neutrons (NINs) produced in common gamma shielding material, such as lead or iron, can pose a background for neutrino and dark matter experiments. Additionally, NIN production in lead is the primary mechanism for the Helium and Lead Observatory (HALO) to detect supernova neutrinos, and iron-based supernova NIN detectors have been proposed. Two detectors seeking to study NIN production in lead and iron have been deployed to the Spallation Neutron Source (SNS), where neutrinos are produced with an energy similar to that of supernova neutrinos. An overview of the detector design and current status will be presented.   

Characterizing Perovskite Nanoplatelets for Liquid Scintillator Detectors

The next generation of liquid scintillator neutrinoless double beta decay experiments will require stable loading of candidate isotopes on the kiloton scale, representing a significant chemical challenge. Nanoparticles containing the candidate isotopes provide a promising method for this loading. Additionally, the unique optical properties of nanoparticles can also enhance detection and background discrimination. Perovskite nanoplatelets are particularly attractive due to the reliability of their crystal structure and their easily-scalable synthesis. We investigate the latest generation of perovskite nanoplatelets, targeting properties relevant to detector applications: emission, light yield, maximum loading, and stability. Informed by these results, we present a plan for future development of perovskite nanoplatelets for use in particle detectors.   

(CEU) Feasibility of Proton Loading in Liquid Argon Based Scintillators

Liquid argon has proven to be an ideal detection medium for a broad range of nuclear and particle physics experiments.~ It has the capability to generate both scintillation and charge signals to readout simultaneously.~ This enables the readout of not only the energy deposition but also the spatial information of interactions.~ It would be beneficial if hydrogen could be introduced into the LAr medium. This additional proton target could potentially improve sensitivity for neutron detection, limit the number of final state interactions for neutrino physics, and improve background neutron vetoing capability for neutrinoless double-beta decay and other low-energy physics searches. Historically, the introduction of hydrogen into LAr as a hydrocarbon has failed due to the absorption of LAr scintillation by the introduced dopants.~ A promising novel detection scheme based on using the radiationless transfer of excitation energy is being investigated in a 10{\%} methane loaded liquid argon detector. The apparatus and experiment status will be presented.