Session G08: Neutrino Experiments: Backgrounds, Calibration, and Instrumentation

A Model for the Global Quantum Efficiency for a TPB-based Wavelength-Shifting System used with Photomultiplier Tubes in Liquid Argon in MicroBooNE

The MicroBooNE detector uses scintillation light from particle interactions in liquid argon as a data acquisition trigger. This scintillation light has wavelengths in the vacuum ultra violet (VUV) range, and must be converted into visible light to be detected by photomultiplier tubes (PMTs). To convert the light, MicroBooNE uses wavelength shifting plates coated with Tetraphenyl butadiene (TPB) placed in front of its PMTs. While basic tuning of this plate-PMT system is sufficient for triggering, precise calibration of the system makes additional calorimetry possible. This talk will outline how a photon simulation which accounts for the geometry and optical details of the MicroBooNE detector can accompany a measurement of observed photoelectrons in a plate-PMT test stand, and how the results may be used to determine a ``global quantum efficiency'' for the plate-PMT system. This global quantum efficiency is one required ingredient for improving the capabilities of the light collection system.   

Simulated Optical Efficiency of the IceCUBE Matryoshka WOM

The IceCUBE Neutrino Observatory is designed to detect high-energy neutrinos of astrophysical origin via Cherenkov radiation detectors located deep within the Antarctic ice. The Wavelength-shifting Optical Module (WOM), a Cherenkov light detector with scalable photosensitive area and very low noise has been proposed to replace current detectors at IceCUBE in order to detect lower energy astrophysical neutrinos from extragalactic supernovae. The Matryoshka WOM, one possible style of WOM, consists of one WOM within a larger WOM in order to increase the overall sensitivity of the detector. I will present the methods used in a series of simulations made with the Reactor Analysis Tool (RAT) to simulate the optical efficiency of a variety of possible Matryoshka WOM configurations. I will also present the results of these simulations demonstrating how the optical efficiency of the Matryoshka WOM compares with similar Cherenkov radiation detectors.   

Improved muon background rejection at Low Energies (IceCube, DeepCore)

The IceCube experiment consists of strings of digital optical modules spread out through 1 cubic kilometer of ice. DeepCore is an infill array with higher density of strings and modules located in the bottom center of IceCube. DeepCore's increased photocathode density allows it to detect neutrinos with lower energies (as low as about 10 GeV). DeepCore data has been used in multiple analyses studying neutrino properties and oscillations. The next step in improving the sensitivity of those measurements is the reduction of the copious muon background. Currently, the background is removed with various cuts, including a veto employing the surrounding IceCube modules, and a machine learning algorithm running on event features. In this talk another promising approach and attempts to adapt it to low energy analyses will be shown. The algorithm was originally developed for IceCube's high energy neutrino search. It finds the probability of an event being a muon, using non-hit modules, individual veto regions and thousands of tracks fits for each event.   

The JUNO Calibration Systems

The Jiangmen Underground Neutrino Observatory (JUNO), a 20 kton multi-purpose underground liquid scintillator (LS) detector equipped with about 50k PMTs, is under construction at Kaiping, Guangdong Province in China. The primary scientific goal is to determine the neutrino mass hierarchy (MH). Its unprecedented energy resolution requirement of 3{\%}/$\surd $E will be the most crucial performance parameter. To help achieve this, thorough calibration of the detector is a must. A comprehensive calibration system, including a Cable Loop System, Guide Tube Calibration System, Auto Calibration Unit, and Remotely Operated Vehicle, have been designed to deploy multiple sources, to cover the entire energy range of reactor neutrinos, and to achieve a full-volume position coverage inside the detector to measure the spatial response function at different calibration energies. The energy linearity can also be studied with different gamma and electron sources. In the presentation, the design and current status of the JUNO calibration systems will be discussed, including their designs and hardware progress, as well as a simulation of on the effectiveness of this calibration program.   

Toward a CEvNS Observation With Germanium

The COHERENT Collaboration made the first ever observation of Coherent Elastic Neutrino-Nucleus Scattering (CEvNS) as reported in \textit{Science} in August 2017. CEvNS is a Standard Model process in which the cross section depends on the square of the number of neutrons in the target nucleus. Therefore, COHERENT continues to work toward measuring CEvNS on other targets to test this N$^{\mathrm{2}}$ dependence. This talk will describe studies of backgrounds for COHERENT's High-Purity germanium (HPGe) detector deployment in Neutrino Alley at the Spallation Neutron Source. D. Akimov et al, Observation of coherent elastic neutrino-nucleus scattering. \textit{Science} \textbf{357}, 1123-1126 (2017). doi:10.1126/science.124.3212.103pmid:17796274   

Reverse table reconstructions for low energy neutrinos in IceCube

IceCube is a neutrino detector formed from a km$^3$ of ice beneath the South Pole instrumented with over 5000 optical sensors (DOMs). When a neutrino interacts in the ice, secondary charged particles emit Cherenkov light, some of which is detected by DOMs and recorded as a charge-time distribution across the detector. From this, we reconstruct the primary neutrino's energy and direction. Current reconstructions simulate interactions in the ice and the DOMs' responses thereto, but this is computationally expensive since most photons emitted are not detected. In this talk, we show initial results from a new reconstruction that aims for higher accuracy and better computational efficiency than current reconstructions for $\mathcal{O}(1-100)$ GeV neutrinos. Our method works in the reverse from current methods: We simulate light coming from DOMs and record in tables information about the light at space-time coordinates in the ice. In this way, we only simulate photons that would be detected. We use these "reverse" tables and an efficient event model to arrive at the expected charge-time distribution for a hypothesis. Compared with the recorded distribution, we assign a likelihood to the hypothesis, and by tuning the model parameters, we find a maximum-likelihood hypothesis.   

Recent Developments in Calibration of the IceCube Detector

The IceCube Neutrino Observatory is a cubic kilometer of ice at the south pole instrumented with PMTs so as to function as a kiloton-scale water cherenkov detector. The scale, location, and design of the detector makes it capable of a wide array of scientific analyses, ranging from low energy neutrino-oscillation studies to high energy astrophysical neutrino point source searches. As IceCube collects more data, understanding the systematic uncertainties associated with the detector becomes increasingly important, and improvements in the modeling of these systematics can lead to a significant increase in the angular resolution of our detector. This talk will detail recent developments in IceCube detector calibration, including improvements in modeling of the Antarctic ice as well as improvements in describing PMT response. Additionally, this talk will discuss future plans for fully characterizing the angular and charge response of each individual PMT unit in the IceCube detector.   

Measurement of the neutrino-induced neutron cross section in lead at the Spallation Neutron Source

COHERENT is using the intense neutrino flux produced at the Spallation Neutron Source (SNS) to investigate coherent elastic neutrino-nucleus scattering (CEvNS). The high energy neutrinos can induce reactions in the shielding material of CEvNS detectors; in particular they can excite the nucleus that will decay by emission of neutrons, producing in this way a background for the CEvNS signal. This reaction is also interesting in other contexts; for example it has been proposed as a detection mechanism for supernova neutrinos. The HALO experiment is aiming to detect supernova neutrinos by using neutrino-induced neutrons (NINs) in lead. The NIN's cross section in lead is estimated theoretically only within a factor of $\sim 3$, so a careful measurement of the production cross section is of great importance. A dedicated apparatus for the measurement of NINs in lead has been deployed at SNS by the COHERENT collaboration aiming to make a precise measurement of the cross section. In these talk we will discuss the most recent results of the experiment.