Session SF: Neutrino Interactions III

Review of MINERvA's Medium Energy Neutrino Physics Program

The MINERvA experiment has completed its physics run using the 6-GeV, on-axis NuMI ME beam at Fermilab. The experiment received a total of 12E20 protons on target in both neutrino and antineutrino mode running. This allows MINERvA a new level of statistics in neutrino interaction measurements with the ability to measure multi-dimensional differential cross sections. In addition, in order to make the most of this jump in statistics, a new level of precision in flux prediction is also required. This talk will cover MINERvA’s Medium Energy (ME) physics program, including the new kinematic regimes that are now accessible, and will also discuss the exceptional precision reached in flux determination.   

Low-Energy Solar Neutrino Detection Utilizing Advanced Germanium Detectors

We prospect the possibility to use advanced germanium (Ge) detectors as a low-energy solar neutrino observatory by means of neutrino-nucleus elastic scattering. A Ge detector utilizing internal charge amplification for the charge carriers created by the ionization of impurities is a novel technology with experimental sensitivity for detecting low-energy solar neutrinos. Such a novel detector with only 1 kg of high-purity Ge will give \textasciitilde 10 events per year for pp neutrinos and \textasciitilde 4 events per year for 7 Be neutrinos with the energy threshold at 0.01 eV. We present the sensitivity of a Ge experiment for detecting solar neutrinos in the low-energy region. We show that, if germanium internal charge amplification technology becomes available, then a new opportunity arises to observe pp and 7 Be solar neutrinos. With 1 kg-year exposure, the sensitivity is equivalent to a xenon-based experiment with a detection threshold of 50 keV.   

Novelty of HPGe detector for direct detection of geo-neutrinos

Geo-neutrinos are the messengers to carry information about the interior of the Earth. Detecting geo-neutrinos is an important tool to probe the earth interior heating properties and the composition of the core of the earth. Neutrino-nucleus coherent scattering and neutrino-electron scattering are two promising methods to detect geo-neutrinos from Potassium-40, Uramium-238, and Thorium-232. Researchers have tried to detect them by using silicon, argon, water, lithium, and cadmium as target nucleus. Due to their relatively higher recoil threshold, we are still far away to detect the geo-neutrinos from Potassium-40 and Thorium-232. However, high purity germanium detector might be a novel candidate for this task primarily for two reasons. First, germanium detectors possess potential to achieve extremely low detection threshold with internal charge amplification technology. Second, it has extremely fine energy resolution which helps for better pulse shape analysis of the signals. In this paper, we present a conceptual idea on the amount of high purity germanium detector needed to detect geo-neutrinos from Potassium-40 and Thorium-232 directly over the vast backgrounds of solar neutrinos.   

\section{Electrons for Neutrinos}

The ability of current and next generation accelerator based neutrino oscillation measurements to reach their desired sensitivity requires a high-level of understanding of the neutrino-nucleus interactions. These include precise estimation of the relevant cross sections and the reconstruction of the incident neutrino energy from the measured final state particles. Incomplete understanding of these interactions can skew the reconstructed neutrino spectrum and thereby bias the extraction of fundamental oscillation parameters and searches for new physics.~ In this talk I will present new results of wide phase-space electron scattering data, collected using the CLAS spectrometer at the Thomas Jefferson National Accelerator Facility (JLab), the reconstruction of the incoming lepton energy from the measured final state is being tested. Disagreements with current event generators, used in the analysis of neutrino oscillation measurements, are observed which indicate underestimation of nuclear effects. The impact of these findings on bias in oscillation analyses will also be discussed.~   

Impact of Spectral Photon Sorting on Future Neutrino Experiments

Identifying Cherenkov photons produced when charged particles interact with scintillators provides additional information about the interaction, including directionality and particle identification, while maintaining the excellent energy and position resolution typical of scintillators. Dichroicons achieve this with a Winston cone made from dichroic filters, which reflects photons inconsistent with typical scintillation spectra to one photodetector, and passes other photons to a different photodetector. The additional information provided by Cherenkov photons detected with Dichroicons can be used to reduce backgrounds for many neutrino measurements, including low energy solar neutrinos and neutrinoless double beta decay. Here we discuss simulation studies demonstrating spectral photon sorting with Dichroicons in large liquid scintillator detectors.   

Dependence of polytetrafluoroethylene reflectance on thickness at visible and ultraviolet wavelengths in air

Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. The NEXT experiment uses PTFE inside the TPC to provide highly reflective surfaces to increase the light collection. We describe recent investigations of the dependence of PTFE reflectance on thickness in air for light of wavelengths 260~nm and 450~nm using two complementary methods. We find that PTFE reflectance for thicknesses from 5~mm to 10~mm ranges from 92.5\% to 94.5\% at 450~nm, and from 90.0\% to 92.0\% at 260~nm. Finally, we show that placing a specular reflector behind the PTFE can recover the loss of reflectance in the visible without introducing a specular component in the reflectance. These results are guiding the design choices for the NEXT-100 detector.   

Fabrication and Characterization of Mini-PPC HPGe Detector Using Crystals Grown at USD

A mini-PPC high purity germanium (HPGe) detector with amorphous germanium point contact has been made for the first time at USD. HPGe detectors are widely used in dark matter and neutrino experiments such as CDEX, TEXONO, CoGeNT, COHERENT, GERDA, Majorana, etc. In order to understand and improve the performance of HPGe detectors at various environmental and system configurations in a convenient and economic way, we are in the process of fabricating mini-PPC from HPGe that has been purified with zone refining and grown into HPGe crystals at USD. This way we avoid risking expensive commercial detectors in unconventional operating environments. We take advantage of resources, facilities, and equipment at both USD and Lawrence-Berkeley National Lab. In this presentation, we will describe the process of the fabrication and performance of the mini-PPC HPGe detector, as well as how performance can be improved in the future.   

Studies of Quantum Mechanical Coherency Effects in Neutrino-Nucleus Elastic Scattering

Neutrino-Nucleus Elastic Scattering ($\nu A_{el}$) is a well-defined process in the Standard Model of particle physics. It provides a unique laboratory to study the quantum mechanical coherency effects in electroweak interactions. We present an analytical formulation \footnote{S. Kerman et al., \textbf{Phy. Rev. D} 93, 113006 (2016)} to quantify the coherency effects ($\alpha$), relate this to nuclear form factors and experimental cross-section ratios, and characterize how its energy dependence leads to complementary among measurements at various neutrino sources with different targets. The latest results and prospects of observing $\nu A_{el}$ at the Kuo-Sheng Reactor Neutrino Laboratory with germanium detectors with $\mathcal{O}$(100 eV) threshold \footnote{A. K. Soma et al., \textbf{Nucl. Instrum. Meth. A} 67, 836 (2016)} will also be presented.