Browsing by Author "Scholberg, Kate"

Coherent Elastic Neutrino-Nucleus Scattering (CEvNS) was first measured by COHERENT in 2017 nearly 40 years after it was first proposed. The process involved measuring tiny nuclear recoils that result from a neutrino scattering off of atomic nuclei. COHERENT made the first two measurements of CEvNS at the Spallation Neutron Source (SNS) and is working toward additional measurements there with the goal of observing the dependence of the cross section on detector material. The SNS, as the name implies, is an intense neutron source. These neutrons must be fully accounted for as a background for CEvNS because they are coincident with the neutrinos and because they can leave a similar recoil signature in detectors.\\ \indent The Multiplicity And Recoil Spectrometer (MARS) was deployed at the SNS to measure neutrons. MARS takes advantage of capture-gating to identify neutrons separate from other environmental backgrounds. In order to measure neutrons at the SNS, MARS must be characterized there to assess detection efficiencies and performance. The detection efficiency for MARS was determined to be 3.9$\%$ for 14 MeV neutrons and is a function of cuts on the variables characteristic to the capture-gating method.\\ \indent In this work, other characterization measurements are detailed including trigger efficiency, light yield and resolution as a function of position, and neutron detection efficiency. A first measurement of the neutron fluence with MARS is described for its original location in Neutrino Alley. After determining cuts on the relevant variables, 179 $\pm$ 27 neutrons are used to measure a fluence of 415 neutrons/m$^2$/10$^{12}$J $\pm$15$\%_{stat}$ + $\pm$54$\%_{sys}$ of protons on target. This fluence is expectedly lower than previous measurements with other detectors as MARS was in a more neutron-quiet location. A first look at the deposited energy spectrum from these neutrons is also shown.

The growth in the neutrino sector over the last several decades has offered interesting answers to questions about the neutrino's fundamental nature and the essential role it plays in astrophysical processes. The field's success allows a trend towards bolder and more precise observations of the oft-eluding particle, and concrete cross section measurements are possible like never before. Coherent elastic neutrino-nucleus scattering (CEvNS) is a neutral-current process in which a neutrino scatters off a nucleus as a cohesive unit, depositing a tiny recoil energy (few-to-tens-of-keV). Observed for the first time by the COHERENT experiment in 2017, the clean theoretical cross section prediction allows CEvNS to function as not only a probe for non-standard interactions and nuclear form factors, but also as a predictable flavor-blind signature from all manner of sources. The process is important in core-collapse supernovae and also presents an opportunity for detection of a burst of core-collapse neutrinos in low-threshold detectors designed for solar neutrino and dark matter detection. Often partnered with neutrino beam facilities, a second trend in the field has been leveraging new technologies and techniques to scale up to the ton-scale and beyond.

The work presented here will cover the ability of ton-scale scintillators to measure CEvNS interactions with neutrinos from two sources. The first covers the prospects for flavor-blind supernova neutrino burst detection via CEvNS (E$\nu$=10s of MeV) in existing and future large scintillating detectors. This study will present an analytic method for obtaining the expected photon spectra and provide predictions on the CEvNS observation power during the exceedingly neutrino-luminous burst. The second undertaking details the deployment of COHERENT's new multi-ton NaI[Tl] subsystem, a scintillating detector designed to observe CEvNS from pulsed, stopped-pion neutrinos at the Spallation Neutron Source (also 10s of MeV). Analysis of the in-situ backgrounds of the first half-ton module is conducted to lay the foundation for a long-term CEvNS measurement on sodium.

Neutrinos represent a rich field of physics that contains many theoretical problems that are yet to be solved and experimental results hinting at physics beyond the standard model of particle physics (BSM). An experiment studying neutrino physics and that is the source of the data used in the studies presented here is COHERENT. Its primary goals are to measure and characterize coherent elastic neutrino-nucleus scattering (CEvNS). Studying CEvNS, a standard-model process, provides a direct way to constrain BSM theories. The area of Neutrino Physics that is primarily studied in this work is non-standard neutrino interactions (NSI). I use the data taken by the CsI and CENNS-10 detectors of the COHERENT experiment to improve the constraint on the vector electron-electron

NSI couplings with the up and down quarks. In addition to combining the data of those detectors, I use the Feldman-Cousins technique to improve the NSI limit, obtaining a result that is stronger than prior constraints. Multiple future improvements are discussed.

Another topic investigated here is non-zero neutrino magnetic moments, that, if measured, would point to BSM physics. I estimate the sensitivity of the future COHERENT program to the muon neutrino magnetic moment by minimizing the likelihood function of observing nuclear recoils due to that neutrino magnetic moment in the COHERENT Ge detector. The obtained predicted sensitivity is not as strong as indirect limits, but is similar to existing direct constraints.

A first measurement of $\nu_{e} + {}^{16}\text{O} \to e^{-} + {}^{16}\text{F}^{*}$ cross section from 45 MeV to 125 MeV was performed using the atmospheric neutrinos incident to the Super-Kamiokande detector over 24 years. This corresponds to an exposure of 485 kTon$\cdot$years, and 125 (after cuts) expected $\nu_{e} - {}^{16}\text{O}$ events between 45 and 125 MeV. An event generator to simulate $\nu_{e} - {}^{16}\text{O}$ interactions, a multivariate method to separate events with de-excitation gammas, and an unbinned likelihood fitter to extract the flux-weighted cross section are developed. Using these tools, a scaling factor of $1.87^{+0.35\text{(stat)}+0.62\text{(syst)}}_{-0.36\text{(stat)}-0.34\text{(syst)}}$ to the Haxton prediction was measured, corresponding to $233^{+89}_{-62}$ observed events and an atmospheric $\nu_{e}$ flux-weighted cross section of $10.8^{+4.1}_{-3.0} \times 10^{-40} \text{cm}^{2}$. This is $1.7\sigma$ larger than the Haxton prediction of $5.8 \times 10^{-40} \text{cm}^{2}$, and $3.6\sigma$ away from the null hypothesis. The measured ratio can be used to rescale the $\nu_{e} - {}^{16}\text{O}$ cross section in supernova burst studies and diffuse supernova neutrino background searches. Finally, atmospheric neutrinos at this energy range will be a background for the future WIMP dark matter searches via coherent elastic neutrino-nucleus scattering. Combined with an independent $\nu_{e} - {}^{16}\text{O}$ cross section measurement, this measurement can be used to constrain the uncertainties in the low energy atmospheric neutrino flux, which is relevant for the estimation of the WIMP neutrino floor.

We describe the measurement of muon neutrino disappearance due to

neutrino oscillation using the Tokai-2-Kamiokande (T2K) experiment's Run 1-4 (6.57×1020 POT)

data set. We analyze the data using the conventional

Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing

matrix for the three Standard Model neutrinos. The output of the

analysis is a measurement of the parameters sin2θ₂₃, Δm2₃₂ for the normal hierarchy and sin2θ₂₃, Δm2₁₃ for

the inverted hierarchy. The best-fit oscillation

parameters for the normal hierarchy are found to be

(sin2θ₂₃, Δm2₃₂) = ( 0.514, 2.51×10-3 eV2/c4}). The 90% 1D confidence interval -- determined for both parameters

using the Feldman-Cousins procedure -- is for the normal hierarchy

0.428 < sin2θ₂₃ < 0.598 and

2.34×10-3 eV2/c4 < Δm2₃₂ < 2.68\times10^{-3} eV2/c4.

For the inverted hierarchy, the best-fit oscillation parameters are

(sin2θ₂₃, Δm2₁₃) = (0.511, 2.48×10-3 eV2/c4. The 90\% 1D Feldman-Cousins confidence intervals for the inverted hierarchy are 2.31×10-3 eV2/c4 < \Delta m^2_{13} < 2.64×10-3 eV2/c4.

When a massive star reaches the end of its life, it releases 99\% of its energy in the form of neutrinos during a process known as a core-collapse supernova burst. The neutrinos are released in a prompt burst lasting several tens-of-seconds with energies in the tens-of-MeV range. They carry vital information both about neutrinos properties and also about the supernova burst mechanism. Future neutrino detectors like the Deep Underground Neutrino Experiment (DUNE) plan to perform a high-precision measurement of supernova neutrinos, specifically targeting the electron flavor component of the signal. Liquid argon detectors like DUNE will primarily observe the supernova neutrinos via the neutrino-argon charged-current inelastic ($\nu_e$CC) interaction. However, this interaction's cross section has never been measured at the energy regime relevant for supernova neutrino detection. Several theoretical models exist, but they contain discrepancies when comparing different models; the differences are significant enough to introduce biases in a supernova measurement for incorrect cross section strength assumptions. A deeper understanding of the $\nu_e$CC cross section is fundamental in fully preparing for the next core-collapse supernova burst, and current experimental endeavors at the Spallation Neutron Source present the opportunity to provide preliminary constraints and an initial measurement. In this thesis, I examine the $\nu_e$CC cross section from both a theoretical and experimental point of view. I study the impact of uncertainties in the $\nu_e$CC cross section on a future supernova neutrino measurement in DUNE, and I also use data taken by the COH-Ar-10 detector of the COHERENT collaboration to perform characterization studies for a future $\nu_e$CC measurement with COH-Ar-10.