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A key enabling technology for many liquid noble gas (LNG) detectors is the use of the common wavelength shifting medium tetraphenyl butadiene (TPB). TPB thin films are used to shift ultraviolet scintillation light into the visible spectrum for detection and event reconstruction. Understanding the wavelength shifting efficiency and optical properties of these films are critical aspects in detector performance and modeling and hence in the ultimate physics sensitivity of such experiments. This article presents the first measurements of the room-temperature microphysical quantum efficiency for vacuum-deposited TPB thin films – a result that is independent of the optics of the TPB or substrate. Also presented are measurements of the absorption length in the vacuum ultraviolet regime, the secondary re-emission efficiency, and more precise results for the “black-box” efficiency across a broader spectrum of wavelengths than previous results. The low-wavelength sensitivity, in particular, would allow construction of LNG scintillator detectors with lighter elements (Ne, He) to target light mass WIMPs.

The first detection of neutrinos produced by the Sun’s secondary solar-fusion cycle paves the way for a detailed understanding of the structure of the Sun and of the formation of massive stars. Measurements of neutrinos produced by the Sun’s secondary fusion cycle.

We present the sensitivity of the Theia experiment to low-energy geo- and reactor antineutrinos. For this study, we consider one of the possible proposed designs, a 17.8-ktonne fiducial volume Theia-25 detector filled with water-based liquid scintillator placed at Sanford Underground Research Facility (SURF). We demonstrate Theia’s sensitivity to measure the geo- and reactor antineutrinos via inverse-beta decay interactions after one year of data taking with 11.9×1032 free target protons. Considering all uncertainties on input throughout the whole analysis chain, the expected number of geo- and reactor antineutrinos is 220-24+30 (stats+syst) and 168-24+26 (stat+sys), respectively, after one year of data taking. The corresponding expected fit precision of a sole experiment is evaluated at 8.7% and 10.1%, respectively. We also demonstrate the sensitivity towards fitting individual Th and U contributions, with best fit values of NTh=40-22+26 (stat+sys) and NU=180-24+30 (stat+sys). Finally, from the fit results of individual Th and U contributions, we evaluate the mantle signal to be Smantle=9.3±[5.2,5.4] NIU (stat+sys). This was obtained assuming a full-range positive correlation (ρc∈[0,1]) between Th and U, and the projected uncertainties on the crust contributions of 8.3% (Th) and 7.0% (U).

We present the sensitivity of the Theia experiment to low-energy geo- and reactor antineutrinos. For this study, we consider one of the possible proposed designs, a 17.8-ktonne fiducial volume Theia-25 detector filled with water-based liquid scintillator placed at Sanford Underground Research Facility (SURF). We demonstrate Theia's sensitivity to measure the geo- and reactor antineutrinos via Inverse-Beta Decay interactions after one year of data taking with \\(11.9\\times10^{32}\\) free target protons. The expected number of detected geo- and reactor antineutrinos is \\(218\\,^{+28}_{-20}\\) and \\(170\\,^{+24}_{-20}\\), respectively. The precision of the fitting procedure has been evaluated to be 6.72% and 8.55% for geo- and reactor antineutrinos, respectively. We also demonstrate the sensitivity towards fitting individual Th and U contributions, with best fit values of \\(N_\\text{Th}=39\\,^{+18}_{-15}\\) and \\(N_\\text{U}=180\\,^{+26}_{-22}\\). We obtain \\((\\text{Th}/\\text{U})=4.3\\pm2.6\\) after one year of data taking, and within ten years, the relative precision of the (Th/U) mass ratio will be reduced to 15%. Finally, from the fit results of individual Th and U contributions, we evaluate the mantle signal to be \\(S_\\text{mantle} = 9.0\\,\\pm [4.2,4.5]\\)NIU. This was obtained assuming a full-range positive correlation (\\(\\rho_c\\in[0, 1]\\)) between Th and U, and the projected uncertainties on the crust contributions of 8.3% (Th) and 7.0% (U). When considering systematic uncertainties on the signal and background shape and fluxes, the mantle signal becomes \\(S_\\text{mantle} = 9.3\\,\\pm [5.2,5.4]\\)NIU.

Water-based liquid scintillators (WbLS) present an attractive target medium for large-scale detectors with the ability to enhance the separation of Cherenkov and scintillation signals from a single target. This work characterizes the scintillation properties of WbLS samples based on LAB/PPO liquid scintillator (LS). X-ray luminescence spectra, decay profiles, and relative light yields are measured for WbLS of varying LS concentration as well as for pure LS with a range of PPO concentrations up to 90 g/L. The scintillation properties of the WbLS are related to the precursor LAB/PPO: starting from 90 g/L PPO in LAB before synthesis, the resulting WbLS have spectroscopic properties that instead match 10 g/L PPO in LAB. This could indicate that the concentration of active PPO in the WbLS samples depends on their processing.

MiniCLEAN is a single-phase liquid argon dark matter experiment. During the initial cooling phase, impurities within the cold gas (\\(<\\)140 K) were monitored by measuring the scintillation light triplet lifetime, and ultimately a triplet lifetime of 3.480 \\(\\pm\\) 0.001 (stat.) \\(\\pm\\) 0.064 (sys.) \\(\\mu\\)s was obtained, indicating ultra-pure argon. This is the longest argon triplet time constant ever reported. The effect of quenching of separate components of the scintillation light is also investigated.

Large-scale optical neutrino and dark-matter detectors rely on large-area photomultiplier tubes (PMTs) for cost-effective light detection. The new R14688-100 8-inch PMT developed by Hamamatsu provides state-of-the-art timing resolution of around 1 ns (FWHM), which can help improve vertex reconstruction and enable Cherenkov and scintillation light separation in scintillation-based detectors. This PMT also provides excellent charge resolution, allowing for precision photoelectron counting and improved energy reconstruction. The Eos experiment is the first large-scale optical detector to utilize these PMTs. In this manuscript we present a characterization of the R14688-100 single photoelectron response, such as the transit-time spreads, the dark-rates, and the afterpulsing. The single photoelectron response measurements are performed for the 206 PMTs that will be used in Eos.

We present measurements of the angular distribution of re-emitted light from tetraphenyl butadiene thin films when exposed to \\SI{128}{nm} light in vacuum. Films ranging from \\SI{250}{nm} to \\SI{5.5}{\\micron} in thickness are measured. All films were fabricated by evaporation deposition on ultraviolet transmitting (UVT) acrylic substrates. Preliminary comparisons of the angular distribution to that produced by a detailed Monte Carlo model are also presented. The current shortcomings of the model are discussed and future plans briefly outlined.

This is the final report from the Snowmass 2021 Neutrino Frontier Topical Group on Neutrinos from Natural Sources. It covers a broad range of neutrino sources, from low-energy neutrinos from the early universe to ultra high-energy sources. We divide this report by source, and discuss the motivations for pursuing searches in each case, the current state of the field, and the prospects for future theoretical and experimental developments. We consider neutrinos produced in the early universe; solar neutrinos; geoneutrinos; supernova neutrinos, including the diffuse supernova neutrino background (DSNB); neutrinos produced in the atmosphere; and high-energy astrophysical neutrinos.

This topical report of the 2021 US Community Study on the Future of Particle Physics (Snowmass 2021) summarizes the underground facilities needs for upcoming and next generation neutrino experiments. The underground facilities needs are discussed in the context of two broad categories: accelerator neutrinos, in particular with respect to the Deep Underground Neutrino Experiment (DUNE); and non-accelerator neutrinos, focusing on neutrinos from natural sources and on searches for neutrinoless double-beta decay.