Session B07: Mini-Symposium: Noble Liquid Detectors I

R&D for LAr + Xe + photosensitive dopants

LArTPCs are the technology of choice for current and future neutrino experiments. Expanding the reach of LArTPCs to below the 10 MeV range would substantially enhance the flagship analyses of experiments like DUNE, while potentially enabling the physics of solar neutrinos, dark matter searches, and neutrinoless double beta decay searches. I outline the pathway and progress on R&D for photosensitive dopants, whose introduction into the LAr active medium, has a potential to enable the detection of low energy signals in large LArTPCs. This R&D program will demonstrate the feasibility and impacts of introducing doped LAr into current and future neutrino detectors at the kTon scale.   

Development of RF Carpet for Ion Transport in Gases

Neutrinoless double beta decay (0νββ) is a hypothetical process which if detected would be the rarest decay process ever observed. In this process, two neutrons in a nucleus simultaneously beta decay without producing any antineutrinos. Its detection would prove the neutrino to be a Majorana fermion. The long half-life of this decay > 10²⁶ years require development of efficient background suppression and signal identification methodologies. The NEXT collaboration is searching for this decay using a gaseous xenon time projection chamber enriched in xenon-136, and employs topological reconstruction and excellent energy resolution (1% FWHM) to reduce background levels towards 1 count/year in the signal region. The use of xenon detectors also offer a further opportunity: the implementation of single barium daughter ion tagging, an approach that may reduce radiogenic and cosmogenic backgrounds by orders of magnitude and unlock sensitivities that extend beyond the inverted neutrino mass ordering. In such experiments, efficient capture and identification of single barium ions is crucial. In this talk I will present recent advances in the development of RF carpet for ion collection and extraction from a ton to multi-ton scale volume of high pressure gas.   

Electron Lifetime Measurements in the LUX-ZEPLIN (LZ) Dark Matter Experiment

The LZ experiment is a dual-phase liquid xenon Time Projection Chamber (TPC) located at the Sanford Underground Research Facility (SURF) to detect Weakly Interacting Massive Particles (WIMPs). Dual-phase TPCs are designed to observe interactions that either excite or ionize a medium via a prompt scintillation (S1) at the interaction site and a delayed amplified signal (S2) in the extraction region at the gas-liquid interface near the top of the detector. The prompt S1 signal is created by de-excitation and recombination of xenon atoms, while the delayed S2 signal is created after transporting the freed electrons from the interaction site to undergo electroluminescence in gaseous xenon via a strong electric field. Using the S1 and S2 signals, we can perform a three-dimensional reconstruction of an interaction. Calibrating and understanding how the detector response varies as a function of position and time is critical for event identification to distinguish background from signal. One aspect that can affect our S2 signal is electron lifetime, which reflects how many signal electrons are lost over time due to impurities in liquid xenon. Electron lifetime depends both on the purity of the medium and the strength of the drift electric field, both of which can vary over time and position in the TPC. This presentation will describe the results of LZ's electron lifetime analysis to understand the drift of electrons in the LZ detector, which plays a crucial role for event reconstruction.   

A study on the VUV reflectivity of detector materials for the nEXO experiment

nEXO is a tonne-scale experiment that will search for neutrinoless double beta decay of $^{136}\text{Xe}$ in an ultra-low background, single-phase liquid xenon (LXe) time projection chamber equipped with a readout of scintillation light. The projected sensitivity for the half-life of this decay is $>10^{28}$ years over 10 years of run time. Scintillation photons of 178 nm wavelength from interactions in the LXe will be collected by a large-array ($\sim$ 4.6 $\text{m}^2$ area ~\cite{precodr}) of VUV-sensitive silicon photomultipliers (SiPMs). To maximise the light collection efficiency, the detector materials need to be highly VUV reflective. This presentation reports the study of VUV optical properties of materials considered for the nEXO detector in an LXe test bench at UMass Amherst housing an FBK VUV HD3 SiPM ($\sim$ 1 $\text{cm}^2$), an $^{241}\text{Am}$ alpha source, and reflectors under test. A GPU-based ray tracing software called Chroma was used to simulate experimental configurations. In addition to the reflector's refractive index and the SiPM reflectivity in LXe, the photon transport efficiency (PTE) of the system depends on multiple parameters of the system, including the LXe refractive index, scintillation wavelength, and absorption and scattering lengths. Using the best estimates of these factors from literature \cite{lxe,lxescin,lxescatter}, simulated PTE values are compared to the measurements of the same configurations illuminated by alpha scintillation pulses. The estimates of the diffusivity and specularity of the reflectors along with their systematic errors are reported. Future work entails the construction of a multivariate matrix to span the broad parameter space and understand its correlations. This will ultimately become an important part of the scintillation event reconstruction algorithm in nEXO.