Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E19: Dark Matter with Xenon DetectorsLive
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Sponsoring Units: DPF Chair: Mary Bishai, Brookhaven National Lab |
Saturday, April 17, 2021 3:45PM - 3:57PM Live |
E19.00001: The XENON1T Excess and What XENONnT Can Say About It Evan Shockley XENON1T is a dual-phase xenon time projection chamber that operated deep underground at Italy's Gran Sasso National Laboratory from 2016 to 2018. Primarily designed to search for WIMP dark matter, XENON1T featured a ton-scale target mass, keV-scale energy threshold, and ultra low background rate that together allowed for world-leading sensitivity to a variety of rare-event processes. Interestingly, an excess of electronic recoil events was observed in XENON1T, disfavoring at $> 3\sigma$ the background-only hypothesis. The origin of the excess remains unknown; however, XENON1T's successor, XENONnT, featuring a larger target mass and further reduced background level, is now being commissioned and will be able to probe the parameter space of interest with improved sensitivity. This talk will summarize the XENON1T result, briefly discuss possible explanations for the excess, and then detail the power of XENONnT to the distinguish various hypotheses. [Preview Abstract] |
Saturday, April 17, 2021 3:57PM - 4:09PM Live |
E19.00002: Projected WIMP Sensitivity of XENONnT Jacques Pienaar The multi-tonne XENONnT detector is the next step in the evolution of the XENON project. The experiment, aimed at direct detection of WIMPs, utilizes 5.9t of instrumented liquid xenon. Using a detailed GEANT4 model of the detector and radioassay results from detector components, we project the expected material background in the detector. In conjunction with improvements in suppressing intrinsic backgrounds from electronic recoil sources this allows XENONnT to reduce this background to an expected level 1/6th that of its predecessor within a 4t fiducial volume. The addition of a neutron veto around the XENONnT cryostat allows for significant suppression of the overall neutron background as well. In this talk we present the work done to model the response of the detector to energy deposition in the LXe volume. We project the 20 ty sensitivity to spin-independent WIMP-nucleon interactions to reach a cross-section of $1.4\times10^{-48}\,\mathrm{cm}^2$ for a 50\,GeV/c$^2$ mass WIMP at 90\% confidence level, more than one order of magnitude beyond the current best limits. [Preview Abstract] |
Saturday, April 17, 2021 4:09PM - 4:21PM Live |
E19.00003: Signal and background models for low-energy physics in XENON1T Joseph Howlett The XENON collaboration has recently published results searching for nuclear recoils produced by solar $^8$B neutrinos in XENON1T data. In order to achieve meaningful sensitivity, we lower the threshold from 2.6 keV to 1.6 keV, only requiring two scintillation photons and four ionization electrons. This increases the expected signal by an order of magnitude, but requires a number of novel techniques to reduce the consequent increase in backgrounds by two orders of magnitude. This talk will outline these techniques and the production and validation of the signal and background models used to develop them. The approach in this work can be carried forward to next-generation experiments to achieve greater sensitivity to $^8$B neutrinos and low-mass dark matter. [Preview Abstract] |
Saturday, April 17, 2021 4:21PM - 4:33PM Live |
E19.00004: Inference and interpretation of the XENON1T low-energy nuclear recoil search Knut Dundas Moraa, Joseph Howlett, Zihao Xu, Tianyu Zhu The XENON1T experiment has recently published results lowering the energy threshold in order to perform a search for nuclear recoils produced by solar $^8$B neutrinos using a $0.6$ tonne-year exposure. This signal is expected to be an irreducible background for future, higher exposure dark matter searches. The expected discovery power was $20\%$, and no significant excess was observed after unblinding. The low number of expected signal events, and strong degeneracies between the neutrino flux and the uncertain liquid xenon charge and light yields were treated together to compute the discovery significance and confidence volumes, both for this result alone and in combination with external constraints. With the same external constraints, new upper limits were set on the dark matter-nucleus cross-section for dark matter masses reaching down to $3~\mathrm{GeV}/c^2$, as well as a model of non-standard neutrino interactions. This talk will present the inference procedure used to produce the final results in this analysis. [Preview Abstract] |
Saturday, April 17, 2021 4:33PM - 4:45PM Live |
E19.00005: Light dark matter search in XENON1T using single- and few-electron ionization-only signals Amanda Depoian The energy threshold of liquid xenon detectors is driven by the requirements of observing a scintillation signal as well as a large ionization signal. Observing both allows powerful background rejection but limits the sensitivity below O(10GeV). In the first search from XENON1T for light dark matter, events using only the ionization signal were used to set limits down to WIMP masses of 3 GeV but was limited to an ionization signal of 5 electrons due to single- and few-electron backgrounds that were not well understood. A dedicated analysis was performed to understand these backgrounds and event selections were developed to mitigate them. In this talk, we discuss details of the analysis and present its status in a search for light dark matter signals using only the single- and few-electron ionization signals in the XENON1T detector and discuss the implications they have for XENONnT and supernova neutrino detection. [Preview Abstract] |
Saturday, April 17, 2021 4:45PM - 4:57PM Live |
E19.00006: Enhancement of waveform simulation for low-energy physics in XENON1T Tianyu Zhu The full simulation of signals in the XENON1T dark matter detector is made up of Geant4, models for scintillation light yields and ionization yields, and a so-called waveform simulation. This last step is a comprehensive model of the detector response, including position-dependent effects, photomultiplier responses and the pulse shapes created by scintillation and ionization signals. The simulation uses both external measurements and empirical data from XENON1T analyses, and its output may be passed directly to the data processing software used for real data. In a recent search for nuclear recoils produced by solar $^8$B neutrinos in XENON1T data, extending and validating the waveform simulator played a central part in computing the signal efficiency of the neutrino signal or low-mass dark matter. The enhancements we present address the mismatch between previous simulations and data, improving the simulation for the low-energy response. [Preview Abstract] |
Saturday, April 17, 2021 4:57PM - 5:09PM Live |
E19.00007: Improved electronic-recoil modeling in Xenon detectors with NEST Sophia Andaloro Noble-element detectors are broadly employed in rare-event nuclear and particle physics searches. The physics reach of these experiments requires accurate background and signal models. To this end, we developed the Noble Element Simulation Technique (NEST): a comprehensive, semi-empirical package for end-to-end simulation of noble element detector response. NEST simulates fundamental quantities, such as the scintillation and ionization yields of various particle interactions with noble elements, as well as detector-specific responses, such as the detector’s energy resolution and other observables. Recent upgrades to NEST, and to its Python equivalent, nestpy, have increased its flexibility when integrated into an experiment-specific code, and NEST’s options to simulate detector sensitivities enhance its applications from a phenomenological perspective. Most importantly for Xenon-based detector experiments is the recently-improved electronic recoil (ER) model within NEST, critical for calibration and background modeling. I will highlight NEST’s ER model, which we have expanded empirically to account for more unique ER-type particle interactions. The plans to finalize NEST for present and future generations of Xenon-based experiments will also be discussed. [Preview Abstract] |
Saturday, April 17, 2021 5:09PM - 5:21PM Live |
E19.00008: LIXO2: an upgraded system to study reflectivity of materials and PDE of SiPMs in liquid xenon. Alysse Hoelmer Next generation dark matter and neutrinoless double-beta decay experiments, e.g. nEXO and DARWIN, will use multi-ton liquid xenon (LXe) detectors. LXe emits vacuum ultraviolet (VUV) light. Little is known about reflective properties of materials and photon detectors, like Silicon Photomultipliers (SiPMs), in the VUV, which complicates optimization of these experiments. LIXO is a setup built at the University of Alabama to measure reflectivity of materials and photon detection efficiency (PDE) of SiPMs in LXe. LIXO has provided, for the first time, data on angular dependence of PDE and reflectivity of Hamamatsu SiPMs in LXe. This information is used by nEXO and DARWIN to understand light collection in their detectors. A downside of LIXO is that it takes long to measure a sample because one cannot change angle of incidence while in LXe. This talk describes the solution that will allow changing angular positions of the light source and detector in LXe, while still satisfying the stringent constraints due to the high-purity, cold environment. The upgraded system, LIXO2, will allow faster measurements with smaller systematics, wider angular range, and the ability to measure transparency of thin samples. Details of the design choices and the prototyping process is also presented. [Preview Abstract] |
Saturday, April 17, 2021 5:21PM - 5:33PM Live |
E19.00009: Optical simulation for DARWIN on GPUs with Chroma Luke Jones DARWIN is an ultimate dark matter detector that will utilize 50 tons of liquid xenon to search for dark matter. Due to its technological advantages, it will also be able to perform sensitive searches for other processes and particles, such as neutrinoless double-beta decay and axions. Optimizing the detector design and maximizing light collection in such a large, complex detector requires extensive optical simulations. This talk will describe the DARWIN optical simulation based on Chroma framework that was developed at the University of Alabama. Chroma uses GPUs for ultra-fast photon tracking and allows one to quickly investigate different design variants by directly using CAD files to describe detector geometry. Several studies that were conducted with the framework will be described. Comparison with the conventional, Geant4-based, simulation will also be presented. [Preview Abstract] |
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