Session B13: Mini-Symposium: Detecting Neutral Particles with Low-energy Thresholds

Theory Overview of Coherent Neutrino-Nucleus Scattering and Implications for Physics Beyond the Standard Model

The study of coherent neutrino-nucleus scattering provides an opportunity for novel tests of the Standard Model, and therefore for explorations of physics beyond the Standard Model including the search for non-standard neutrino interactions and portals to hidden particle sectors. Additionally, coherent neutrino-nucleus scattering presents an interesting challenge as an irreducible background for upcoming low-threshold experiments searching for direct detection of dark matter from dark matter-nuclei scattering processes. In this talk I will overview theoretical aspects of coherent neutrino-nucleus scattering including its Standard Model prediction, its utility in probing physics beyond the Standard Model in upcoming experiments, and its implications for the ultimate reach of direct detection of dark matter.   

Search for Dark Matter with DEAP-3600

DEAP-3600 is a single-phase liquid argon detector, which searches for dark matter particle interactions with 1 tonne fiducial target mass (3.6 tonnes total) contained in an ultra-pure acrylic vessel viewed by 255 high quantum efficiency photomultiplier tubes. It is located 2 km underground at SNOLAB, in Sudbury, Ontario. Radioactive backgrounds are controlled through pulse-shape discrimination in case of electromagnetic backgrounds (demonstrated with a smaller 7-kg prototype DEAP-1) and with a combination of excellent radiopurity, shielding and fiducialization for neutron and alpha backgrounds. The target sensitivity to spin-independent scattering of Weakly Interacting Massive Particles (WIMPs) on nucleons is $10^{-46}$ cm$^2$ at 100 GeV/c$^2$. Commissioning of the DEAP-3600 detector is now complete and physics data taking is starting. This talk will present an overview and status of the project, including early results demonstrating the detector performance.   

Detector Technologies for the COHERENT Experiment

The COHERENT experiment aims to make a first detection of Coherent Elastic Neutrino-Nucleus Scattering (CEvNS), measure the N$^2$ dependence of its cross section, and search for new physics beyond the standard model using the few $\times$ 10 MeV neutrinos from the pion decay at rest ($\pi$DAR) source at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. A suite of four detector technologies will be deployed near the neutrino source at the SNS to meet these goals. The detectors must be low-threshold and low-background in order to detect the low-energy nuclear recoils that occur from the CEvNS process with the SNS beam neutrinos. A 14 kg CsI[Na] crystal detector has been running for the past year. A 185 kg NaI[Tl] crystal detector array was commissioned at the SNS in the Summer of 2016. Next to be commissioned at the SNS in the Fall of 2016 are a 35 kg single phase liquid argon detector and a high-purity germanium detector. The performance of these detectors with regards to the CEvNS process will be presented.   

Dark matter searches with PICO bubble chambers: An overview

The PICO collaboration uses bubble chambers to search for dark matter, with world-leading sensitivity to the direct-detection of WIMPs with spin-dependent couplings to protons. PICO currently operates a 2 liter (PICO-2L) and a 32 liter (PICO 60) bubble chamber at the SNOLAB deep underground laboratory, and is currently constructing a 40 liter demonstration device that is expected to eliminate an anomalous background that has previously proven significant for the scaling of the bubble chamber technique to a future ton-scale experiment (PICO-500). A discussion of the technology, recent progress, and future plans will be presented.   

Prospects for using coherent elastic neutrino-nucleus scattering to measure the nuclear neutron form factor

Coherent elastic neutrino-nucleus scattering is a potential probe of nuclear neutron form factors. We show that the neutron root-mean-square (RMS) radius can be measured with tonne-scale detectors of argon, germanium, or xenon. In addition, the fourth moment of the neutron distribution can be studied experimentally using this method. The impacts of both detector size and detector shape uncertainty on such a measurement were considered. The important limiting factor was found to be the detector shape uncertainty. In order to measure the neutron RMS radius to 5\%, comparable to current experimental uncertainties, the detector shape uncertainty needs to be known to 1\% or better.   

$^{\mathrm{37}}$Ar Calibration of the Large Underground Xenon Experiment

The LUX collaboration released its 332 live-day WIMP search result in June 2016. Besides WIMPs, there are several other rare particles to search for using two-phase xenon detectors, such as axion-like pseudoscalars, axions, and electrophilic dark matter. All of these proposed particles interact with xenon via electron recoils at low energy. Also, the neutrino magnetic moment can be searched for by examining the rates of neutrino-electron scattering at low energy. Therefore, understanding xenon's response in this low-energy regime is vitally important. $^{\mathrm{37}}$Ar is an ideal source for calibrating a detector at these low energies, because it decays via electron capture (EC) and releases x-rays at two energies: 2.8 keV due to EC from the K-shell and 0.27 keV due to EC from the L-shell. Additionally, $^{\mathrm{37}}$Ar can be used to precisely study recombination fluctuations at a specific energy in the WIMP region of interest. Recombination fluctuations limit electron recoil discrimination efficiency, so understanding how these fluctuations change with electric drift field is important to all LUX analysis. This talk will explain the motivation, creation, deployment, and results of the $^{\mathrm{37}}$Ar source in LUX over a wide range of drift fields.   

The study of the correlation between ($\alpha $, $\gamma )$ induced events with respect to Radon annual modulation.

We observed ($\alpha $, $\gamma )$ reaction that~generates high energy gammas in Soudan mine with a~12 liter liquid scintillation detector. With~a model established to describe the correlation between ($\alpha $, $\gamma )$ induced events with radon annual modulation, we demonstrate~that ($\alpha $, $\gamma )$ induced events are highly~correlated~with the radon modulation.~ These~($\alpha $, $\gamma )$~induced events can be potential background events for rare event physics.