Session DM: Mini-Symposium on Double Beta Decay and Dark Matter II

An Analysis of the LUX First WIMP Search Run Using Effective Field Theory Techniques

The LUX (Large Underground Xenon) experiment is a dark matter direct detection experiment located 4850 feet underground at the Sanford Underground Research Facility in Lead, SD. During Summer 2013, LUX collected 10065 kg-days of WIMP search data, ultimately reporting a minimum cross-section limit for spin-independent WIMP-nucleon elastic scattering of 7.6 $\times$ 10$^{-46}$ cm$^2$ for 33 GeV-mass WIMPs. Direct detection experiments typically characterize WIMP-nucleon interactions in terms of spin-independent (SI) and spin-dependent (SD) couplings. However, Fitzpatrick et al.\footnote{Fitzpatrick et al., JCAP 1302 (2013) 004 arXiv:1203.3542.} show that the total set of effective field theory operators allowed by basic symmetry considerations result in additional qualitatively distinct nuclear responses for WIMP-nucleon interactions. These new operators can also interfere with the standard SI and SD operators, potentially enhancing or suppressing them, and should therefore be taken into consideration to ensure that direct detection experiments do not leave any gaps in the theoretical parameter space being probed. Here I discuss recent work toward using the LUX 2013 WIMP search dataset to set limits on these new operators.   

Performance and Result from DarkDide-50

DarkSide-50 (DS-50) at Gran Sasso underground laboratory, Italy, is a direct dark matter search experiment based on a TPC with liquid argon from underground sources. The DS-50 TPC, with 50 kg of active argon and a projected fiducial mass of $>$33 kg, is installed inside an active neutron veto based on a boron-loaded organic scintillator. The neutron veto is built inside a water Cherenkov muon veto. DS-50 has been taking data since Nov 2013, collecting more than 20 M events with atmospheric argon. This data represents an exposure to the largest background, beta decays of Ar-39, comparable to the full three-year run planned for DS-50 with underground argon. When analyzed with a threshold that would give a sensitivity in the full run of about 1e-45 cm$^2$ at a WIMP mass of 100 GeV/c$^2$, there is no Ar-39 background observed in WIMP expected region. The detector design and performance will be presented as well as results from the atmospheric argon run still in progress. Plans for the underground argon run and for a ton-scale detector within the same neutron veto vessel will be presented.   

SuperCDMS-Soudan Low-Mass WIMP Constraints and the Next-Generation Detectors

SuperCDMS is the next generation of the Cryogenic Dark Matter Search. Approximately two years of data have already been taken at the Soudan Underground Laboratory (2090~m.w.e), and the collaboration is preparing for installation at SNOlab (6010~m.w.e). CDMS searches for dark matter via direct detection with silicon and germanium crystal targets at cryogenic temperatures ($\sim$50 mK). Two recent publications with especially impressive low-mass limits underscore the versatility of the SuperCDMS detectors and show how their technology is the basis for a multifaceted approach to dark matter direct detection. Of key importance for these and future results are precision data handling and incremental detector improvements. Here the processing and analysis techniques used for the maximum physics reach down to the lowest recoil energies possible are discussed. Specifically, we consider how the quality of the data processing algorithms and analysis techniques drove the science reach of the recent publications. Data from the next-generation detectors is also discussed, and the performance of these detectors is put into the context of future SuperCDMS-SNOlab results.   

DEAP-3600 Dark Matter Search at SNOLAB

The DEAP-3600 experiment will search for dark matter particle interactions on 3.6 tonnes of liquid argon at SNOLAB. The argon is contained in a large ultralow-background acrylic vessel viewed by 255 8-inch photomultiplier tubes. Very good pulse-shape discrimination has been demonstrated for scintillation in argon, and the detector has been designed for a total background budget, including (alpha,n) and external neutron recoils, surface contamination from 210Pb and radon daughters, of 0.2 events per tonne-year, allowing an ultimate sensitivity to spin-independent scattering of 10$^{-46}$ cm$^2$ per nucleon at 100 GeV mass. Installation of the detector is currently being completed at SNOLAB. The status of the experiment and an overview of low background techniques employed will be presented.   

KamLAND-PICO dark matter search project Low background test by highly radiopure NaI(Tl)

KamLAND-PICO aims to search for WIMPs dark matter by means of highly radiopure NaI(Tl) scintillator. The impurities in NaI(Tl) has been successfully reduced by chemical processing of raw NaI(Tl) powder. The intensity of alpha ray was observed and the contamination in 210Pb has been dramatically reduced to about 60 $\mu$Bq/kg. The present status of low background measurement will be reported.   

Dark photon search in Dalitz decays at PHENIX

The dark photon is a hypothetical gauge boson of an additional U(1) gauge field, which couples to dark matter but not to ordinary matter. The dark photon mixes with ordinary photons and may possibly explain some experimental results which have been interpreted as signatures of Beyond Standard Model physics. Recently a dark photon search has been made using high statistics data from the PHENIX experiment at RHIC. We search for events which can contain electron pairs from dark photon in $\pi^{0}$ and $\eta$ Dalitz decays. In this talk, we will report the latest status of the dark photon search at PHENIX.   

Recombination in liquid xenon for low-energy recoils

Detector response to low-energy recoils in sub-keV region is critical to detection of low-mass dark matter particles-WIMPS (Weakly interacting massive particles). The role of electron-ion recombination is important to the interpretation of the relation between ionization yield and scintillation yield, which are in general anti-correlated. Recent experimental results show that ionization yield increases down to keV range. This phenomenon contradicts general understanding for low energy recoils in the keV range in which direct excitation dominates. The explanation is that recombination becomes much less efficient when the track length is smaller than the thermalization distance of electrons. However, recombination rate is also proportional to ionization density, which is very high for keV recoils. To understand how recombination rate behaves for keV recoils, we calculated both initial recombination rate and volume recombination rate for keV recoils in liquid xenon. In this paper, we show the results of the calculated recombination rate as a function of recoil energy for both electronic recoils and nuclear recoils.   

Low Temperature CaMoO$_{4}$ Crystal Detectors for the AMoRE Project

The AMoRE (Advanced Mo-based Rare process Experiment) project is an international experiment to search for neutrinoless double beta decay of $^{100}$Mo. Excellent energy resolution and particle-type discrimination are essential to improve the experimental sensitivity in rare event search experiments of this type. Here we report performances of low temperature detectors composed of CaMoO$_{4}$ crystals and metallic magnetic calorimeters (MMCs). Both of heat (phonon) and light (photon) measurements were carried at tens of milli-Kelvin temperatures. The FWHM energy resolution was obtained to be 5-9 keV for environmental gamma ray peaks in the phonon channel. Clear separation (better than 15 $\sigma$) was found for alpha and electron events with heat/light ratio comparison. Pulse shape discrimination with phonon signal only was also successful with better than 15 $\sigma$ of discrimination power. Moreover, signal rise-time with the MMC sensors was faster than 1 ms. It may improve rejection ability for random coincidences of two neutrinos double beta decay events that is one of major background sources for the experiment.   

Development of enriched $^{130}$TeO$_{2}$ crystals for neutrinoless double beta decay searches

The Cryogenic Underground Observatory for Rare Events (CUORE) will search for the neutrinoless double-beta decay of $^{130}$Te using an array of 988 bolometers comprised of natural-isotopic-composition TeO$_{2}$. We are now investigating the feasibility of producing $^{130}$Te-enriched crystals for a possible future improved search of this kind. Together with the Shanghai Institute of Ceramics, we have developed a tentative crystal-production plan. Ten kilograms of 92{\%}-enriched $^{130}$Te metal are currently available for this project. In order to test possible effects on the crystal growth process, 500 grams of this material have been converted into TeO$_{2}$ and then blended with natural TeO$_{2}$ to produce three 5x5x5-cm$^{3}$ TeO$_{2}$ crystals with a 40{\%} $^{130}$Te abundance. These crystals have been tested as bolometers at the Gran Sasso National Laboratory. Preliminary results from this effort will be presented along with plans for further development of enriched crystals for neutrinoless double-beta decay searches.   

Design and performance of the Majorana low-noise low-background front-end electronics

The Majorana Demonstrator will search for the neutrinoless double beta decay ($\beta\beta$(0$\nu$)) of the isotope $^{76}$Ge. In view of the next generation of tonne-scale germanium-based $\beta\beta$(0$\nu$)-decay searches, a major goal of the Majorana Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039-keV Q-value of the $^{76}$Ge $\beta\beta$(0$\nu$)-decay. Such a requirement on the background level significantly constrains the design of the readout electronics which is further driven by noise performances. We present here the low-noise low-background front-end electronics developed for the low-capacitance P-type point-contact (PPC) germanium detectors of the Majorana Demonstrator. This resistive-feedback front-end, specifically designed to have low mass, is fabricated on a radioactivity-assayed fused silica substrate where the feedback resistor consists of a sputtered thin film of high purity amorphous germanium and the feedback capacitor is based on the capacitance between circuit Au traces. Performance studies of the front-end and associated back-end electronics in single and multi-detector systems, as well as on-site performances are reported.   

Assembly and design of the germanium detectors for the Majorana Demonstrator

The Majorana Demonstrator is a neutrino-less double-beta decay experiment being carried out at the Sanford Underground Research Facility, in South Dakota.~ The Demonstrator will consist of 30 kg of germanium detectors enriched in 76Ge. Each P-type Point Contact detector is arranged in a string configuration, utilizing novel front-end electronics, cables, connectors, and mounts,~ fabricated from radio-pure materials. The assembly of the strings is carried out 4850 feet underground to reduce cosmologically induced backgrounds. To further reduce backgrounds, strings are assembled in a nitrogen-filled glovebox. This talk will give an overview of the design and the assembly of the detector strings for the Majorana Demonstrator.~