Session D14: Axion Dark Matter Search

Results of a Search for Axion-Like Particles using the Yale Microwave Cavity Experiment

Light neutral bosons with couplings to two photons are allowed in several extensions to the widely accepted Standard Model. We present results from a search for such axion-like particles (ALPs) using a cylindrical Cu resonant cavity in a 7 T axial magnetic field. The present experiment is sensitive (g$>$10$^{-7}$/GeV) to couplings between a scalar 10$^{-4}$ eV ALP and two microwave photons. We will discuss the existing measurements as well as modifications that are planned for detection of pseudoscalar ALPs.   

Searches for Structured Axion Dark Matter with ADMX

Axions are a compelling cold dark matter candidate. The Axion Dark Matter eXperiment (ADMX) searches for the Milky Way's halo of axions by their conversion into microwave photons in a resonant cavity threaded with a strong magnetic field. The detector has high spectral resolution, which allows for detection of narrow structures. We present preliminary results of searches for late infall axion lines, virialized axions, and sub-virialized axions.   

Improvements to the Axion Dark Matter eXperiment High Resolution Axion Search

The Axion Dark Matter eXperiment (ADMX) High Resolution (HR) Channel searches for flows of non-thermalized halo axions, characterized by their very low velocity dispersion, via the inverse Primakoff Effect. A power spectrum would show such axion flows as a peak with spectral broadening of order Hz or lower. The HR Channel is sensitive to signals of this nature, having a spectral resolution as fine as 40 mHz. In this talk we present a means of analysis for the HR data which will improve upon ADMX's recently published results (resolution of 10.8 Hz) by performing several searches using a range of resolutions while still accounting for signal modulation due to terrestrial motion.   

ADMX Phase II: Progress and Expected Sensitivity

The Axion Dark Matter eXperiment (ADMX) was recently moved to the University of Washington and is being rebuilt and upgraded. The centerpiece of the upgrades is the addition of a dilution refrigerator that will eliminate 95{\%} of the previous system's noise, greatly increasing sensitivity and range to detect dark matter axions. The status of current and planned upgrades will be discussed along with anticipated sensitivity estimates.   

High-Frequency Resonant Cavities for the Detection of Axion Dark Matter

The axion is a plausible dark matter candidate. The Axion Dark Matter eXperiment (ADMX) has conducted axion searches in the mass range of 1.9 -- 3.5 $\mu $eV (460 -- 850 MHz). Next-generation cavity designs will enable the exploration of a significantly larger portion of the favored dark matter axion mass-coupling phase space. ADMX is researching higher resonant frequency cavity designs, with Q-factor and effective volume comparable to or greater than the current experiment. Current concepts include segmented resonators, tunable periodic arrays, and superconducting hybrid cavities. The segmented resonator divides the cavity into equal volume sections, and combines the power (in phase) of each section. The tunable periodic arrays can be manipulated within the cavity to vary the resonance modes at high frequencies. Superconducting hybrids will use thin-film superconducting walls to obtain significantly higher Q-factors. Recent advances and future plans for cavity research will be presented.   

Searching for Dark Matter Axions beyond ADMX Phase II

The next-generation Axion Dark Matter Experiment (ADMX) is currently under construction and will have sensitivity to even pessimistic axion-photon couplings for dark matter axions with masses $<8\;\mu$eV (or $m_a c^2 < 2$ GHz). In order to extend the detection range to higher masses (8--100 $\mu$eV) new technologies must be developed. Here I will discuss the required detector research including development of higher frequency cavity and amplifier systems that can operate near the quantum limit in the 2--25 GHz region, thus allowing for a definitive dark matter axion search at these masses.   

Recent Developments in the SuperCDMS Experiment

Recent research and development in the SuperCDMS collaboration have resulted in the design of advanced dark matter detectors, called iZIPs, that should provide greatly improved results compared to the CDMSII experiment. Preliminary studies of iZIPs in above ground laboratories have demonstrated very efficient surface-event rejection and much improved phonon channel information on an event by event basis. Details of how the iZIP functions will be presented with a focus on results from preliminary studies. SuperCDMS is currently operating 15 iZIP detectors in the Soudan underground laboratory. Our aim is to better constrain the cross-section limits for dark matter, while proving the true capabilities of the iZIP technology. Preliminary information on the detector performance will be mentioned.   

Low background experimental characterization of space charge in IZIP detectors

The Cryogenic Dark Matter Search collaboration (CDMS) uses germanium crystals patterned with ionization electrodes and transition edge sensors to provide event by event discrimination for direct detection of cold dark matter. Recent improvements in detector design have introduced Interleaved ionization electrode geometries that offer the possibility of efficient rejection of near-surface events. We have implemented this interleaved approach for the charge and phonon readout for our germanium detectors. These detectors lose ionization stabilty more quickly than expected in both low background and surface test facility environments. The current science run in the Soudan underground lab consists of 15 detectors (10 kg). We present results of the initial commissioning datasets in comparison with surface test facilities and discuss methods implemented to maintain ionization stability.   

Ionization Measurements of 100~mm Diameter CDMS Ge Detectors

Future generations of Germanium-based dark matter search experiments aim to probe WIMP-nucleon cross-sections orders of magnitude smaller than the current best limits. The most feasible way of scaling the current Germanium detector technology to 100~kg or 1~ton scale includes increasing the size of individual detectors. The results of the ionization measurements of two 100~mm diameter and 33~mm thick Ge crystals, which are 2.3 times the volume of the current CDMS detectors, at $\sim$ 50~mK temperature are presented in this work. Some charge transport phenomena and the effects of evolving electric fields in detector-grade Germanium crystals at sub 100~mK temperatures are more pronounced in such larger crystals because of the larger dimensions. Together with the detector Monte Carlo simulations, this work deepens our understanding of the Germanium detector physics. The ionization performance of these devices with different charge electrode configurations demonstrates the potential of implementing such crystals in the next-generation 100~kg scale SuperCDMS experiment.