Session Z20: Probing the Dark Sector with Haloscopes & Other Techniques

Live

We introduce a new strategy to search for dark matter axions using tunable cryogenic plasmas. Unlike current experiments, which repair the mismatch between axion and photon masses by breaking translational invariance (cavity and dielectric haloscopes), a plasma haloscope enables resonant conversion by matching the axion mass to a plasma frequency. A key advantage is that the plasma frequency is unrelated to the physical size of the device, allowing large conversion volumes.   

Live

Dark photons (DPs) produced in the early Universe are well-motivated dark matter (DM) candidates. We show that the recently proposed tunable plasma haloscopes are particularly advantageous for DP searches. While in-medium effects suppress the DP signal in conventional searches, plasma haloscopes make use of metamaterials that enable resonant absorption of the DP by matching its mass to a tunable plasma frequency and thus enable efficient plasmon production. Using thermal field theory, we confirm the in-medium DP absorption rate within the detector. This scheme allows us to competitively explore a significant part of the DP DM parameter space in the DP mass range of $6-400$ $\mu$eV. If a signal is observed, the observation of a daily or annual modulation of the signal would be crucial to clearly identify the signal as due to DP DM and could shed light on the production mechanism.   

Live

Axions are a well-motivated class of dark matter models that also solve the strong CP problem in quantum chromodynamics. Currently there are many axion direct detection experiments probing different regions in parameter space, but the next generation of these experiments will feature multiple detectors operating at various terrestrial locations. Because of the wave-like nature of axion dark matter, the spatial separation of these experiments will allow measurements of the relative phase that is inaccessible to a single detector. In this talk, I will discuss the formalism to extract the signal from these experiments and illustrate how we can use these experiments to estimate parameters in the dark matter velocity distribution invisible to a single detector.   

Live

If dark matter is an ultralight axion-like particle, the gradient of its classical field can be detected in precision atomic experiments, including helium-potassium comagnetometers. In this talk, I will discuss a re-analysis of existing comagnetometer data with world-leading sensitivity to axions in the mass range from $10^{-17}$ to $10^{-12}$ eV that couple to neutrons. Proper interpretation of this data requires a careful treatment of the dark matter velocity distribution, which leads to stochastic fluctuations of the signal amplitude. I will introduce a complete statistical treatment for these stochastic effects, which has implications for any experiment that is sensitive to the gradient of the axion field.   

Live

Axions are a generic expectation in many extensions of the Standard Model. Neutron stars have long been a stringent probe of axions through observations of their cooling. Axions can be created within the hot core of the neutron star and escape the star due to their weak interactions with matter. However, the emitted axions can then be detected in X-ray observations if they convert into an X-ray photon on the way to Earth, for example in the magnetosphere of the star. Here I present a summary of recent works searching for evidence of these particles from X-ray observations of nearby neutron stars knonwn as the Magnificent Seven. In particular, I focus on the recent discovery of an X-ray excess from the Magnificent Seven. This excess is consistent with the axion-nucleon bremsstrahlung expectation for an axion with the product of photon and nucleon couplings $g_{a\gamma\gamma}\times g_{ann} \in (2 \times 10^{-21}, 10^{-18})$ GeV$^{-1}$ and mass $m_a < 2 \times 10^{-5}$ eV. Furthermore, I discuss a new axion production channel inside neutron stars via synchrotron emission off of neutrons and muons, and discuss the implications of this channel for the Magnificent Seven excess.   

Live

Detection and understanding of dark matter is one of the major unsolved problems of modern particle physics and cosmology. Several theories of fundamental physics predict bosonic dark matter candidates that can modify Maxwell’s equations resulting in additional photon emission from conducting surfaces. One of these promising dark matter candidates is known as the axion, which could be detected by observing the emitted electromagnetic radiation resulting from axion-photon coupling. The Broadband Reflector Experiment for Axion Detection (BREAD) haloscope experiment will investigate a currently underprobed dark matter parameter space using novel reflector technology. This new experiment will develop technology for a new type of wideband axion dark matter search experiment capable of detecting axions in the mass range of approximately 10 meV -- 30 eV, a range not currently accessible by other techniques. This target mass range corresponds to an observable dark matter signal in the under-probed terahertz regime. This presentation will cover the commissioning and building of a preliminary, room-temperature, terahertz photon source testing and calibration system that is intended to be used for a prototype BREAD detector.   

Live

We present current experiments being undertaken at the University of Western Australia to search for axions of mass below one micro electron volt. First we discuss a technique that detects the electromotive force generated in an electronic circuit when converting axions to electricity under a DC magnetic field [1-4]. The second technique mixes two frequency stabilized oscillators, which interact with the axion at the difference frequency of the oscillators [5]. Initial experiments put various limits on the axion-photon coupling, and we discuss the experimental path to search for known axion models. [1] ME Tobar, BT McAllister, M Goryachev, Phys. Rev. Applied 15, 014007 (2021) [2]ME Tobar, RY Chiao, M Goryachev, arXiv:2101.00945 [physics.class-ph], (2021) [3]ME Tobar, BT McAllister, M Goryachev, Physics of the Dark Universe26, 100339 (2019) [4]ME Tobar, BT McAllister, M Goryachev, Physics of the Dark Universe30, 100624 (2020) [5] CA Thomson, BT. McAllister, M Goryachev, EN Ivanov, ME Tobar, arXiv:1912.07751 [hep-ex]   

Live

A measurement of the transmission coefficient for neutrons through a thick ($\sim 3$\,atoms/b) liquid natural argon target in the energy range $30$-$70$\,keV was performed by the Argon Resonance Transmission Interaction Experiment (ARTIE) using a time of flight neutron beam at Los Alamos National Laboratory. In this energy range theory predicts an anti-resonance in the $^{40}$Ar cross section near $57$\,keV, but the existing data, coming from an experiment performed in the 90s (Winters. et al.), does not support this. This discrepancy gives rise to significant uncertainty in the penetration depth of neutrons through liquid argon, an important parameter for next generation neutrino and dark matter experiments. In this talk, the first results from the ARTIE experiment will be presented. The ARTIE measurement of the total cross section as a function of energy confirms the existence of the anti-resonance near $57$\,keV, but not as deep as the theory prediction.   

Live

Dark matter has traditionally been modeled as a single particle. However, the visible matter making up $\sim$15\% of the matter density of the universe is much more complex. Assuming that dark matter is similarly complex, there may exist an entire hidden sector of matter composed of multiple types of dark matter particles, with their own self-interactions. The canonical example of such an interaction would be a dark electromagnetic force mediated by a dark photon. This massive U(1) gauge boson would kinetically mix with Standard Model photons, which can then be measured by the standard haloscope used in axion searches. When taking the dark photon to comprise the majority of the hidden sector, deep exclusions can be made in the mass range that haloscopes are sensitive to, improving current limits by three orders of magnitude. I will present results for a search for dark photons with the HAYSTAC experiment in the mass regions of 16.96-17.12, 17.14-17.28, and 23.15-24.0 $\mu$eV.