Solar Axions Research Articles

Solar axion search by annual modulation with XMASS-I detector

Kaluza-Klein (KK) axions produced in the Sun have been proposed to explain several astrophysical anomalies. We searched for the decay of such solar KK axions using 832 × 359 kg • days XMASS-I data. No significant event rate modulation is found, and we set the first experimental constraint on KK axion photon-coupling of 4.8 × 10“12 GeV−1 for a KK axion number density of (math) = 4.07 × 1013 m3 at 90% C.L.

International Axion Observatory (IAXO) status and prospects

International Axion Observatory (IAXO) is a new generation axion helioscope aiming to search for solar axions and axion-like particles (ALPs) with a signal to background ratio of about 5 orders of magnitude higher than the one achieved by currently the most sensitive axion helioscope, CAST. IAXO relies on large improvements in magnetic field volume and extensive use of X-ray focusing optics combined with low-background detectors. IAXO will probe a substantial unexplored region of the axion and ALP parameter space which is theoretically and cosmologically motivated, and thus will have significant discovery potential. IAXO could also be used to test models of other proposed particles at the low energy frontier of particle physics, like hidden photons or chameleons. In addition, the IAXO magnet could accommodate new equipment to search for relic axions or ALPs potentially composing the galactic halo of dark matter.

Development of TES Microcalorimeters with Solar-Axion Converter

Several issues in developing transition edge sensor (TES) microcalorimeters for the search of monochromatic solar axions expected at 14.4 keV are studied. The potential problem of developing TES’s of this purpose is in that an axion absorber of $$^{57}$$Fe must be placed in close vicinity of a TES. We estimated the minimum distance to avoid magnetic interference from iron using magnetic FEM simulations, and found it 30 $$\upmu $$m for an iron of 5 $$\upmu $$m thickness. We fabricated a TES with a 10 $$\upmu $$m thick iron membrane separated by 60 $$\upmu $$m. We confirmed the superconducting transition for this TES. However, both the residual normal resistance and the transition temperature was different from those of TES without iron. We also estimated the low-temperature thermal conductivity of an iron membrane by measuring the low-temperature electrical resistance and by applying the Wiedemann–Franz law. We estimated the pulse-shape dependency on the interaction position within the $$^{57}$$Fe converted using thermal FEM simulations. We found that the pulse-shape variations will limit the energy resolution to about 30 eV FWHM.

A test of bolometric properties of Tm-containing crystals as a perspective detector for a solar axion search

The $^{169}$Tm nuclide has first nuclear level at 8.41 keV with magnetic type transition to the ground state and, therefore, can be used as a target nucleus for the search of resonant absorption of solar axions. We plan to use a Tm-containing crystal of a garnet family Tm$_3$Al$_5$O$_{12}$ as a bolometric detector in order to search for the excitation of the first nuclear level of $^{169}$Tm via the resonant absorption of solar axions. With this perspective in mind, a sample of the Tm$_3$Al$_5$O$_{12}$ crystal was grown and tested for its bolometric and optical properties. Measurements of chemical and/or radioactive contaminations were performed as well. In this paper we present the test results and estimate the requirements for a future low-background experimental setup.

A search for solar axion induced signals with COSINE-100

We present results from a search for solar axions with the COSINE-100 experiment. We find no evidence of solar axion events from a data-set of 6,303.9 kg · days exposure and set a 90% confidence level upper limit on the axion-electron coupling, gae, of 1.70 ×10−11 for an axion mass less than 1 keV/c2. This limit excludes QCD axions heavier than 0.59 eV/c2 in the DFSZ model and 168.1 eV/c2 in the KSVZ model.

Physics potential of the International Axion Observatory (IAXO)

We review the physics potential of a next generation search for solar axions: the International Axion Observatory (IAXO) . Endowed with a sensitivity to discover axion-like particles (ALPs) with a coupling to photons as small as gaγ∼ 10−12 GeV−1, or to electrons gae∼10−13, IAXO has the potential to find the QCD axion in the 1 meV∼1 eV mass range where it solves the strong CP problem, can account for the cold dark matter of the Universe and be responsible for the anomalous cooling observed in a number of stellar systems. At the same time, IAXO will have enough sensitivity to detect lower mass axions invoked to explain: 1) the origin of the anomalous “transparency” of the Universe to gamma-rays, 2) the observed soft X-ray excess from galaxy clusters or 3) some inflationary models. In addition, we review string theory axions with parameters accessible by IAXO and discuss their potential role in cosmology as Dark Matter and Dark Radiation as well as their connections to the above mentioned conundrums.

Weighing the solar axion

Axion helioscopes search for solar axions and axion-like particles via inverse Primakoff conversion in strong laboratory magnets pointed at the Sun. While helioscopes can always measure the axion coupling to photons, the conversion signal is independent of the mass for axions lighter than around 0.02 eV. Masses above this value on the other hand have suppressed signals due to axion-photon oscillations which destroy the coherence of the conversion along the magnet. However, the spectral oscillations present in the axion conversion signal between these two regimes are highly dependent on the axion mass. We show that these oscillations are observable given realistic energy resolutions and can be used to determine the axion mass to within percent level accuracies. Using projections for the upcoming helioscope IAXO, we demonstrate that $>3\sigma$ sensitivity to a non-zero axion mass is possible between $3 \times 10^{-3}$ and $10^{-1}$ eV for both the Primakoff and axion-electron solar fluxes.

New mechanism producing axions in the AQN model and how the CAST can discover them

We advocate the idea that there is a fundamentally new mechanism for the axion production in the Sun, which has never been discussed previously in the literature. This novel mechanism of the axion production is based on the so-called Axion Quark Nugget (AQN) Dark Matter Model. These axions will be produced in addition to well studied axions emitted due to the Primakoff effect. The AQN model was originally invented as a natural explanation of the observed ratio $\Omega_{\rm dark} \sim \Omega_{\rm visible}$ when the DM and visible matter densities assume the same order of magnitude values, irrespectively to the axion mass $m_a$ or initial misalignment angle $\theta_0$. This model, without adjustment of any parameters, reproduces reasonably the intensity of the extreme UV (EUV) radiation from the solar corona as a result of the AQN annihilation events with the solar material. This extra energy released in corona represents a resolution, within AQN framework, a long standing puzzle known in the literature as the "solar corona heating mystery". The same annihilation events also produce the relativistic axions. This represents a new mechanism of the axion production, and constitutes the main subject of this work. The flux of these axions is unambiguously fixed in this model and expressed in terms of the EUV luminosity from corona. We also compute the spectral properties of these axions and make few comments on the potentials for the discovery of these solar axions by the upgraded CAST (CERN Axion Solar Axion) experiment.

Studies of radioactive background in SOI pixel detector for solar axion search experiment

An application of a modern noble pixel detector, XRPIX series, for solar KSVZ axion search experiment is being developed. A low radioactive background is necessary in the detector volume for the axion search. We surveyed the radioactivity of all peripheral components mounted on the detector using an HPGe detector. The results are used as an input for a GEANT4 Monte Carlo simulation to study the background in the experiment. This paper describes the expected background and the simulated sensitivity of stacked XRPIX detector currently under development.

Results of Searching for Solar Hadronic Axions Emitted in the M1 Transition in 83Kr Nuclei

Axions with the energy of $$9.4$$ keV emitted in the М1 transition in 83Kr nuclei in the Sun have been searched for using the resonant absorption reaction $$A + \,{{\,}^{{83}}}{\kern 1pt} {\text{Kr}} \to \,{{\,}^{{83}}}{\text{K}}{{{\text{r}}}^{ \star }} \to \,{{\,}^{{83}}}{\kern 1pt} {\text{Kr}} + \gamma ,e$$ (9.4 keV). A krypton-filled proportional counter located in a low-background setup is used to detect $$\gamma $$ rays and electrons. A new limit on the axion–nucleon coupling constant $$\left| {g_{{AN}}^{3} - g_{{AN}}^{0}} \right| \leqslant 8.4 \times {{10}^{{ - 7}}}$$ is obtained. In the hadronic axion model, it leads to a new limit on the axion mass $${{m}_{A}} \leqslant 65$$ eV (95% CL). A possibility of searching for solar axions with 57Fe-containing semiconductor crystals is described.

New Constraints on the Axion–Photon Coupling Constant for Solar Axions

Resonance excitation of the 83Kr first nuclear level (E = 9.4 keV) by solar axions formed via the Primakoff mechanism is sought. The γ- and X-ray photons and the conversion and Auger electrons arising from the excited-level relaxation are detected with a gas proportional counter of a low-background detector in the underground Baksan Neutrino Observatory. The following experimental constraint is obtained for the product of the axion–photon coupling constant and the axion mass:|gAγ × mA| ≤ 6.3 × 10 -17 In the framework of the hadronic-axion model, this corresponds to a new axion-mass constraint of mA ≤ 12.7 eV at 95% C.L.

Sensitivity of proposed search for axion-induced magnetic field using optically pumped magnetometers

We investigate a search for the oscillating current induced by axion dark matter in an external magnetic field using optically pumped magnetometers (OPMs). This experiment is based upon the LC circuit axion detection concept of Sikivie, Sullivan, and Tanner. The modification of Maxwell's equations caused by the axion-photon coupling results in a minute oscillating magnetic field at the frequency equal to the axion mass in the presence of magnetic field. This induced magnetic field could be searched for using an LC circuit amplifier with an OPM, the most sensitive cryogen-free magnetic-field sensor, in a room temperature experiment, avoiding the need for a complicated and expensive cryogenic system. We discuss how an existing magnetic resonance imaging (MRI) experiment can be modified to search for axions in a previously unexplored part of the parameter space. Our existing detection setup, optimized for MRI, is already sensitive to an axion-photon coupling of $10^{-7}$ GeV$^{-1}$ for an axion mass near $3\times10^{-10}$ eV. While this is ruled out by limits from astrophysics and solar axion searches, we show that realistic modifications, and optimization of the experiment for axion detection, can set a new limit on the axion-photon coupling up to three orders of magnitude beyond the current best limit, for axion masses between $10^{-11}$ eV and $10^{-7}$ eV.ion masses between $10^{-11}$ eV and $10^{-7}$ eV.

The ALP miracle revisited

We revisit the ALP miracle scenario where the inflaton and dark matter are unified by a single axion-like particle (ALP). We first extend our previous analysis on the inflaton dynamics to identify the whole viable parameter space consistent with the CMB observation. Then, we evaluate the relic density of the ALP dark matter by incorporating uncertainties of the model-dependent couplings to the weak gauge bosons as well as the dissipation effect. The preferred ranges of the ALP mass and coupling to photons are found to be 0.01 ≲ mϕ ≲ 1 eV and {g}_{phi gamma gamma }=mathcal{O}left(1{0}^{-11}right) GeV−1, which slightly depend on these uncertainties. Interestingly, the preferred regions are within reach of future solar axion helioscope experiments, IAXO and TASTE, and laser-based stimulated photon-photon collider experiments. We also discuss possible extensions of the ALP miracle scenario by introducing interactions of the ALP with fermions.

Estimating the flux of the 14.4 keV solar axions

In this paper we present a calculation of the expected flux of the mono-energetic 14.4 keV solar axions emitted by the M1 type nuclear transition of 57Fe in the Sun. These axions can be detected, e.g., by inverse coherent Bragg-Primakoff conversion in single-crystal TeO2 bolometers. The ingredients of this calculation are i) the axion nucleon coupling, estimated in several popular axion models and ii)the nuclear spin matrix elements involving realistic shell model calculations with both proton and neutron excitations. For the benefit of the experiments we have also calculated the branching ratio involving axion and photon emission. We find the solar axion flux on Earth to be Φa = 0.703×109cm-2s-1 (107 GeV/fa)2 and the branching ratio of axion to photon for the same model to be: wa/wγ = 0.229×10-15 ≈ 2×10-16.

Recent Results from the Majorana Demonstrator

The MAJORANA Collaboration has completed construction and is now operating an array of high purity Ge detectors searching for neutrinoless double-beta decay ([Formula: see text]) in [Formula: see text]Ge. The array, known as the MAJORANA DEMONSTRATOR, is comprised of 44 kg of Ge detectors (30 kg enriched to 88% in [Formula: see text]Ge) installed in an ultra-low background compact shield at the Sanford Underground Research Facility in Lead, South Dakota. The primary goal of the DEMONSTRATOR is to establish a low-background design that can be scaled to a next-generation tonne-scale experiment. This work reports initial background levels in the [Formula: see text] region of interest. Also presented are recent physics results leveraging P-type point-contact detectors with sub-keV energy thresholds to search for physics beyond the Standard Model; first results from searches for bosonic dark matter, solar axions, Pauli exclusion principle violation, and electron decay have been published. Finally, this work discusses the proposed tonne-scale [Formula: see text]Ge [Formula: see text] LEGEND experiment.

Search for resonant absorption of solar axions emitted in M1-transitions in 83Kr nuclei: Second stage of the experiment

Axions with energies of 9.4 keV putatively produced in the Sun via an M1-transition in the 83Kr nucleus are searched for using the reaction of resonant absorption: A +83Kr →83Kr* →83Kr + γ, e (9.4 keV). The γ-quanta and electrons are detected with a proportional counter filled with krypton and placed in a low-background setup. A new upper limit on the axion–nucleon coupling constant is imposed: |g AN 3 g AN 0 |≤1.02 106. For the hadronic axion, this implies a new upper limit on the axion mass: m A ≤ 79eV at the 95% confidence level.

Low energy analysis techniques for CUORE

CUORE is a tonne-scale cryogenic detector operating at the Laboratori Nazionali del Gran Sasso (LNGS) that uses tellurium dioxide bolometers to search for neutrinoless double-beta decay of ^{130}Te. CUORE is also suitable to search for low energy rare events such as solar axions or WIMP scattering, thanks to its ultra-low background and large target mass. However, to conduct such sensitive searches requires improving the energy threshold to 10 keV. In this paper, we describe the analysis techniques developed for the low energy analysis of CUORE-like detectors, using the data acquired from November 2013 to March 2015 by CUORE-0, a single-tower prototype designed to validate the assembly procedure and new cleaning techniques of CUORE. We explain the energy threshold optimization, continuous monitoring of the trigger efficiency, data and event selection, and energy calibration at low energies in detail. We also present the low energy background spectrum of CUORE-0 below 60 , mathrm {keV}. Finally, we report the sensitivity of CUORE to WIMP annual modulation using the CUORE-0 energy threshold and background, as well as an estimate of the uncertainty on the nuclear quenching factor from nuclear recoils inCUORE-0.

Recent Results of Search for Solar Axions Using Resonant Absorption by 83Kr nuclei

A search for resonant absorption of the solar axion by 83Kr nuclei was performed using the proportional counter installed inside the low-background setup at the Baksan Neutrino Observatory. The obtained model independent upper limit on the combination of isoscalar and isovector axion-nucleon couplings |g3 − g0| ≤ 8.4 × 10−7 allowed us to set the new upper limit on the hadronic axion mass of mA ≤ 65 eV (95% C.L.) with the generally accepted values S=0.5 and z=0.56.

Solar neutrino flux at keV energies

We calculate the solar neutrino and antineutrino flux in the keV energy range. The dominant thermal source processes are photo production (γ e→ e νν̄), bremsstrahlung (e+Ze→ Ze+e+νν̄), plasmon decay (γ→νν̄), and νν̄ emission in free-bound and bound-bound transitions of partially ionized elements heavier than hydrogen and helium. These latter processes dominate in the energy range of a few keV and thus carry information about the solar metallicity. To calculate their rate we use libraries of monochromatic photon radiative opacities in analogy to a previous calculation of solar axion emission. Our overall flux spectrum and many details differ significantly from previous works. While this low-energy flux is not measurable with present-day technology, it could become a significant background for future direct searches for keV-mass sterile neutrino dark matter.

Limits on Axion Couplings from the First 80 Days of Data of the PandaX-II Experiment.

We report new searches for solar axions and galactic axionlike dark matter particles, using the first low-background data from the PandaX-II experiment at China Jinping Underground Laboratory, corresponding to a total exposure of about 2.7×10^{4} kg day. No solar axion or galactic axionlike dark matter particle candidate has been identified. The upper limit on the axion-electron coupling (g_{Ae}) from the solar flux is found to be about 4.35×10^{-12} in the mass range from 10^{-5} to 1 keV/c^{2} with 90%confidence level, similar to the recent LUX result. We also report a new best limit from the ^{57}Fe deexcitation. On the other hand, the upper limit from the galactic axions is on the order of 10^{-13} in the mass range from 1 to 10 keV/c^{2} with 90%confidence level, slightly improved compared with the LUX.