Solar Axions Research Articles

A comprehensive calculation of the Primakoff process andthe solar axion flux

The Primakoff process plays a crucial role in axion productionin astrophysical environments and laboratories. Given the rising interestin axion physics and many on-going experimental activities, we conducta comprehensive calculation of this process and carefully examineseveral aspects that have been neglected in the literature. In particular,our calculation is valid for axions with significantly large masses,which would be of importance to axion searches utilizing crystal andliquid xenon detectors. We present the most updated calculation ofthe Primakoff solar axion flux, with a simple parametrization thatis applicable to a broad range of axion masses up to a few tens ofkeV. Our code is publicly available at GitHub.

Dynamic solar Primakoff process

The Primakoff mechanism is one of the primary channels for the production of solar axions. In canonical estimations of the Primakoff photon-axion conversion rate, the recoil effect is neglected and a static structure factor in adopted. By use of linear response theory, we provide a dynamic description of the solar Primakoff process. It is found that the collective electrons overtake ions as the dominant factor, in contrast to the static screening picture, where ions contribute more to the photon-axion conversion. Nonetheless, the resulting axion flux is only 1% to 2% lower than the standard estimate based on the static structure factor. Published by the American Physical Society 2024

Bragg-Primakoff axion photoconversion in crystal detectors

Axions and axion-like pseudoscalar particles with dimension-5 couplings to photons exhibit coherent Primakoff scattering with ordered crystals at keV energy scales, making for a natural detection technique in searches for solar axions. We find that there are large suppressive corrections, potentially greater than a factor of O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(103), to the coherent enhancement when taking into account absorption of the final state photon. This effect has already been accounted for in light-shining-through-wall experiments through the language of Darwin classical diffraction, but is missing from the literature in the context of solar axion searches that use a matrix element approach. We extend the treatment of the event rate with a heuristic description of absorption effects to bridge the gap between these two languages. Furthermore, we explore the Borrmann effect of anomalous absorption in lifting some of the event rate suppression by increasing the coherence length of the conversion. We study this phenomenon in Ge, NaI, and CsI crystal experiments and its impact on the projected sensitivities of SuperCDMS, LEGEND, and SABRE to the solar axion parameter space. Lastly, we comment on the reach of multi-tonne scale crystal detectors and strategies to maximize the discovery potential of experimental efforts in this vein.

OSIRIS-REx constraints on local dark matter and cosmic neutrino profiles

We derive purely gravitational constraints on dark matter and cosmic neutrino profiles in the solar system using asteroid (101955) Bennu. We focus on Bennu because of its extensive tracking data and high-fidelity trajectory modeling resulting from the OSIRIS-REx mission. We find that the local density of dark matter is bound by ρ DM ≲ 3.3 × 10-15 kg/m3 ≃ 6 × 106 ρ̅DM, in the vicinity of ∼ 1.1 au (where ρ̅DM ≃ 0.3 GeV/cm3). We show that high-precision tracking data of solar system objects can constrain cosmic neutrino overdensities relative to the Standard Model prediction n̅ν, at the level of η ≡ n ν/n̅ν ≲ 1.7 × 1011(0.1 eV/mν ) (Saturn), comparable to the existing bounds from KATRIN and other previous laboratory experiments (with mν the neutrino mass). These local bounds have interesting implications for existing and future direct-detection experiments. Our constraints apply to all dark matter candidates but are particularly meaningful for scenarios including solar halos, stellar basins, and axion miniclusters, which predict overdensities in the solar system. Furthermore, introducing a DM-SM long-range fifth force with a strength α̃D times stronger than gravity, Bennu can set a constraint on ρ DM ≲ ρ̅DM(6 × 106/α̃D). These constraints can be improved in the future as the accuracy of tracking data improves, observational arcs increase, and more missions visit asteroids.

Search for 8.4-keV Solar Axions Emitted in the M1 Transition in 169Tm Nuclei

Axions with an energy of 8.4 keV emitted in the М1 transition in 169Tm nuclei in the Sun are sought in the A + {{;}^{{169}}}{kern 1pt} {text{Tm}} → 169Tm* → ^{{169}}{text{Tm}} + (gamma ,e) (8.4 keV) reaction of resonant absorption by 169Tm nuclei on the Earth using a {text{T}}{{{text{m}}}_{{text{3}}}}{text{A}}{{{text{l}}}_{{text{5}}}}{{{text{O}}}_{{{text{12}}}}} thulium garnet crystal as a bolometric detector. The flux of monochromatic 8.4‑keV axions has been calculated. New constraints on the axion–nucleon coupling constants have been obtained and, as a result, new upper bounds on the axion mass m_{A}^{{{text{KSVZ}}}} leqslant {text{141}} eV and m_{A}^{{{text{DFSZ}}}} leqslant {text{244}} eV have been obtained at 90% C.L. in the KSVZ and DFSZ models, respectively.

Fabrication of a 64-Pixel TES Microcalorimeter Array With Iron Absorbers Uniquely Designed for 14.4-keV Solar Axion Search

If a hypothetical elementary particle called an axion exists, to solve the strong CP problem, a 57Fe nucleus in the solar core could emit a 14.4-keV monochromatic axion through the M1 transition. If such axions are once more transformed into photons by a 57Fe absorber, a transition edge sensor (TES) X-ray microcalorimeter should be able to detect them efficiently. We have designed and fabricated a dedicated 64-pixel TES array with iron absorbers for the solar axion search. In order to decrease the effect of iron magnetization on spectroscopic performance, the iron absorber is placed next to the TES while maintaining a certain distance. A gold thermal transfer strap connects them. We have accomplished the electroplating of gold straps with high thermal conductivity. The residual resistivity ratio (RRR) was over 23, more than eight times higher than a previous evaporated strap. In addition, we successfully electroplated pure-iron films of more than a few micrometers in thickness for absorbers and a fabricated 64-pixel TES calorimeter structure.

Recent progresses on BSM and dark matter searches with CUORE

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric 0\nu\beta\beta0νββ experiment to reach the one-tonne mass scale. The detector, located underground at the Laboratori Nazionali del Gran Sasso in Italy, consists of 988 TeO_22 crystals arranged in a compact cylindrical structure of 19 towers, operating at a base temperature of about 10 mK. After beginning its first physics data run in 2017, CUORE has since collected the largest amount of data ever acquired with a solid state detector and provided the most sensitive measurement of 0\nu\beta\beta0νββ decay in ^{130}130Te ever conducted. The large exposure, sharp energy resolution, segmented structure and radio-pure environment make CUORE an ideal instrument for a wide array of searches for rare events and symmetry violations. New searches for low mass dark matter, solar axions, CPT and Lorenz violations, and refined measurements of the 2\nu\beta\beta2νββ spectrum in CUORE have the potential to provide new insight and constraints on extensions to the standard model complementary to other particle physics searches. In this contribution, the recent progress on BSM and dark matter searches in CUORE are discussed.

ISAI: Investigating Solar Axion by Iron-57

The existence of the axion is a unique solution for the strong CP problem, and the axion is one of the most promising candidates of the dark matter. Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented table-top experiment to confirm the solar axion scenario. Probing an X-ray emission from the nuclear transitions associated with the axion-nucleon coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV X-ray from the first excited state of ^{57}57Fe using a state-of-the-art pixelized silicon detector, dubbed XRPIX, under an extremely low-background environment. We highlight scientific objectives, experimental design and the latest status of ISAI.

Performance of TES X-Ray Microcalorimeters Designed for 14.4-keV Solar Axion Search

A ^{57}Fe nucleus in the solar core could emit a 14.4-keV monochromatic axion through the M1 transition if a hypothetical elementary particle, axion, exists to solve the strong CP problem. Transition edge sensor (TES) X-ray microcalorimeters can detect such axions very efficiently if they are again converted into photons by a ^{57}Fe absorber. We have designed and produced a dedicated TES array with ^{57}Fe absorbers for the solar axion search. The iron absorber is set next to the TES, keeping a certain distance to reduce the iron-magnetization effect on the spectroscopic performance. A gold thermal transfer strap connects them. A sample pixel irradiated from a ^{55}Fe source detected 698 pulses. In contrast to thermal simulations, we consider that the pulses include either events produced in an iron absorber or gold strap at a fraction dependent on the absorption rate of each material. Furthermore, photons deposited on the iron absorber are detected through the strap as intended. The identification of all events still needs to be completed. However, we successfully operated the TES with the unique design under iron magnetization for the first time.

Betelgeuse constraints on coupling between axionlike particles and electrons

Axionlike particles (ALPs) can be produced by thermal processes in a stellar interior, escape from the star and, if sufficiently light, be converted into photons in the external Galactic magnetic field. Such a process could produce a detectable hard x-ray excess in the direction of the star. In this scenario, a promising class of targets is the red supergiants, massive stars which are experiencing the late part of their evolution. We report on a search for ALP-induced x-ray emission from Betelgeuse, produced via the combined processes of bremsstrahlung, Compton and Primakoff. Using a 50 ks observation of Betelgeuse by the NuSTAR satellite telescope, we set 95% C.L. upper limits on the ALP-electron (${g}_{ae}$) and ALP-photon (${g}_{a\ensuremath{\gamma}}$) couplings. For masses ${m}_{a}\ensuremath{\le}(3.5--5.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$, we find ${g}_{a\ensuremath{\gamma}}\ifmmode\times\else\texttimes\fi{}{g}_{ae}<(0.4--2.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$ (depending on the stellar model and assuming a value of the regular Galactic magnetic field in the direction transverse to Betelgeuse of ${B}_{T}=1.4\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{G}$). This corresponds to ${g}_{ae}<(0.4--2.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ for ${g}_{a\ensuremath{\gamma}}>1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$. This analysis supercedes by over an order of magnitude the limit on ${g}_{ae}\ifmmode\times\else\texttimes\fi{}{g}_{a\ensuremath{\gamma}}$ placed by the CAST solar axion experiment and is among the strongest constraints on these couplings.

Probing high-energy solar axion flux with a large scintillation neutrino detector

We investigate the 5.49 MeV solar axions flux produced in the $p(d,\, ^{3}{\rm He})a$ reaction and analyze the potential to detect it with the forthcoming large underground neutrino oscillation experiment Jiangmen Underground Neutrino Observatory (JUNO). The JUNO detector could reveal axions through various processes such as Compton and inverse Primakoff conversion, as well as through their decay into two photons or electron-positron pairs inside the detector. We perform a detailed numerical analysis in order to forecast the sensitivity on different combinations of the axion-electron ($ g_{ae} $), axion-photon ($g_{a\gamma}$), and isovector axion-nucleon ($ g_{3aN} $) couplings, using the expected JUNO data for different benchmark values of axion mass in a model-independent way. We find that JUNO would improve by approximately one order of magnitude current bounds by Borexino and it has the best sensitivity among neutrino experiments.

The Principle and Detection Progress of Axion Dark Matter

Detection of the axion is a significant yet challenging discovery for particle physics and astrophysics. Based on information retrieval and interpretation of results, a summary of state-of-art detection methods could be achieved, and future progress and be predicted. Although the axion suffices for its properties of hidden nature and impact on gravity, which leads to the difficulty of detection. There are currently several candidates for the detection of axions: cavity microwave experiments, solar axion searches, and radio telescope searches. With progress on all of these detection methods, analysis can be performed to establish a foundation for further development in these detection methods. If current methods continue to become more efficient and new methods are continuously proposed, the axion’s detection can be hastened and proof or counter-proof would be established quicker. Overall, these results offer a guideline for further axion search and newer questions based on the axion in the near future.

Simulation of TES X-ray Microcalorimeters Designed for 14.4 keV Solar Axion Search

Simulation of TES X-ray Microcalorimeters Designed for 14.4 keV Solar Axion Search

Jupiter missions as probes of dark matter

Jupiter, the fascinating largest planet in the solar system, has been visited by nine spacecraft, which have collected a significant amount of data about Jovian properties. In this paper, we show that one type of the in situ measurements on the relativistic electron fluxes could be used to probe dark matter (DM) and dark mediator between the dark sector and our visible world. Jupiter, with its immense weight and cool core, could be an ideal capturer for DM with masses around the GeV scale. The captured DM particles could annihilate into long-lived dark mediators such as dark photons, which subsequently decay into electrons and positrons outside Jupiter. The charged particles, trapped by the Jovian magnetic field, have been measured in Jupiter missions such as the Galileo probe and the Juno orbiter. We use the data available to set upper bounds on the cross section of DM scattering off nucleons, σχn, for dark mediators with lifetime of order mathcal{O} (0.1–1) s. The results show that data from Jupiter missions already probe regions in the parameter space un- or under-explored by existing DM searches, e.g., constrain σχn of order (10−41–10−39) cm2 for 1 GeV DM dominantly annihilating into e+e− through dark mediators. This study serves as an example and an initial step to explore the full physics potential of the large planetary datasets from Jupiter missions. We also outline several other potential directions related to secondary products of electrons, positron signals and solar axions.

Performance of the Li6Eu(BO3)3 crystal as a scintillating bolometer for studies of rare processes

In this article we report on a detailed study of the internal radioactive and chemical contamination of the Li6Eu(BO3)3 scintillating crystal operated as a cryogenic scintillating bolometer over 359 h. The excellent discrimination power of the detector allows to distinguish effectively beta/gamma events from alpha events. Whilst a weak activity of daughter nuclides from U/Th chains at the level few mBq/kg was observed, this crystal was found to be significantly contaminated by 147Sm, an alpha-active nuclide, at the level of about 0.5 Bq/kg. The light yield for β/γ events was determined to be 7.4(6) keV/MeV. The light yield and quenching factor for alpha particles vary in the range of (0.5–1.2) keV/MeV and (0.07–0.17), respectively, due to energy dependence of the emitted scintillating light in the energy interval (2.0–7.0) MeV. The integral luminescence intensity of the Li6Eu(BO3)3 crystal increases by more than four times only at low temperatures, below 80 K. Therefore, the Li6Eu(BO3)3-based cryogenic scintillating bolometers can be attractive detectors for direct neutron flux monitoring, to search for rare alpha decays or solar axions.

Search for New Physics in Electronic Recoil Data from XENONnT.

We report on a blinded analysis of low-energy electronic recoil data from the first science run of the XENONnT dark matter experiment. Novel subsystems and the increased 5.9ton liquid xenon target reduced the background in the (1, 30)keV search region to (15.8±1.3) events/(ton×year×keV), the lowest ever achieved in a dark matter detector and ∼5 times lower than in XENON1T. With an exposure of 1.16ton-years, we observe no excess above background and set stringent new limits on solar axions, an enhanced neutrino magnetic moment, and bosonic dark matter.

Search for Solar Axions via Axion-Photon Coupling with the Majorana Demonstrator.

Axions were originally proposed to explain the strong-CP problem in QCD. Through axion-photon coupling, the Sun could be a major source of axions, which could be measured in solid state detection experiments with enhancements due to coherent Primakoff-Bragg scattering. The Majorana Demonstrator experiment has searched for solar axions with a set of ^{76}Ge-enriched high purity germanium detectors using a 33kg-yr exposure collected between January, 2017 and November, 2019. A temporal-energy analysis gives a new limit on the axion-photon coupling as g_{aγ}<1.45×10^{-9} GeV^{-1} (95% confidence level) for axions with mass up to 100 eV/c^{2}. This improves laboratory-based limits between about 1 eV/c^{2} and 100 eV/c^{2}.

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

The resonant excitation of the 83Kr first excited nuclear level (E = 9.4 keV) by solar axions whose fluxes depend on the axion–electron coupling constant gAe is sought. The γ- and X-ray photons and the conversion and Auger electrons from the excited-level relaxation are detected with a gas proportional counter of a low-background detector in the underground Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences). As a result, a new constraint {text{|}}{{g}_{{Ae}}}(g_{{AN}}^{3} - g_{{AN}}^{0}){text{|}} ≤ 1.50 × 10–17 (90% C.L.) has been obtained for the axion–electron and axion–nucleon coupling constants, which corresponds to new constraints on the axion mass mA ≤ 320 eV and mA ≤ 4.6 eV in the KSVZ and DFSZ axion models, respectively.

Calculated Event Rates for Axion Detection via Atomic and Nuclear Processes

The possibility of detection of 5.5 MeV and 14.4 keV solar axions by observing axion-induced nuclear and atomic transitions is investigated. The presence of nuclear transitions between spin orbit partners can be manifested by the subsequent deexcitation via gamma ray emissions. The transition rates can also be studied in the context of radiative axion absorption by a nucleus. The elementary interaction is obtained in the context of the axion-quark couplings predicted by existing axion models. Then, these couplings will be transformed to the nucleon level utilizing reasonable existing models, which lead to effective transition operators. Using these operators, we calculate the needed nuclear matrix elements employing wave functions obtained in the context of the nuclear shell model. With these ingredients, we discuss possibilities of experimental observation of the axion-induced nuclear gamma rays. In the second part, we will examine the axion-induced production of X-rays (axion-photon conversion) or ionization from deeply bound electron orbits. In this case, the axion electron coupling is predicted by existing axion models; no renormalization is needed. The experimental signal is the observation of directly produced electrons and/or the emission of hard X-rays and Auger electrons, following the deexcitation of the final atom. Critical discussion is made on the experimental feasibility of detecting the solar axions by using multiton scale NaI detectors.

Probing the axion\u2013nucleon coupling with the next generation of\xa0axion helioscopes

A finite axion–nucleon coupling, nearly unavoidable for QCD axions, leads to the production of axions via the thermal excitation and subsequent de-excitation of ^{57}Fe isotopes in the sun. We revise the solar bound on this flux adopting the up to date emission rate, and investigate the sensitivity of the proposed International Axion Observatory IAXO and its intermediate stage BabyIAXO to detect these axions. We compare different realistic experimental options and discuss the model dependence of the signal. Already BabyIAXO has sensitivity far beyond previous solar axion searches via the nucleon coupling and IAXO can improve on this by more than an order of magnitude.