arXiv subjects

Jaime Ruz

Publications and source records attributed to Jaime Ruz.

10 recordsLinked to original sources

arXiv2026

Overview and design optimization of a custom hybrid X-ray telescope for the International Axion Observatory (IAXO)

We present the design optimization for maximizing the effective area of a custom X-ray optic for the International Axion Observatory (IAXO) and BabyIAXO, including its novel hybrid configuration that enables full coverage of the 700-mm-diameter magnetic bore with minimal stress imposed on the mirrors; shell layout optimized for axion spectra and spatial distribution; and the coating recipes that enhance reflectivity in the energy range of interest. We evaluate how these design choices improve the observation signal-to-noise ratio (SNR) of BabyIAXO and IAXO by calculating the broad-band effective area and simulating the point spread function (PSF) and focal spot at the detector plane. The cost-effective and scalable optic offers an energy response from 0.03--15 keV, achieving an effective area that exceeds 2400 cm$^2$ near 1 keV - the peak of the ABC axion spectrum - and remains above 1700 cm$^2$ around 3 keV - the peak of the Primakoff axion spectrum. It yields a half-power diameter (HPD) of $\sim 46^{\prime\prime}$ for an on-axis point source at infinity, and a focal-spot HPD of $\sim 120^{\prime\prime}$ for the radial distribution expected for axion signals within the approximately $3^{\prime}$-radius solar core. A relatively generous fabrication-error budget is also summarized. The custom optic, accounting for fabrication errors, is anticipated to deliver a more than $55$-fold enhancement in the SNR.

physics.ins-det↗

arXiv2026

Fabrication status and expected performance of the inner-core X-ray optic for BabyIAXO

BabyIAXO, a pathfinder for the International Axion Observatory (IAXO), is designed to demonstrate all key technologies at scale while achieving an improvement in sensitivity over the recent CERN Axion Solar Telescope (CAST) experiment by approximately a factor of five. Such improvement is enabled by the X-ray optics, which allow for maintaining a high signal-to-noise ratio at the detector despite a cross-sectional area of the magnetic bore being over 250 times larger than that of CAST. The optic employs a hybrid design consisting of co-aligned inner core and outer corona optics that share a common optical axis and vacuum vessel but differ in focal length and manufacturing approach. Both are segmented glass optics, with the inner core fabricated from thermally slumped borosilicate glass and the outer corona from cold-slumped Corning Willow glass. To fabricate the inner-core optic, leveraging techniques developed for NuSTAR and HEFT optics, we reoptimized and streamlined the thermal-forming procedure. The quality of free-standing glass substrates was characterized by laser metrology, X-ray reflectometry, and atomic force microscopy. We developed a cutting technique that produces smooth edges at the micron scale. We used flat stacks of glass-epoxy-graphite layers to evaluate the performance of the epoxy bondline. The optic is expected to achieve an on-axis point spread function (PSF) with a half-power diameter (HPD) of < 90", enhancing the signal-to-noise ratio by more than 55 times.

physics.ins-det↗

arXiv2026

NuSTAR as an Axion Helioscope: probing axion-nucleon and axion-electron couplings

We investigate solar X-ray observations as a probe of axions and axion-like particles. These particles can be produced in the interior of the Sun via the conversion of thermal photons, as well as through processes involving axion-electron and axion-nucleon interactions. The resulting axions can then reconvert into photons in the Sun's atmospheric magnetic field, generating a signal in the X-ray energy range. In this work, we derive new limits on axions using X-ray observations with the Nuclear Spectroscopic Telescope Array (NuSTAR) during the 2020 solar minimum. In the regime where ALP production is dominated by couplings to electrons or nucleons, we obtain bounds on the product of couplings $g_{ae}\cdot g_{a\gamma}\lesssim 1.1\times10^{-24}\,\rm GeV^{-1}$ and $g_{aN}^{\rm eff}\cdot g_{a\gamma}\lesssim 2.3\times 10^{-19}\,\rm GeV^{-1}$ at 95% CL, for axion masses $m_a\lesssim10^{-6}\,\rm eV$. These constraints strongly improve current ground-based experimental limits, establishing solar X-ray observations as a powerful and robust method for axion searches.

astro-ph.CO↗

arXiv2026

Axions at the meV Crossroads: Theory, Cosmology, Astrophysics, and Experiments

The meV mass range has emerged as a focal point in axion physics, where advances in theory, cosmology, astrophysics, and experimental techniques converge. Axions in this mass range are theoretically well motivated, can arise in ultraviolet-complete models, and can have significant cosmological impacts as dark matter or dark radiation. In parallel, their efficient production in stellar and supernova environments provides powerful astrophysical probes. Here, we provide a comprehensive overview of meV axions across these domains, highlighting both established results and open questions. We discuss the theoretical underpinnings of meV axions, their cosmological and astrophysical signatures, and the diverse experimental strategies -- ranging from helioscopes and haloscopes to quasiparticle systems and large-volume Cherenkov detectors -- that aim to explore this regime. The convergence of these approaches emphasizes the pivotal role of the meV mass range for axion discovery in the coming years, identifying meV axions as a key probe for testing beyond-Standard-Model physics. This review document is the direct outcome of the discussions at the dedicated workshop "The meV Mass Axion Frontier: Challenges and Opportunities", held at Laboratori Nazionali di Frascati (IT) on 27--28 October 2025, and organized by the EU funded COST Action "Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments" (CA21106, https://www.cost.eu/actions/CA21106). Its aim is to provide an overview of current efforts in meV axion research, their motivations, and the research goals that animate the community involved in this search.

hep-ph↗

arXiv2026

The COSMIC WISPers White Paper: The physics case for Weakly Interacting Slim Particles

Axions and other very weakly interacting slim particles (WISPs), with masses below 1 GeV, arise naturally in many extensions of the Standard Model of particle physics. In particular, they could offer a new framework to explain the nature of dark matter and may help address a range of puzzling observations in astrophysics and particle physics. This review provides an overview of ongoing WISP searches and outlines the prospects for the next decade, spanning their theoretical motivation, indirect signatures in astrophysical observations, and dedicated laboratory experiments. It is based on the work carried on by the EU-funded COST Action ``Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments'' (CA21106, https://www.cost.eu/actions/CA21106). This network plays a key role in coordinating and supporting WISP searches across Europe, while also contributing to the development of a roadmap aimed at securing European leadership in this research area. It is emphasized that Europe is currently pursuing a rich, diverse, and cost-effective experimental program, with the potential to deliver one or more transformative discoveries.

hep-ph↗

arXiv2025

Probing the Axion-Nucleon Coupling with Supergiant Stars

A finite axion-nucleon coupling enables the production of axions in stellar environments via the thermal excitation and subsequent de-excitation of the $^{57}$Fe isotope. Given its low-lying excited state at 14.4 keV, $^{57}$Fe can be efficiently excited in the hot cores of supergiant stars, possibly leading to axions emission. The conversion of these axions into photons in the Galactic magnetic field results in a characteristic 14.4 keV line, potentially detectable by hard X-ray telescopes such as NASA's Nuclear Spectroscopic Telescope Array (NuSTAR). In this work, we present the first constraints on axion-nucleon couplings derived from \textsc{NuSTAR} observations of Betelgeuse and discuss the potential insights that could be gained from detecting this line in other nearby supergiants. Our results establish significantly more stringent bounds than those obtained from solar observations, setting a limit of $|g_{a\gamma} g_{aN}^{\mathrm{eff}}| < (1.2 - 2.7) \times 10^{-20}$ GeV$^{-1}$ for $m_a \lesssim 10^{-10}$ eV.

hep-ph↗

arXiv2023

The Sun as a target for axion dark matter detection

The exploration of the parameter space of axion and axion-like particle dark matter is a major aim of the future program of astroparticle physics investigations. In this context, we present a possible strategy that focuses on detecting radio emissions arising from the conversion of dark matter axions in the Sun's magnetic field, including conversion in sunspots. We demonstrate that near-future low-frequency radio telescopes, such as the SKA Low, may access regions of unexplored parameter space for masses $m_a\lesssim 10^{-6}$ eV.

hep-ph↗

arXiv2023

Searching for WIMPs with TREX-DM: achievements and challenges

The TREX-DM detector, a low background chamber with microbulk Micromegas readout, was commissioned in the underground laboratory of Canfranc (LSC) in 2018. Since then, data taking campaigns have been carried out with Argon and Neon mixtures, at different pressures from 1 to 4 bar. By achieving a low energy threshold of 1 keV$_{ee}$ and a background level of 80 counts keV$^{-1}$ Kg$^{-1}$ day$^{-1}$ in the region from 1 to 7 keV$_{ee}$, the experiment demonstrates its potential to search for low-mass WIMPs. Two of the most important challenges currently faced are the reduction of both, background level and energy threshold. With respect to the energy threshold, recently a new readout plane is being developed, based on the combination of Micromegas and GEM technologies, aiming to have a pre-amplification stage that would permit very low energy thresholds, close to the single-electron ionization energy. With respect to the background reduction, apart from studies to identify and minimize contamination population, a high sensitivity alpha detector is being developed in order to allow a proper material selection for the TREX-DM detector components. Both challenges, together with the optimization of the gas mixture used as target for the WIMP detection, will take TREX-DM to explore regions of WIMP's mass below 1 GeV c$^{-2}$.

physics.ins-det↗

arXiv2022

Probing the axion-nucleon coupling with the next generation of axion 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 Fe-57 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.

hep-ph↗

arXiv2016

IAXO, next-generation of helioscopes

The International Axion Observatory (IAXO) is a forth generation axion helioscope designed to detect solar axions and axion-like particles (ALPs) with a coupling to the photon $g_{aγ}$ down to a few $10^{-12}$ GeV$^{-1}$, 1.5 orders of magnitude beyond the current best astrophysical and experimental upper bounds. This range includes parameter values invoked in the context of the observed anomalies in light propagation over astronomical distances and to explain the excessive cooling observed in a number of stellar objects. Here we review the status of the IAXO project and of its potential to probe the most physically motivated regions of the axion/ALPs parameter space.

physics.ins-det↗