Broadband Solenoidal Haloscope for Terahertz Axion Detection

We introduce the Broadband Reflector Experiment for Axion Detection (BREAD) conceptual design and science program. This haloscope plans to search for bosonic dark matter across the $[{10}^{-3},1]\mathrm{eV}$ ([0.24, 240] THz) mass range. BREAD proposes a cylindrical metal barrel to convert dark matter into photons, which a novel parabolic reflector design focuses onto a photosensor. This unique geometry enables enclosure in standard cryostats and high-field solenoids, overcoming limitations of current dish antennas. A pilot $0.7{\mathrm{m}}^2$ barrel experiment planned at Fermilab is projected to surpass existing dark photon coupling constraints by over a decade with one-day runtime. Axion sensitivity requires $<{10}^{-20}\mathrm{W}/\sqrt{\mathrm{Hz}}$ sensor noise equivalent power with a 10 T solenoid and $10{\mathrm{m}}^2$ barrel. We project BREAD sensitivity for various sensor technologies and discuss future prospects.

Figure 1

(a) BREAD reflector geometry: rays (yellow lines) emitted from the cylindrical barrel, which is parallel to an external magnetic field ${\mathbf{B}}_{\mathrm{ext}}$ from a surrounding solenoid (not shown) and focused at the vertex by a parabolic surface of revolution. (b) Radial intensity distribution $rI(r)$ expected from DM velocity effects in the $xy$ plane at the focal spot using ray tracing, for the BREAD geometry as in (a) with $R=20\mathrm{cm}$ (blue) and for a conventional plane-parabolic mirror setup used in other experiments [69, 70, 71, 72, 73] with the same emitting surface area (gray). (c) Full field simulation at around 15 GHz including a preliminary coaxial horn design. (d) Electric (blue) and magnetic (orange) field distribution and time-averaged Poynting flux along the $z$ direction in the $xy$ plane at the focal spot. (e) Schematic setup in cryostat for pilot dark photon searches.

Figure 2

Projected BREAD sensitivity by sensor technology (bold labels, see Table 1) for dark photons $A^{\prime }$ (left) and axions $a$ (right). This assumes signal-to-noise ratio $\mathrm{SNR}=5$ (significance $Z=5$ for photocounters), signal efficiency ${\epsilon }_{\mathrm{sig}}=0.5$, and dish area $A_{\mathrm{dish}}=10{\mathrm{m}}^2$. Blue shading shows existing constraints from Ref. [96]. Benchmark axion predictions include QCD axion models [146] (green band), cogenesis [67] (green dots), KSVZ [82, 83] and DFSZ [80, 81] (green lines). Sensitivity scaling assumes background-limited operation where signal-power limits scale as $\sqrt{\mathrm{\Delta }t}$ for runtime $\mathrm{\Delta }t$ and linearly with improved NEP.