Search for dark matter axions with the Orpheus experiment

Axions are well motivated particles that could make up most or all of the dark matter if they have masses below $100\mu \mathrm{eV}$. Microwave cavity techniques comprised of closed resonant structures immersed in solenoid magnets are sensitive to dark matter axions with masses of a few $\mu \mathrm{eV}$ but face difficulties scaling to higher masses. We present the a novel detector architecture consisting of an open, Fabry–Pérot resonator and a series of current-carrying wire planes and demonstrate this technique with a search for dark matter axionlike particles called Orpheus. This search excludes dark matter axionlike particles with masses between 68.2 and $76.5\mu \mathrm{eV}$ and axion-photon couplings greater than $4\times 10^{-7}{\mathrm{GeV}}^{-1}$. We project that the fundamental sensitivity of this technique could be extended to be sensitive to couplings below $1\times 10^{-15}{\mathrm{GeV}}^{-1}$, consistent with the DFSZ model of QCD axions.

Figure 1

Model of the Orpheus experiment. The experiment consists of a regular grid of wires braced by a pair of reflectors forming a Fabry–Pérot resonator. The wire planes and reflectors are supported on rails permitting the frequency of the resonator to be adjusted with optimal alignment of the magnetic field supplied by the wires.

Figure 2

Simulated magnetic and electric fields on axis within the Fabry–Pérot resonator. Both fields are primarily in the vertical direction relative to Fig. 1, perpendicular to the wires in the wire planes. The maximum magnetic field for this experiment was 8.5 gauss, and the electric field of the ${\mathrm{TEM}}_{00-19}$ mode is shown on same scale in arbitrary units for clarity.

Figure 3

$V_{nlm}$ as defined in Eq. (3) for two different wire frame spacings. 9.1 mm spacing (solid), 8.1 mm spacing (dashed).

Figure 4

Axion-photon coupling $g_{a\gamma \gamma }$ and masses excluded from this experiment, assuming axionlike particles make up all of the local dark matter density. Limits from the laser-based experiments GammeV [19] and ALPS [20] and the solar experiment CAST [21] are shown for comparison.

Figure 5

Expected sensitivity to axion-photon coupling of the proposed experiment technique for the experimental parameters listed in Table 1 assuming axions make up all of the local dark matter density. Also shown for comparison are limits set by existing microwave cavity experiments [9, 11, 22, 23, 24] and solar axion experiments [21]. The ADMX experiment is currently being upgraded to expand its sensitivity to $40\mu \mathrm{eV}$ at DFSZ sensitivity, making the proposed technique a natural extension of the search range. [25].