New Constraints on Dark Photon Dark Matter with a Millimeter-Wave Dielectric Haloscope

Abstract

Dark matter remains one of the most profound and unresolved mysteries in modern physics. To unravel its nature, numerous haloscope experiments have been implemented across various mass ranges. However, very few haloscope experiments conducted within millimeter-wave frequency range, which is in the favored mass region for well-motivated dark matter candidates. Here we designed and constructed a millimeter-wave dielectric haloscope featuring a dark matter detector composed of dielectric disks and a mirror. Using this setup, we conducted a search for randomly polarized dark photon dark matter and found no evidence for its existence. Our results established new constraints on the kinetic mixing parameter in the mass range from $387.72$ to $391.03$ $μeV$, improving the existing limits by two orders of magnitude. With future enhancements, our system has the potential to explore new parameter space for dark photon as well as axion dark matter within the millimeter-wave frequency range.

Figures (17)

• Figure 1: Experimental Setup. (a) Simplified diagram of the experiment apparatus for the dark photon search. $A'$ and $\gamma$ stand for the dark photon field and the converted photons, respectively. The emitted photons are collected by an antenna with an aperture of $39.2\,\rm{mm}$. The receiver chain can detect the signal with high efficiency. (b) Diagram of the dielectric stack. The stack is comprised of one gold-coating aluminum mirror and four $\rm{LaAlO_3}$ disks with refractive index $n \approx 5$. The disks and mirror are separated by aluminum holders. The inner diameter of the holder is $D\approx32.0\,\rm{mm}$, while $d_v\approx1.580\, \rm{mm}$ and $d_e\approx0.320\, \rm{mm}$ denote the spacing and thickness of the disks, respectively.
• Figure 2: Results of boost factor calibration with the reflectivity test method. (a) The reflectivity of the first dielectric disk (the bottom one in the stack). The blue solid line is the measurement data, and the red dashed line is the fitting result with $\mathcal{R}$. The inset shows the scheme of the reflectivity test using a vector network analyzer (VNA). (b) The reflectivity of stack. The blue solid line and red dashed line stand for experiment data and the fitting result with the one-dimension multiple layers model, respectively. (c) Boost factor as a function of frequency. The light blue shaded region indicates the range of boost factor obtained by varying the stack and antenna parameters within their uncertainties. The magenta line shows the minimum value of boost factor.
• Figure 3: Data analysis of the frequency range from $94.014 \,\rm{GHz}$ to $94.202 \,\rm{GHz}$. (a) The normalized power excess after convolution. (b) The normalized power excess distribution. The blue bars show the histogram of normalized power excess, and the red solid line is the fitting result with normal Gaussian distribution.
• Figure 4: Constraints on the dark photon with kinetic mixing $\chi$ and dark photon mass. (a) The blue shaded region shows the $90\%$ confidence limits set by this work. The light gray region refers to the result of XENON1T aprile_emission_2022, and the deep gray region is the astrophysical bound set by Arias et al arias_wispy_2012. (b) This work along with other experimental searches in an extended dark photon mass range. Constraints on kinetic mixing from MADMAX madmax_collaboration_first_2025, DOSUE kotaka_search_2023, QC fan_one-electron_2022 and Tokyo knirck_first_2018 are shown in gray.
• Figure 5: Schematic diagram of the experiment apparatus for dark photon search.